Physical
Activity
and
Health

A Report of the Surgeon General

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES
Centers for Disease Control and Prevention
National Center for Chronic Disease Prevention and Health Promotion
The President's Council on Physical Fitness and Sports


Suggested Citation

U.S. Department of Health and Human Services. Physical Activity and Health:
A Report of the Surgeon General. Atlanta, GA: U.S. Department of Health and
Human Services, Centers for Disease Control and Prevention, National
Center for Chronic Disease Prevention and Health Promotion, 1996.

For sale by the Superintendent of Documents,
P.O. Box 371954, Pittsburgh, PA 15250-7954,
      s/No17-023-00196-5


Message from Donna E. Shalala
Secretary of HeaIth and Human Services

The United States has led the world in understanding and promoting the
benefits of physical activity. In the 1950s we launched the first national effort to
encourage young Americans to be physically active, with a strong emphasis on
participation in team sports. In the 1970s we embarked on a national effort to
educate Americans about the cardiovascular benefits of vigorous activity, such as
running and playing basketball. And in the 1980s and 1990s we made break-
through findings about the health benefits of moderate-intensity activities, such as
walking, gardening, and dancing.

Now, with the publication of this first Surgeon General's report on physical
activity and health, which I commissioned in 1994, we are poised to take another
bold step forward. This landmark review of the research on physical activity and
health-the most comprehensive ever-has the potential to catalyze a new physical
activity and fitness movement in the United States. It is a work of real significance,
on par with the Surgeon General's historic first report on smoking and health
published in 1964.

This report is a passport to good health for all Americans. Its key finding is that
people of all ages can improve the quality of their lives through a lifelong practice
of moderate physical activity. You don't have to be training for the Boston Marathon
to derive real health benefits from physical activity. A regular, preferably daily
regimen of at least 30-45 minutes of brisk walking, bicycling, or even working
around the house or yard will reduce your risks of developing coronary heart
disease, hypertension, colon cancer, and diabetes. And if you're already doing that,
you should consider picking up the pace: this report says that people who are
already physically active will benefit even more by increasing the intensity or
duration of their activity.

This watershed report comes not a moment too soon. We have found that 60
percent-well over half-of Americans are not regularly active. Worse yet, 25
percent of Americans are not active at all. For young people-the future of our
country-physical activity declines dramatically during adolescence. These are
dangerous trends. We need to turn them around quickly, for the health of our
citizens and our country.

We will do so only with a massive national commitment-beginning now, on
the eve of the Centennial Olympic Games, with a true fitness Dream Team drawing
on the many forms of leadership that make up our great democratic society.
Families need to weave physical activity into the fabric of their daily lives. Health
professionals, in addition to being role models for healthy behaviors, need to
encourage their patients to get out of their chairs and start fitness programs tailored
to their individual needs. Businesses need to learn from what has worked in the past


and promote worksite fitness, an easy option for workers. Community leaders need
to reexamine whether enough resources have been devoted to the maintenance of
parks, playgrounds, community centers, and physical education. Schools and
universities need to reintroduce daily, quality physical activity as a key component
of a comprehensive education. And the media and entertainment industries need to
use their vast creative abilities to show all Americans that physical activity is
healthful and fun-in other words, that-it is attractive, maybe even glamorous!
We Americans always find the will to change when change is needed. I believe
we can team up to create a new physical activity movement in this country. In doing
so, we will save precious resources, precious futures, and precious lives. The time
for action-and activity-is now.


Foreword

This first Surgeon General's report on physical activity is being released on the
eve of the Centennial Olympic Games- the premiere event showcasing the worlds
greatest athletes. It is fitting that the games are being held in Atlanta, Georgia, home
of the Centers for Disease Control and Prevention (CDC), the lead federal agency
in preparing this report. The games' loo-year celebration also coincides with the
CDC's landmark 50th year and with the 40th anniversary of the President's Council
on Physical Fitness and Sports (PCPFS), the CDC's partner in developing this
report. Because physical activity is a widely achievable means to a healthier life, this
report directly supports the CDC's mission- to promote health and quality of life
by preventing and controlling disease, injury, and disability. Also clear is the link
to the PCPFS; origin-ally established as part of a national campaign to help shape up
America's younger generation, the Council continues today to promote physical
activity, fitness, and sports for Americans of all ages.
The Olympic Games represent the summit of athletic achievement. The
Paralympics, an international competition that will occur later this summer in
Atlanta, represents the peak of athletic accomplishment for athletes with disabili-
ties. Few of us will approach these levels of performance in our own physical
endeavors. The good news in this report is that we do not have to scale Olympian
heights to achieve significant health benefits. We can improve the quality of our lives
through a lifelong practice of moderate amounts of regular physical activity of
moderate or vigorous intensity. An active lifestyle is available to all.
Many Americans may be surprised at the extent and strength of the evidence
linking physical activity to numerous health improvements. Most significantly,
regular physical activity greatly reduces the risk of dying from coronary heart
disease, the leading cause of death in the United States. Physical activity also reduces
the risk of developing diabetes, hypertension, and colon cancer; enhances mental
health; fosters healthy muscles, bones and joints; and helps maintain function and
preserve independence in older adults.

The evidence about what helps people incorporate physical activity into their
lives is less clear-cut. We do know that effective strategies and policies have taken
place in settings as diverse as physical education classes in schools, health promo-
tion programs at worksites, and one-on-one counseling by health care providers.
However, more needs to be learned about what helps individuals change their
physical activity habits and how changes in community environments, policies, and
social norms might support that process.

Support is greatly needed if physical activity is to be increased in a society as
technologically advanced as ours. Most Americans today are spared the burden of
excessive physical labor. Indeed, few occupations today require significant physical


acttvtty, and most people use motorized transportation to get to work and to perform
routine errands and tasks. Even leisure time is increasingly filled with sedentary
behaviors, such as watching television, "surfing" the Internet, and playing video
games.

Increasing physical activity is a formidable public health challenge that we must
hasten to meet. The stakes are high, and the potential rewards are momentous:
preventing premature death, unnecessary illness, and disability; controlling health
care costs\ and maintaining a high quality of life into old age.

David Satcher, M.D., Ph.D.                 Philip R. Lee, M.D.

Director
Centers for Disease Control
and Prevention

Assistant Secretary
for Health

Florence Griffith Joyner
Tom McMillen
Co-Chairs
President's Council on
Physical Fitness and Sports


    Preface
from the Surgeon General
U.S. Public Health Service

I am pleased to present the first report of the Surgeon General on physical
activity and health. For more than a century, the Surgeon General of the Public
Health Service has focused the nation's attention on important public health issues.
Reports from Surgeons General on the adverse health consequences of smoking
triggered nationwide efforts to prevent tobacco use. Reports on nutrition, violence,
and HIV/AIDS-to name but a few-have heightened America's awareness of
important public health issues and have spawned major public health initiatives.
This new report, which is a comprehensive review of the available scientific
evidence about the relationship between physical activity and health status, follows
in this notable tradition.

Scientists and doctors have known for years that substantial benefits can be
gained from regular physical activity. The expanding and strengthening evidence
on the relationship between physical activity and health necessitates the focus this
report brings to this important public health challenge. Although the science of
physical activity is a complex and still-developing field, we have today strong
evidence to indicate that regular physical activity will provide clear and substantial
health gains. In this sense, the report is more than a summary of the science-it is
a national call to action.

We must get serious about improving the health of the nation by affirming our
commitment to healthy physical activity on all levels: personal, family, community,
organizational, and national. Because physical activity is so directly related to
preventing disease and premature death and to maintaining a high quality of life,
we must accord it the same level of attention that we give other important public
health practices that affect the entire nation. Physical activity thus joins the front
ranks of essential health objectives, such as sound nutrition, the use of seat belts,
and the prevention of adverse health effects of tobacco.

The time for this emphasis is both opportune and pressing. As this report
makes clear, current levels of physical activity among Americans remain low, and
we are losing ground in some areas. The good news in the report is that people can
benefit from even moderate levels of physical activity. The public health implica-
tions of this good newsare vast: the tremendous health gains that could be realized
with even partial success at improving physical activity among the American
people compel us to make a commitment and take action. With innovation,
dedication, partnering, and a long-term plan, we should be able to improve the
health and well-being of our people.


This report is not the final word. More work will need to be done so that we can
determine the most effective ways to motivate all Americans to participate in a level
of physical activity that can benefit their health and well-being. The challenge that
lies ahead is formidable but worthwhile. 1 strongly encourage all Americans to join
us in this effort.

Audrey F. Manley, M.D`., M.P.H.
Surgeon General (Acting)


Physical Activity and Health

Acknowledgments

Editors

Steven N. Blair, P.E.D., Senior Scientific Editor,
Director of Research and Director, Epidemiology
and Clinical Applications, The Cooper Institute for
Aerobics Research, Dallas, Texas.

Adele L. Franks, M.D., Scientific Editor, Assistant
Director for Science, National Center for Chronic
Disease Prevention and Health Promotion, Centers
for Disease Control and Prevention, Atlanta, Georgia.

Dana M. Shelton, M.P.H., Managing Editor,
Epidemiologist, Office on Smoking and Health,
National Center for Chronic Disease Prevention and
Health Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

John R. Livengood, M.D., M.Phil., Coordinating
Editor, Deputy Director, Epidemiology and
Surveillance Division, National Immunization
Program, (formerly, Associate Director for Science,
Division of Chronic Disease Control and Community
Intervention, National Center for Chronic Disease
Prevention and Health Promotion), Centers for
Disease Control and Prevention, Atlanta, Georgia.

Frederick L. Hull, Ph.D., Technical Editor, Technical
Information and Editorial Services Branch, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Byron Breedlove, M.A., Technical Editor, Technical
Information and Editorial Services Branch, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

This report was prepared by the Department of
Health and Human Services under the direction of
the Centers for Disease Control and Prevention,
National Center for Chronic Disease Prevention and
Health Promotion, in collaboration with the
President's Council on Physical Fitness and Sports.

David Satcher, M.D., Ph.D., Director, Centers for
Disease Control and Prevention, Atlanta, Georgia.

J~~I~CS S. Marks, M.D., M.P.H., Director, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prcvcntion, Atlanta, Georgia.

Virginia S. Bales, M.P.H., Deputy Director, National
Ccntcr for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
f'rcvcntion, Atlanta, Georgia.

f.isa A. Daily, Assistant Director for Planning,
f:valuation, and Legislation, National Center for
(:hronic Disease Prevention and Health Promotion,
(:cntcrs for Disease Control and Prevention,
)\tlanta, Georgia.

Marjorie A. Speers, Ph.D., Behavioral and Social
\cicnccs Coordinator, Office of the Director,
(lormcrly, Director, Division of Chronic Disease
(:oritrol and Community Intervention, National
(:ctircr for Chronic Disease Prevention and Health
Promotion), Centers for Disease Control and
f'rcvention, Atlanta, Georgia.

f:rcclerick L. Trowbridge, M.D., Director, Division of
Nutrition and Physical Activity, National Center for
Chronic Disease Prevention and Health Promotion,
Ccmcrs for Disease Control and Prevention, Atlanta,
Georgia.

l'lorcnce Griffith Joyner, Co-Chair, President's
C:ouncil on Physical Fitness and Sports, Washington,
D.C.

C. Thomas McMillen, Co-Chair, President's Council
on Physical Fitness and Sports, Washington, D.C.
5lmh-a P. Perlmutter, Executive Director, President's
Council on Physical Fitness and Sports, Washington,
D.C.

Editorial Board

Carl J. Caspersen, Ph.D., Epidemiologist, Division
of Nutrition and Physical Activity, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Aaron R. Folsom, M.D., M.P.H., Professor, Division
of Epidemiology, School of Public Health, University
of Minnesota, Minneapolis, Minnesota.

vii


A Report of the Surgeon General

William L. Haskell, Ph.D., Professor of Medicine,
Stanford University, Palo Alto, California.

Arthur S. Leon, M.D., M.S., Henry L. Taylor Professor
and Director of the Laboratory of Physiological
Hygiene and Exercise Science, Division of Kinesiology,
University of Minnesota, Minneapolis, Minnesota.

James F. Sallis, Jr., Ph.D., Professor, Department of
Psychology, San Diego State University, San Diego,
California.

Martha L. Slattery, Ph.D., M.P.H., Professor,
Department of Oncological Sciences, University of
Utah Medical School, Salt Lake City, Utah.

Christine G. Spain, `M.A., Director, Research,
Planning, and Special Projects, President's Council
on Physical Fitness and Sports, Washington, D.C.

Jack H. Wilmore, Ph.D., Professor, Department of
Kinesiology and Health Education, University of
Texas at Austin, Austin, Texas.

Planning Board

Terry L. Bazzarre, Ph.D., Science Consultant,
American Heart Association, Dallas, Texas.

Steven N. Blair, P.E.D., Senior Scientific Editor,
Director of Research and Director, Epidemiology and
Clinical Applications, The Cooper Institute for
Aerobics Research, Dallas, Texas.

Willis R. Foster, M.D., Office of Disease Prevention
and Technology Transfer, National Institute of
Diabetes and Digestive and Kidney Diseases, National
Institutes of Health, Bethesda, Maryland.

Patty Freedson, Ph.D., Department of Exercise
Science, University of Massachusetts, Amherst,
Massachusetts. Represented the American Alliance
for Health, Physical Education, Recreation and Dance.

William R. Harlan, M.D., Associate `Director for
Disease Prevention, Office of the Director, National
Institutes of Health, Bethesda, Maryland.

James A. Harrell, M.A., Deputy Commissioner,
Administration on Children, Youth, and Families,
(formerly, Deputy Director, Office of Disease
Prevention and Health Promotion, Office of the
Assistant Secretary for Health, Department of Health
and Human Services), Washington, D.C.

Richard W. Lymn, Ph.D., Muscle Biology Branch,
National Institute of Arthritis and Musculoskeletal
and Skin Diseases, National Institutes of Health,
Bethesda, Maryland.

Russell R. Pate, Ph.D., Chairman, Department of
Exercise Science, University of South Carolina,
Columbia, South Carolina. Represented the American
College of Sports Medicine.

Sandra P. Perlmutter, Executive Director, President's
Council on Physical FitnessandSports, Washington,
D.C.

Bruce G. Simons-Morton, Ed.D., M.P.H., Behavioral
Scientist, Prevention Research Branch, National
Institute of Child Health and Human Development,
National Institutes of Health, Bethesda, Maryland.

Denise G. Simons-Morton, M.D., Ph.D., Leader,
Prevention Scientific Research Group, DECA,
National Heart, Lung, and Blood Institute, National
Institutes of Health, Bethesda, Maryland.

Contributing Authors

Lynda A. Anderson, Ph.D., Public Health Educator,
Division of Adult and Community Health, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Carol C. Ballew, Ph.D., Epidemiologist, Division of
Nutrition and Physical Activity, National Center for
Chronic Disease Prevention and Health Promotion,
Centers for Disease Control and Prevention, Atlanta,
Georgia.

Jack W. Berryman, Ph.D., Professor, Department of
Medical History and Ethics, School of Medicine,
University of Washington, Seattle, Washington.

Lawrence R. Brawley, Ph.D., Professor, University of
Waterloo, Ontario, Canada.

David R. Brown, Ph.D., Health Scientist, Division of
Nutrition and Physical Activity, National Center for
Chronic Disease Prevention and Health Promotion,
Centers for Disease Control and Prevention, Atlanta,
Georgia.

.
VIII


Physical Activity and Health

Lee S. CupIan, M.D., Ph.D., Medical Epidemiologist,
Epidcruiology and Statistics Branch, Division of
C&lnccr prevention and Control, National Center for
Cllronic Disease Prevention and Health Promotion,
Ccntcrs for Disease Control and Prevention, Atlanta,
Georgia.

R,+h J. Coatcs, Ph.D., Chief, Epidemiology Section,
Division of Cancer Prevention and Control, National
ccntcr for Chronic Disease Prevention and Health
f'romotion, Centers for Disease Control and
frcvcntion, Atlanta, Georgia.

C,lrlos J. Crespo, Dr.P.H., M.S., F.A.C.S.M., Public
flculth Analyst, National Heart, Lung, and Blood
Itlstitutc, National Institutes of Health, Bethesda,
Xlaryland.

I.orctta DiPietro, Ph.D., M.P.H., Assistant Fellow
and Assistant Professor of Epidemiology and
I'ublic Health, The John B. Pierce Laboratory and
Y;IIC University School of Medicine, New Haven,
(;onnccticut.

124 K. Dishman, Ph.D., Professor, Department of
f:scrcisc Science, University of Geoigia, Athens,
Georgia.

Michael M. Engelgau, M.D., Chief, Epidemiology
:~nd Statistics Branch, Division of Diabetes
Translation, National Center for Chronic Disease
I'rcvcntionand Health Promotion, Centers for Disease
(:ontrol and Prevention, Atlanta, Georgia.

\Valtcr H. Ettinger, M.D., Professor, Internal Medicine
and Public Health Sciences, Bowman Gray School of
Medicine, Winston-Salem, North Carolina.

David S. Freedman, Ph.D., Epidemiologist, Division
of Nutrition and Physical Activity, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Frederick Fridinger, Dr.P.H., C.H.E.S.., Public Health
Educator, Division of Nutrition and Physical
Activity, National Center for Chronic Disease
Prevention and Health Promotion, Centers for
Disease Control and Prevention, Atlanta, Georgia.

Gregory W. Heath, D.Sc., M.P.H., Epidemiologist/
Exercise Physiologist, Division of Adult and
Community Health, National Center for Chronic
Disease Prevention and Health Promotion, Centers
for Disease Control and Prevention, Atlanta, Georgia.

Wendy A. Holmes, M.S., Health Communications
Specialist, Division of Nutrition and Physical
Activity, National Center for Chronic Disease
Prevention and Health Promotion, Centers for
~Disease Control and Prevention, Atlanta, Georgia.

Elizabeth H. Howze, Sc.D., Associate Director for
Health Promotion, Division* of Nutrition and
Physical Activity, National Center for Chronic
Disease Prevention and Health Promotion, Centers
for Disease Control and Prevention, Atlanta,
Georgia.

Laura K. Kann, Ph.D., Chief, Surveillance Research
Section, Division of Adolescent and School Health,
National Center for Chronic Disease Prevention and
Health Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Abby C. King, Ph.D., Assistant Professor of Health
Research and Policy and Medicine, Stanford
University School of Medicine, Palo Alto, California.

Harold W. Kohl, III, Ph.D., Director of Research,
Baylor College of Medicine, Baylor Sports Medicine
Institute, Houston, Texas.

Jeffrey P. Koplan, M.D., M.P.H., President, Prudential
Center for Health Care Research, Atlanta, Georgia.

Andrea M. Kriska, Ph.D., M.S., Assistant Professor,
Department of Epidemiology, Graduate School of
Public Health, University of Pittsburgh, Pittsburgh,
Pennsylvania.

Barbara D. Latham, R.D., M.P.H., Public Health
Nutritionist, Division of Nutrition and Physical
Activity, National Center for Chronic Disease
Prevention and Health Promotion, Centers for
Disease Control and Prevention, Atlanta, Georgia.

I-Min Lee, M.B.B.S., Sc.D., Assistant Professor
of Medicine, Harvard Medical School, Boston,
Massachusetts.

ix


A Report of the Surgeon General

Elizabeth Lloyd, M.S., Statistician, Division of
Nutrition and Physical Activity, National Center for
Chronic Disease Prevention and Health Promotion,
Centers for Disease Control and Prevention, Atlanta,
Georgia.

Bess H. Marcus, Ph.D., Associate Professor of
Psychiatry and Human Behavior, Division of Behavior
and Preventive Medicine, Miriam Hospital and Brown
University School of Medicine, Providence, Rhode
Island.

DyannMatson-Koffman,Dr.P.H.,M.P.H., C.H.E.S.,
Public Health Educator, Division of Adult and
Community Health, National Center for Chronic
Disease Prevention and Health Promotion, Centers
for Disease ControI and Prevention, Atlanta,
Georgia.

Marion R. Nadel, Ph.D., Epidemiologist, Epidemiology
and Statistics Branch, Division of Cancer Prevention
and Control, National Center for Chronic Disease
Preventionand Health Promotion, Centers for Disease
Control and Prevention, Atlanta, Georgia.

Eva Obarzanek, Ph.D., M.P.H., R.D., Nutritionist,
National Heart, Lung, and Blood Institute, National
Institutes of Health, Bethesda, Maryland.

Christine M. Plepys, M.S., Health Statistician, Division
of Health Promotion Statistics, National Center for
Health Statistics, Centers for Disease Control and
Prevention, Hyattsville, Maryland.

Michael L. Pollock, Ph.D., Professor of Medicine,
Physiology and Health and Human Performance;
Director, Center for Exercise Science, University of
Florida, Gainesville, Florida.

Michael Pratt, M.D., M.P.H., Medical Epidemiologist,
Division of Nutrition and Physical Activity, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Paul T. Raford;M.D., M.P.H.,Special Assistant to the
Regional Health Administrator, Environmental
Justice Programs, Office of Public Health Science,
Region VIII, Department of Health and Human
Services, U.S. Public Health Service, Denver,
Colorado.

W. Jack Rejeski, Ph.D., Professor, Health and Sports
Science, Wake Forest University, Winston-Salem,
North Carolina.

Richard B. Rothenberg, M.D., M.P.H., F.A.C.P.,
Professor and Director, Preventive Medicine
Residency Program, Department of Family and
Preventive Medicine, Emory University School of
Medicine, Atlanta, Georgia.

Mary K. Serdula, M.D., M.P.H., Acting Branch Chief,
Chronic Disease Prevention Branch, Division of
Nutrition and Physical Activity, National Center for
Chronic Disease Prevention and Health Promotion,
Centers for Disease Control and Prevention, Atlanta,
Georgia.

Charlotte A. Schoenborn, M.P.H., Health Statistician,
National Center for Health Statistics, Centers for
Disease Control and Prevention, Hyattsville,
Maryland.

Denise G. Simons-Morton, M.D., Ph.D., Leader,
Prevention Scientific Research Group, DECA,
National Heart, Lung, and Blood Institute, National
Institutes of Health, Bethesda, Maryland.

Elaine J. Stone, Ph.D., M.P.H., Health Scientist
Administrator, Division of Epidemiology and Clinical
Applications, National Heart, Lung, and Blood
Institute, National Institutes of Health, Bethesda,
Maryland.

Marlene K. Tappe, Ph.D., Visiting Behavioral
Scientist, Division of Adolescent and School Health,
National Center for Chronic Disease Prevention and
Health Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Wendell C. Taylor, Ph.D., M.P.H., Assistant Professor
of Behavioral Sciences, School of Public Health,
University of Texas Health Science Center at Houston,
Houston, Texas.

CharlesW. Warren, Ph.D., Statistician/Demographer,
Division of Adolescent and School Health, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Deborah R. Young, Ph.D., Assistant Professor of
Medicine, Division of Internal Medicine, The Johns
Hopkins School of Medicine, Baltimore, Maryland.

X


Physical Activity and Health

Senior Reviewers

Elizabeth A. Arendt, M.D., Associate Professor of
Orthopaedics, University of Minnesota, Minneapolis,
>jtnnesota. Member, President's Councilon Physical
Fitness and Sports.

Elsworth R. Buskirk, Ph.D., Professor of Applied
Physiology, Emeritus, Pennsylvania State University,
University Park, Pennsylvania.

B. Don Franks, Ph.D., Professor and Chair,
Department of Kinesiology, Louisiana State
University, Baton Rouge, Louisiana. Senior Program
Advisor, President's Council on Physical Fitness
and Sports.

\Villiam R. Harlan, M.D., Associate Director for
Disease Prevention, Office of the Director, National
Institutes of Health, Bethesda, Maryland.

William P. Morgan, Ed.D., Professor, Department of
Kincsiology, University of Wisconsin-Madison,
Madison, Wisconsin.

Ralph S. Paffenbarger,Jr., M.D., Dr.P.H., Professor of
Epidemiology (Retired-Active), Stanford University
School of Medicine, Stanford, California.

Russell R. Pate, Ph.D., Chairman, Department of
Escrcise Science, University of South Carolina,
cIolumbia,SouthCarolina. Represented the American
(:ollcge of Sports Medicine.

Roy J. Shephard, M.D., Ph.D., D.P.E., F.A.C.S.M.,
Professor EmeritusofApplied Physiology, University
of Toronto, Toronto, Canada.

Peer Reviewers

Barbara E. Ainsworth, Ph.D., M.P.H., Associate
Professor, Department of Epidemiology and
Biosratistics, Department ofExercise Science, School
of Public Health, University of South Carolina,
Columbia, South Carolina.

Tom Baranowski, Ph.D., Professor, Department of
Behavioral Science, University of Texas, M. D.
.-\nderson Cancer Center, Houston, Texas.

Oded Bar-Or, M.D., Professor of Pediatrics and
Director, Children's Exercise and Nutrition Centre,
McMaster University, Chedoke Hospital Division,
Hamilton, Ontario, Canada.

Charles B. Corbin, Ph.D., Professor, Department of
Exercise Science and Physical Education, Arizona
State University, Tempe, Arizona.

Kirk J. Cureton, Ph.D., Professor and Head,
Department of Exercise Science, University of
Georgia, Athens, Georgia.

Gail P. Dalsky, Ph.D., Assistant Professor ofMedicine
(in residence), University of Connecticut Health
Center, Farmington, Connecticut.

Nicholas A. DiNubile, M.D., Clinical Assistant
Professor, Department of Orthopaedic Surgery,
Hospital of the University of Pennsylvania; Chief,
Orthopaedic Surgery and Sports Medicine, Delaware
County Memorial Hospital, Drexel Hill, Pennsylvania.

BarbaraL. Drinkwater, Ph.D., Research Physiologist,
Pacific Medical Center, Seattle, Washington.

Andrea L. Dunn, Ph.D., Associate Director, Division
of Epidemiology and Clinical Applications, The
Cooper Institute for Aerobics Research, Dallas, Texas.

Leonard H. Epstein, Ph.D., Professor, Department of
Psychology, State University of New York at Buffalo,
Buffalo, New York.

Katherine M. Flegal, Ph.D., Senior Research
Epidemiologist, National Center for Health Statistics,
Centers for Disease Control and Prevention,
Hyattsville, Maryland.

Christopher D. Gardner, Ph.D., Research Fellow,
Stanford Center for Research in Disease Prevention,
Stanford University, Palo Alto, California.

Glen G. Gilbert, Ph.D., Professor and Chairperson,
Department of Health Education, University of
Maryland, College Park, Maryland.

Andrew P. Goldberg, M.D., Professor of Medicine
and Director, Division of Gerontology, University of
Maryland School of Medicine, Baltimore, Maryland.

John 0. Holloszy, M.D., Professor of Internal
Medicine, Washingtonuniversity SchoolofMedicine,
St. Louis, Missouri.

Melbourne F. Hovell, Ph.D., M.P.H., Professor of
Health Promotion; Director, Center for Behavioral
Epidemiology, Graduate School of Public Health,
College of Health and Human Services, San Diego
State University, San Diego, California.

xi


A Report of the Surgeon General

Caroline A. Macera, Ph.D., Director, Prevention
Center, School of Public Health, University of South
Carolina, Columbia, South Carolina.

JoAnn E. Manson, M.D., Dr.P.H., Co-Director of
Women's Health, Brigham and Women's Hospital,
Harvard Medical School, Boston, Massachusetts.

Jere H. Mitchell, M.D., Professor of Internal Medicine
and Physiology; Director, Harry S. Moss Heart Center,
University of Texas Southwestern Medical Center,
Dallas, Texas.

James R. Morrow, Jr., Ph.D., Professor and Chair,
Department of KHPR, University of North Texas,
Denton, Texas.

Neville Owen, Ph.D., Professor of Human Movement
Science, Deakin University, Melbourne, Australia.
Roberta J. Park, Ph.D., Professor of the Graduate
School, University of California, Berkeley, California.

Peter B. Raven, Ph.D., Professor and Chair,
Department of Integrative Physiology, University of
North Texas Health Science Center, Fort Worth,
Texas.

Judith G. Regensteiner, Ph.D., Associate Professor of
Medicine, University of Colorado Health Sciences
Center, Denver, Colorado.

Bruce G. Simons-Morton, Ed.D., M.P.H., Behavioral
Scientist, Prevention Research Branch, National
Institute of Child Health and Human Development,
National Institutes of Health, Bethesda, Maryland.

Denise G. Simons-Morton, M.D., Ph.D., Leader,
Prevention Scientific Research Group, DECA,
National Heart, Lung, and Blood Institute, National
Institutes of Health, Bethesda, Maryland.

James S. Skinner, Ph.D., Professor, Department of
Kinesiology, Indiana University, Bloomington,
Indiana.

Thomas Stephens, Ph.D., Principal, Thomas Stephens
and Associates, Ottawa, Canada.

Anita Stewart, Ph.D., Associate Professor in
Residence, University of California, San Francisco,
San Francisco, California.

C. Barr Taylor, M.D., Professor of Psychiatry,
Department of Psychiatry and Behavioral Sciences,
Stanford University School of Medicine, Stanford,
California.

Charles M. Tipton, Ph.D., F.A.C.S.M., Professor of
Physiology and Surgery, University of Arizona,
Tucson, Arizona.

Zung Vu Tran, Ph.D., Senior Research Scientist,
Center for Research in Ambulatory Health Care
Administration, Englewood, Colorado.

Other Contributors

Melissa M. Adams, Ph.D., Assistant Director for
Science, Division of Reproductive Health, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Indu Ahluwalia, M.P.H., Ph.D., EISOfficer, Division
of Nutrition and Physical Activity, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Betty A. Ballinger, Technical Information Specialist,
Technical Information and Editorial Services Branch,
National Center for Chronic Disease Prevention and
Health Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Sandra W. Bart, Policy Coordinator, Office of the
Secretary, Executive Secretariat, Department of
Health and Human Services, Washington, D.C.

Mary Bedford, Proofreader, Cygnus Corporation,
Rockville, Maryland.

Caryn Bern, M.D., Medical Epidemiologist, Division
of Nutrition and Physical Activity, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Karil Bialostosky, M.S., Nutrition Fellow, National
Center for Health Statistics, Centers for Disease
Control and Prevention, Hyattsville, Maryland.

xii


Physical Activity and Health

Thomas E. Blakeney, Program Analyst, National
Center for Injury Prevention and Control, Centers
for Disease Control and Prevention, Atlanta,
Georgia.

Ronctte R. Briefel, Dr.P.H.. Nutrition Policy Advisor,
National Center for Health Statistics, Centers for
Disease Control and Prevention, Hyattsville,
htaryland.

L. Diane Clark, M.P.H., Public Health Nutritionist,
Division of Nutrition and Physical Activity, National
Ccntcr for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

jancl L. Coil' Ins, Ph.D., Chief, Surveillance and
Evaluation Research Branch, Division of Adolescent
and School Health, National Center for Chronic
Disease Prevention and Health Promotion, Centers
for Disease Control and Prevention, Atlanta,
Georgia.

Janet B. Croft, Ph.D.,Epidemiogist,DivisionofAdult
;tnd Community Health, National Center for Chronic
Discasc Prevention and Health Promotion, Centers
for Disease Control and Prevention, Atlanta,
Georgia.

Ann M. Cronin, Program Analyst, National Institute
for Occupational Safety and Health, Centers for
Discase Control and Prevention, Atlanta, Georgia.

(iail A. Cruse, M.L.I.S., Technical Information
Specialist, Technical Information and Editorial
Scrviccs Branch, National Center for Chronic Disease
Prcventionand Health Promotion, Centers for Disease
Control and Prevention, Atlanta, Georgia.

John M. Davis, M.P.A., R.D., Public Health Analyst,
Division of Nutrition and Physical Activity, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Earl S. Ford, M.D., M.P.H., Senior Scientist, Division
of Nutrition and Physical Activity, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Christine S. Fralish, M.L.I.S., Chief, Technical
Information and Editorial Services Branch, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Emma L. Frazier, Ph.D., Mathematical Statistician,
Division of Diabetes Translation, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Deborah A. Galuska, M.P.H., Ph.D., EIS Fellow,
Division of Nutrition and Physical Activity, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Dinamarie C. Garcia, M.P.H., C.H.E.S., Intern,
Division of Nutrition and Physical Activity, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Linda S. Geiss, M.A., Health Statistician, Division of
Diabetes Translation, National Center for Chronic
Disease Prevention and Health Promotion, Centers
for Disease Control and Prevention, Atlanta, Georgia.

Wayne H. Giles, M.D., M.S., Epidemiologist,
Cardiovascular Health Section, Division of Adult
and Community Health, National Center for Chronic
Disease Prevention and Health Promotion, Centers
for Disease Control and Prevention, Atlanta, Georgia.

Kay Sissions Golan, Public Affairs Specialist, Office
of Communication (proposed), Centers for Disease
Control and Prevention, Atlanta, Georgia.

Betty H. Haithcock, Editorial Assistant, Technical
Information and Editorial Services Branch, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Helen P. Hankins, Writer-Editor, Technical
Information and Editorial Services Branch, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

. . .
XIII


A Report of the Surgeon General

Rita Harding, Graphic Designer, Cygnus Corporation,
Rockville, Maryland.

William A. Harris, M.M., Computer Specialist,
Division of Adolescent and School Health, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Charles G. Helmick, III, M.D., Division of Adult and
Community Health, National Center for Chronic
Disease Prevention and Health Promotion, Centers
for Disease Control and Prevention, Atlanta, Georgia.

Elizabeth L. Hess, Technical Editor, Cygnus
Corporation, Rockville, Maryland.

Mary Ann Hill, M.P.P., Director of Communications,
President's Council on Physical Fitness and Sports,
Washington, D.C.

Thomya L. Hogan, Proofreader, Cygnus Corporation,
Rockville, Maryland.

Judy F. Horne, Technical Information Specialist,
Technical Information and Editorial ServicesBranch,
National Center for Chronic Disease Prevention and
Health Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Catherine A. Hutsell, M.P.H., Public Health Educator,
Division of Adult and Community Health, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Robert Irwin, Special Assistant, Office of the Director,
Centers for Disease Control and Prevention,
Washington, D.C.

Sandra E. Jewell, MS., Statistician, Division of
Nutrition and Physical Activity, National Center for
Chronic Disease Prevention and Health Promotion,
Centers for Disease Control and Prevention, Atlanta,
Georgia.

Loretta G. Johnson, Secretary, Division of Nutrition
and Physical Activity, National Center for Chronic
Disease Prevention and Health Promotion, Centers
for Disease Control and Prevention, Atlanta, Georgia.

Deborah A. Jones, Ph.D., Epidemiologist, Division
of Nutrition and Physical Activity, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Wanda K. Jones, M.P.H., Dr.P.H., Associate Director
for Women's Health, Office of Women's Health,
Centers for Disease Control and Prevention, Atlanta,
Georgia.

Robert E. Keaton, Consultant, Cygnus Corporation,
Rockville, Maryland.

Delle B. Kelley, Technical Information Specialist,
Technical Information and Editorial ServicesBranch,
National Center for Chronic Disease Prevention and
Health Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Mescal J. Knighton, Writer-Editor, Technical
Information and Editorial Services Branch, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Sarah B. Knowlton, J.D., M.S.W., Attorney Advisor,
Office of the General Council, Centers for Disease
Control and Prevention, Atlanta, Georgia.

FredKroger,ActingDirector,HealthCommunication,
Office of Communication (proposed), Centers for
Disease Control and Prevention, Atlanta, Georgia.

Sarah A. Kuester, M.P.H., R.D., Public Health
Nutritionist, Division of Nutrition and Physical
Activity, National Center for Chronic Disease
Prevention and Health Promotion, Centers for Disease
Control and Prevention, Atlanta, Georgia.

Becky H. Lankenau, M.S., R.D., M.P.H., Dr.P.H.,
Public Health Nutritionist, Division of Nutrition and
Physical Activity, National Center for Chronic Disease
Prevention and Health Promotion, Centers for Disease
Control and Prevention, Atlanta, Georgia.

Nancy C. Lee, M.D., Associate Director for Science,
Division of Cancer Prevention and Control, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

xiv


Physical Activity and Health

Leandris C. Liburd, M.P.H., Public Health Educator,
Division of Diabetes Translation, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Richard Lowry, M.D., M.S., Medical Epidemiologist,
Division of Adolescent and School Health, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Salvatore J. Lucido, M.P.A., Program Analyst,
National Center for Chronic Disease Prevention and
Health Promotion, Centers for Disease Control and
Prevention, Atlanta,, Georgia.

Gene W. Matthews, Esq., Legal Advisor to CDC and
ATSDR, Office of the General Council, Centers for
Disease Control and Prevention, Atlanta, Georgia.

Urcnda W. Mazzocchi, M.S.L.S., Technical
Information Specialist, Technical Information and
Editorial Services Branch, National Center for
Chronic Disease Prevention and Health Promotion,
Ccntcrs for Disease Control and Prevention, Atlanta,
(icorgia.

Sharon McDonnell, M.D., M.P.H., Medical
Ilpidcmiologist, Division of Nutrition and Physical
:\ctivity, National Center for Chronic Disease
I'rcvcntionand Health Promotion, Centers for Disease
Control and Prevention, Atlanta, Georgia.

Michael A. McGeehin, Ph.D., M.S.P.H., Chief, Health
9udics Branch, Division of Environmental Hazards
and Health Effects, National Center for Environmental
1 icalth, Centers for Disease Control and Prevention,
Atlanta, Georgia.

ZU~UO Mei, M.D., M.P.H. Visiting Scientist, Division
of Nutrition and Physical Activity, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease . Control and
Prcvcntion, Atlanta, Georgia.

lames M. Mendlein, Ph.D., Epidemiologist, Division
of Nutrition and Physical Activity, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
frcvenlion, Atlanta, Georgia.

Robert K. Merritt, M.A., Behavioral Scientist, Office
on Smoking and Health, National Center for Chronic
,Disease Prevention and Health Promotion, Centers
for Disease Control and Prevention, Atlanta,
Georgia.

Gaylon D. Morris, M.P.P., Program Analyst, Office
of Program Planning and Evaluation, Centers for
Disease Control and Prevention, Atlanta, Georgia.

Melba Morrow, M.A., Division Manager, The Cooper
Institute for Aerobics Research, Dallas, Texas.

Marion R. Nadel, Ph.D., Epidemiologist, Division of
Cancer Prevention and Control, National Center for
Chronic Disease Prevention and Health Promotion,
Centers for Disease Control and Prevention, Atlanta,
Georgia.

David E. Nelson, M.D., M.P.H., Medical Officer,
Division of Adult and Community Health, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Reba A. Norman, M.L.M., Technical Information
Specialist, Technical Information and Editorial
Services Branch, National Center for Chronic Disease
Prevention andHealth Promotion, Centers for Disease
Control and Prevention, Atlanta, Georgia.

Ward C. Nyholm, Graphic Designer, Cygnus
Corporation, Rockville, Maryland.

Stephen M. Ostroff, M.D., Associate Director for
Epidemiologic Science, National Center for Infectious
Diseases, Centers for Disease Control and Prevention,
Atlanta, Georgia.

Ibrahim Parvanta, MS., Acting Deputy Chief,
Maternal and Child Health Branch, Division of
Nutrition and Physical Activity, National Center for
Chronic Disease Prevention and Health Promotion,
Centers for Disease Control and Prevention, Atlanta,
Georgia.

Terry F. Pechacek, Ph.D., Visiting Scientist, Office
on Smoking and Health, National Center for Chronic
Disease Prevention and Health Promotion, Centers
for Disease Control and Prevention, Atlanta, Georgia.

xv


A Report of the Surgeon General

Geraldine S. Perry, Dr.P.H., Epidemiologist, Division
of Nutrition and Physical Activity, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Todd M. Phillips, M.S., Deputy Project Director,
Cygnus Corporation, Rockville, Maryland.

Audrey L. Pinto, Writer-Editor, Technical
Information and Editorial Services Branch, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Kenneth E. Powell, M.D., M.P.H., Associate Director
for Science, Division of Violence Prevention, National
Center for Injury Prevention and Control, Centers
for Disease Control and Prevention, Atlanta,Georgia.

Julia H. Pruden, M.Ed., R.D., Public Health
Nutritionist, Division of Nutrition and Physical
Activity, National Center for Chronic Disease
Prevention and Health Promotion, Centers for Disease
Control and Prevention, Atlanta, Georgia.

David C. Ramsey, M.P.H., Public Health Educator,
Division of Nutrition and Physical Activity, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Brenda D. Reed, Secretary, Division of Adult and
Community Health, National Center for Chronic
Disease Prevention and Health Promotion, Centers
for Disease Control and Prevention, Atlanta, Georgia.

Susan A. Richardson, Writer-Editor, Cygnus
Corporation, Rockville, Maryland.

Christopher Rigaux, Project Director, Cygnus
Corporation, Rockville, Maryland.

Angel Rota, Program Analyst, National Center for
Chronic Disease Prevention and Health Promotion,
Centers for Disease Control and Prevention, Atlanta,
Georgia.

Cheryl V. Rose, Computer Specialist, Division of
Health Promotion Statistics, National Center for
Health Statistics,. Centers for Disease Control and
Prevention, Hyattsville, Maryland.

Patti Schwartz, Graphic Designer, Cygnus Corporation,
Rockville, Maryland.

Bettylou Sherry, Ph.D., Epidemiologist, Maternal
and Child Health Branch, Division of Nutrition and
Physical Activity, National Center for Chronic Disease
Prevention and Health Promotion, Centers for Disease
Control and Prevention, Atlanta, Georgia.

Margaret Leavy Small, Behavioral Scientist, Division
of Adolescent and School Health, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia

Joseph B. Smith, Senior Project Officer, Disabilities
Prevention Program, National Center for
Environmental Health, Centers for Disease Control
and Prevention, Atlanta, Georgia.

Terrie D. Sterling, Ph.D., Research Psychologist,
Division of Adult and Community Health, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Emma G. Stupp, M.L.S., Technical Information
Specialist, Technical Information and Editorial
ServicesBranch, National Center for Chronic Disease
Prevention and Health Promotion, Centers for Disease
Control and Prevention, Atlanta, Georgia.

William I. Thomas, M.L.I.S., Technical Information
Specialist, Technical Information and Editorial
Services Branch, National Center for Chronic Disease
Prevention and Health Promotion, Centers for Disease
Control and Prevention, Atlanta, Georgia.

Patricia E. Thompson-Reid, M.A.T., M.P.H.,
Program Development Consultant/Community
Interventionist, Division of Diabetes Translation,
National Center for Chronic Disease Prevention and
Health Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Jenelda Thornton, Staff Specialist, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

xvi


Physical Activity and Health

Nancy B. Watkins, M.P.H., Health Education
Specialist, Division of Adult and Community Health,
National Center for Chronic Disease Prevention and
Health Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Howell Wechsler, Ed.D., M.P.H., Health Education
Research Scientist, Division of Adolescent and School
Health, National Center for Chronic Disease
Preventionand Health Promotion, Centers for Disease
Control and Prevention, Atlanta, Georgia.

Julie C. Will, Ph.D., M.P.H., Epidemiologist, Division
of Nutrition and Physical Activity, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Lynda S. Williams, Program. Analyst, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

David F. Williamson, Ph.D., Acting Director,
Division of Diabetes Translation, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Stephen W. Wyatt, D.M.D., M.P.H., Director, Division
of Cancer Prevention and Control, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia,

Matthew M. Zack, M.D.; M.P.H., Medical
Epidemiologist, Division of Adult and Community
Health, National Center for Chronic Disease
Prevention andHealth Promotion, Centers for Disease
Control and Prevention, Atlanta, Georgia.

xvii


PHYSICAL ACTIVITV AND HEALTH

Chapter 1: Introduction, Summary, and Chapter Conclusions   ....................... 1
Chapter 2: Historical Background, Terminology, Evolution of Recommendations
andbleasurement   .......................................................... 9

Western Historical Perspective  ............................................... .12
Terminology of Physical Activity, Physical Fitness, and Health  ..................... .2O
Evolution of Physical Activity Recommendations  .................................. 22
Summary of Recent Physical Activity Recommendations ........................... .28
Measurement of Physical Activity, Fitness, and Intensity  .......................... .29
Chapter 3: Physiologic Responses and Long-Term Adaptations to Exercise  ............ .61
Physiologic Responses to Episodes of Exercise  .................................. .61
Long-Term Adaptations to Exercise Training .................................... .67
Maintenance, Detraining, and Prolonged Inactivity  ............................... .71
Special Considerations  ..................................................... .73

Chapter 4: The Effects of Physical Activity on Health and Disease  ................... .81
Overall Mortality  ........................................................... .85

  Cardiovascular Diseases  .................................................... .87

  Cancer ................................................................ ..112
Non-Insulin-Dependent Diabetes Mellitus ..................................... .125

  Osteoarthritis                                                .129
                ................. , ..........................................
  Osteoporosis ........................................................... ..13 0
Obcsity..................................................................13 3
  McntalHealth .......................................................... ..13 5
  Health-Related Quality of Life ............................................... .141
  Adverse Effects of Physical Activity  .......................................... .142
  Occurrence of Adverse Effects  .............................................. .144
  Nature of the Activity/Health Relationship  ..................................... .144

Cllaptcr 5: Patterns and Trends in Physical Activity  ............................... 173
  Physical Activity among Adults in the United States  ............................. .177
Physical Activity among Adolescents and Young Adults in the United States  ........... 186

Chapter 6: Understanding and Promoting Physical Activity   ....................... ,209
  Theories and Models Used in Behavioral and Social Research on
   PhysicalActivity.. .................................................... ..211
  Behavioral Research on Physical Activity among Adults  .......................... .215
Behavioral Research on Physical Activity among Children and Adolescents  ........... .234
  Promising Approaches, Barriers, and Resources  ................................. .243
List of Tables and Figures   ................................................... .261

Index  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...265


        CHAPTER 1
INTRODUCTION, SUMMARY,
AND CHAPTER CONCLUSIONS

Contents

Introduction  ................................................................. 3
Development of the Report  ................................................... 3
MajorConclusions  ......................................................... 4

Summary . .._................................................,............._ 4

Chapter Conclusions  .......................................................... 6
Chapter 2: Historical Background and Evolution of Physical Activity Recommendations  . . 6
Chapter 3: Physiologic Responses and Long-Term Adaptations to Exercise  ............. 7
Chapter 4: The Effects of Physical Activity on Health and Disease  .................... 7
Chapter 5: Patterns and Trends in Physical Activity  ............................... 8
Chapter 6: Understanding and Promoting Physical Activity  ......................... 8


CHAPTER 1

htroduction

T his is the first Surgeon General's report to ad-
dress physical activity and health. The main
message of this report is that Americans can substan-
tially improve their health and quality of life by
including moderate amounts of physical activity in
their daily lives. Health benefits from physical activ-
ity arc thus achievable for most Americans, includ-
ing those who may dislike vigorous exercise and
those who may have been previously discouraged by
rhc difficulty of adhering to a program of vigorous
cscrcise. For those who are alreadyachievingregular
modcrate amounts of activity, additional benefits
c.an bc gained by further increases in activity level.
This report grew out of an emerging consensus
:~mong epidemiologists, experts in exercise science,
;1nc1 health professionals that physical activity need
not be of vigorous intensity for it to improve health.
Morcovcr, health benefits appear to be proportional
10 amount of activity; thus, every increase in activity
~lds some benefit. Emphasizing the amount rather
lhan the intensity of physical activity offers more
options for people to select from in incorporating
physical activity into their daily lives. Thus, a mod-
crate amount of activity can be obtained in a 30-
minute brisk walk, 30 minutes of lawn mowing or
raking leaves, a 1%minute run, or 45 minutes of
playing volleyball, and these activities can be varied
from day to day. It is hoped that this different
elnphasis on moderate amounts of activity, and the
ncsibility to vary activities according to personal
prcfcrcnce and life circumstances, will encourage
more people to make physical activity a regular and
sustainable part of their lives.

The information in this report summarizes a
diverse literature from the fields of epidemiology,
cscrcisc physiology, medicine, and the behavioral
sciences. The report highlights what is known about

INTRODUCTION, SUMMARY,
AND CHAPTER CONCLUSIONS

physical activity and health; as well as what is being
learned about promoting phjrsical activity among
adults and young people.

Development of the Report
In July 1994, the Office of the Surgeon General
authorized the Centers for Disease Control and Pre-
vention (CDC) to serve as lead agency for preparing
the first Surgeon General's report on physical activity
and health. The CDC was joined in this effort by the
President's Council on Physical Fitness and Sports
(PCPFS) as a collaborative partner representing the
Office of the Surgeon General. Because of the wide
interest in the health effects of physical activity, the
report was planned collaboratively with representa-
tives from the Office of the Surgeon General, the
Office of Public Health and Science (Office of the
Secretary), the Office of Disease Prevention (Na-
tional Institutes of Health [NIH]), and the following
institutes from the NIH: the National Heart, Lung,
and Blood Institute; the National Institute of Child
Health and Human Development; the National Insti-
tute of Diabetes and Digestive and Kidney Diseases;
and the National Institute of Arthritis and Muscu-
loskeletal and Skin Diseases. CDC's nonfederal part-
ners-indluding the American Alliance for Health,
Physical Education, Recreation, and Dance; the
American College of Sports Medicine; and the Ameri-
can Heart Association-provided consultation
throughout the development process.
The major purpose of this report is to summarize
the existing literature on the role of physical activity in
preventing disease and on the status of interventions to
increase physical activity. Any report on a topic this
broad must restrict its scope to keep its message clear.
This report focuses on disease prevention and there-
fore does not include the considerable body of evi-
dence on the benefits of physical activity for treatment or


Physical Activity and Health

rehabilitation after disease has developed. This report
concentrates on endurance-type physical activity (ac-
tivity involving repeated use of large muscles, such as
in walking or bicycling) because the health benefits of
this type of activity have been extensively studied. The
importance of resistance exercise (to increase muscle
strength, such as by lifting weights) is increasingly
being recognized as a means to preserve and enhance
muscular strength and endurance and to prevent falls
and improve mobility in the elderly. Some promising
findings on resistance exercise are presented here, but
a comprehensive review of resistance training is be-
yond the scope of this report. In addition, a review of the
special concerns regarding physical activity for preg-
nant women and for people with disabilities is not
undertaken here, although these important topics de-
serve more research and attention.
Finally, physical activity is only one of many every-
day behaviors that affect health. In particular, nutri-
tional habits are linked to some of the same aspects of
health as physical activity, and the two may be related
lifestyle characteristics. This report deals solely with
physical activity; a Surgeon General's Report on Nutri-
tion and Health was published in 1988.
  Chapters 2 through 6 of this report address dis-
tinct areas of the current understanding of physical
activity and health. Chapter 2 offers a historical per-
spective: after outlining the history of belief and
knowledge about physical activity and health, the
chapter reviews the evolution and content of physical
activity recommendations. Chapter 3 describes the
physiologic responses to physical activity-both the
immediate effects of a single episode of activity and the
long-term adaptations to a regular pattern of activity.
The evidence that physical activity reduces the risk of
cardiovascular and other diseases is presented in
Chapter 4. Data on patterns and trends of physical
activity in the U.S. population are the focus of Chapter
5. Lastly, Chapter 6 examines efforts to increase
physical activity and reviews ideas currently being
proposed for policy and environmental initiatives.

Major Conclusions
1. People of all ages, both male and female, benefit
from regular physical activity.
2. Significant health benefits can be obtained by
including a moderate amount of physical activity
(e.g., 30 minutes of brisk walking or raking

3.

4.

5.

6.

7.

leaves, 15 minutes of running, or 45 minutes of
playing volleyball) on most, if not all, days of the
week. Through a modest increase in daily activity,
most Americans can improve their health and
quality of life.

Additional health benefits can be gained through
greater amounts of physical activity. People who
can maintain a regular regimen of activity that is
of longer duration or of more vigorous intensity
are likely to derive greater benefit.
Physical activity reduces the. risk of premature
mortality in general, and of coronary heart dis-
ease, hypertension, colon cancer, and diabetes
mellitus in particular. Physical activity also im-
proves mental health and is important for the
health of muscles, bones, and joints.
More than 60 percent of American adults are not
regularly physically active. In fact, 25 percent of
all adults are not active at all.
Nearly half of American youths 12-21 years of age
are not vigorously active on a regular basis. More-
over, physical activity declines dramatically dur-
ing adolescence.

Daily enrollment in physical education classes
has declined among high school students from 42
percent in 1991 to 25 percent in 1995.

8. Research on understanding and promotingphysi-
cal activity is at an early stage, but some interven-
tions to promote physical activity through schools,
worksites, and health care settings have been
evaluated and found to be successful.

Summary

The benefits of physical activity have been extolled
throughout western history, but it was not until the
second half of this century that scientific evidence
supporting these beliefs began to accumulate. By the
1970s enough information was available about the
beneficial effects of vigorous exercise on cardiorespi-
ratory fitness that the American College of Sports
Medicine (ACSM), the American Heart Association
(AHA), and other national organizations began issu-
ing physical activity recommendations to the public.
These recommendations generally focused on car-
diorespiratory endurance and specified sustained
periods of vigorous physical activity involving large
muscle groups and lasting at least 20 minutes on 3 or

4


more days per week. As understanding of the ben-
efitsoflessvigorousactivitygrew, recommendations
followed suit. During the past few years, the ACSM,
the CDC, the AHA, the PCPFS, and the NIH have all
recommended regular, moderate-intensity physical
activity as an option for those who get little or no
exercise. The Healthy Peopfe2OOOgoals for the nation's
health have recognized the importance of physical
activity and have included physical activity goals.
The 1995 Dietary Guidelinesfor Americans, the basis
of the federal government's nutrition-related pro-
grams, included physical activity guidance to main-
tain and improve weight-30 minutes or more of
moderate-intensity physical activity on all, or most,
days of the week.

Underpinning such recommendations is a grow-
ing understanding of how physical activity affects
physiologic function. The body-responds to physical
activity in ways that have important positive effects
on musculoskeletal, cardiovascular, respiratory, and
endocrine systems. These changes are consistent
with a number of health benefits, including a re-
duced risk of premature mortality and reduced risks
of coronary heart disease, hypertension, colon can-
cer, and diabetes mellitus. Regular participation in
physical activity also appears to reduce depression
and anxiety, improve mood, and enhance ability to
perform daily tasks throughout the life span.
The risks associated with physical activity must
also be considered. The most common health prob-
lems that have been associated with physical activity
are musculoskeletal injuries, which can occur with
excessive amounts of activity or with suddenly be-
ginning an activity for which the body is not condi-
tioned. Much more serious associated health
problems (i.e., myocardial infarction, sudden death)
are also much rarer, occurring primarily among
sedentary people with advanced atherosclerotic dis-
ease who engage in strenuous activity to which they
are unaccustomed. Sedentary people, especially those
with preexisting health conditions, who wish to
increase their physical activity should therefore
gradually build up to the desired level of activity.
Even among people who are regularly active, the risk
of myocardial infarction or sudden death is some-
what increased during physical exertion, but their
overall risk of these outcomes is lower than that
among people who are sedentary.

Introduction, Summary, and Chapter Conclusions

  Research on physical activity continues to evolve.
This report includes both well-established findings
and newer research results that await replication and
amplification. Interest has been developing in ways
to differentiate between the various characteristics of
physical activity that improve health. It remains to be
determined how the interrelated characteristics of
amount, intensity, duration, frequency, type, and
pattern of physical activity are related to specific
health or disease outcomes.

Attention has been drawn recently to findings
from three studies showing `that cardiorespiratory
fitness gains are similar when physical activity oc-
curs in several short sessions (e.g., 10 minutes) as
when the same total amount and intensity of activity
occurs in one longer session (e.g., 30 minutes).
Although, strictly speaking, the health benefits of
such intermittent activity have not yet been demon-
strated, it is reasonable to expect them to be similar
to those of continuous activity. Moreover, for people
who are unable to set aside 30 minutes for physical
activity, shorter episodes are clearly better than none.
Indeed, one study has shown greater adherence to a
walking program among those walking several times
per day than among those walking once per day,
when the total amount of walking time was kept the
same. Accumulating physical activity over the course
of the day has been included in recent recommenda-
tions from the CDC and ACSM, as well as from the
NIH Consensus Development Conference on Physi-
cal Activity and Cardiovascular Health.
Despite common knowledge that exercise is
healthful, more than 60 percent of American adults
are not regularly active, and 25 percent of the adult
population are not active at all. Moreover, although
many people have enthusiastically embarked on vig-
orous exercise programs at one time or another, most
do not sustain their participation. Clearly, the pro-
cesses of developing and maintaining healthier hab-
its are as important to study as the health effects of
these habits.

The effort to understand how to promote more
active lifestyles is of great importance to the health of
this nation. Although the study of physical activity
determinants and interventions is at an early stage,
effective programs to increase physical activity have
been carried out in a variety of settings, such as
schools, physicians' offices, and worksites. Determin-
ing the most effective and cost-effective intervention

5


Physical Activity and Health

approaches is a challenge for the future. Fortu-
nately, the United States has skilled leadership and
institutions to support efforts to encourage and
assist Americans to become more physically active.
Schools, community agencies, parks, recreational
facilities, and health clubs are available in most
communities and can be more effectively used in
these efforts.

School-based interventions for youth are particu-
larly promising, not only for their potential scope-
almost all young people between the ages of 6 and 16
years attend school-but also for their potential im-
pact. Nearly half of young people 12-21 years of age
are not vigorously active; moreover, physical activity
sharply declines during adolescence. Childhood and
adolescence may thus be pivotal times for preventing
sedentary behavior among adults by maintaining the
habit of physical activity throughout the school years.
School-based interventions have been shown to be
successful in increasing physical activity levels. With
evidence that success in this arena is possible, every
effort should be made to encourage schools to require
daily physical education in each grade and to promote
physical activities that can be enjoyed throughout life.
  Outside the school, physical activity programs
and initiatives face the challenge of a highly techno-
logical society that makes it increasingly convenient
to remain sedentary and that discourages physical
activity in both obvious and subtle ways. To increase
physical activity in the general population, it may be
necessary to go beyond traditional efforts. This re-
port highlights some concepts from community
initiatives that are being implemented around the
country. It is hoped that these examples will spark
new public policies and programs in other places as
well. Special efforts will also be required to meet the
needs of special populations, such as people with
disabilities, racial and ethnic minorities, people with
low income, and the elderly. Much more informa-
tion about these important groups w-ill be necessary
to develop a truly comprehensive national initiative
for better health through physical activity. Chal-
lenges for the future include identifying key deter-
minants of physically active lifestyles among the
diverse populations that characterize the United
States (including special populations, women, and
young people) and using this information to design
and disseminate effective programs.

Chapter Conclusions
Chapter 2: Historical Background and
Evolution of Physical Activity
Recommendations

1.

Physical activity for better health and well-being
has been an important theme throughout much
of western history.

2.

Public health recommendations have evolved
from emphasizing vigorous activity for cardio-
respiratory fitness to including the option of
moderate levels of activity for numerous health
benefits.

3.

Recommendations from experts agree that for
better health, physical activity should be per-
formed regularly. The most recent recommenda-
tions advise people of all ages to include a
minimum of 30 minutes of physical activity of
moderate intensity (such as brisk walking) on
most, if not all, days of the week. It is also
acknowledged that for most people, greater health
benefits can be obtained by engaging in physical
activity of more vigorous intensity or of longer
duration.

4.

Experts advise previously sedentary people em-
barking on a physical activity program to start
with short durations of moderate-intensity activ-
ity and gradually increase the duration or inten-
sity until the goal is reached.

5.

6

Experts advise consulting with a physician before
beginning a new physical activity program for
people with chronic diseases, such as cardiovas-
cular disease and diabetes mellitus, or for those
who are at high risk for these diseases. Experts
also advise men over age 40 and women over age
50 to consult a physician before they begin a
vigorous activity program.
Recent recommendations from experts also sug-
gest that cardiorespiratory endurance activity
should be supplemented with strength-devel-
oping exercises at least twice per week for
adults, in order to improve musculoskeletal
health, maintain independence in performing
the activities of daily life, and reduce the risk of
falling.

6


Introduction, Summary, and Chapter Conclusions

Chapter 3: Physiologic Responses and Long-
Term Adaptations to Exercise

Physical activity has numerous beneficial physi-
ologic effects. Most widely appreciated are its
effects on the cardiovascular and musculoskel-
eta1 systems, but benefits on the functioning of
metabolic, endocrine, and immune systems are
also considerable.

Many of the beneficial effects of exercise training-
from both endurance and resistance activities-
diminish within 2 weeks if physical activity is
substantially reduced, and effects disappear within
2 to 8 months if physical activity is not resumed.

,. People of all ages, both male and female, undergo
beneficial physiologic adaptations to physical
activity.

Chapter 4: The Effects of Physical Activity
on Health and Disease

Overall Mortality
I. Higher levels of regular physical activity are asso-
ciated with lower mortality rates for both older
and younger adults.
2. Even those who are moderately active on a regu-
lar basis have lower mortality rates than those
who are least active.

Cardiovascular Diseases
1. Regular physical activity or cardiorespiratory fit-
ncss decreases the risk of cardiovascular disease
mortality in general and of coronary heart disease
mortality in particular. Existing data are not con-
clusive regarding a relationship between physical
activity and stroke.

1. The level of decreased risk of coronary heart
disease attributable to regular physical activity is
similar to that of other lifestyle factors, such as
keeping free from cigarette smoking.
3. Regular physical activity prevents or delays the
development of high blood pressure, and exer-
cise reduces blood pressure in people with
hypertension.

Cancer

1. Regular physical activity is associated with a
decreased risk of colon cancer.

2.








3.

There is no association between physical activity
and rectal cancer. Data are too sparse to draw
conclusions regarding a relationship between
physical activity and endometrial, ovarian, or
testicular cancers.

Despite numerous studies on the subject, exist-
ing data are inconsistent regarding an association
between physical activity and breast or prostate
cancers.

Non-Insulin-Dependent Diahefes Mellifus
1.) Regular physical activity lowers the risk of devel-
oping non-insulin-dependent diabetes mellitus.

Osteoarthritis

1. Regular physical activity is necessary for main-
taining normal muscle strength, joint structure,
and joint function. In the range recommended for
health, physical activity is not associated with
joint damage or development of osteoarthritis
and may be beneficial for many people with
arthritis.

2. Competitive athletics may be associated with the
development of osteoarthritis later in life, but
sports-related injuries are the likely cause.

Osteoporosis
1.






2.

Weight-bearing physical activity is essential for
normal skeletal development during childhood
and adolescence and for achieving and maintain-
ing peak bone mass in young adults.
It is unclear whether resistance- or endurance-
type physical activity can reduce the accelerated
rate of bone loss in postmenopausal women in the
absence of estrogen replacement therapy.

Falling

1. There is promising evidence that strength train-
ing and other forms of .exercise in older adults
preserve the ability to maintain independent liv-
ing status and reduce the risk of falling.

Obesif y
1. Low levels of activity, resulting in fewer kilocalo-
ries used than consumed, contribute to the high
prevalence of obesity in the United States.
2. Physical activity may favorably affect body fat
distribution.


Physical Activity and Health

Mental Health

1. Physical activity appears to relieve symptoms of
depression and anxiety and improve mood.
2. Regular physical activity may reduce the risk of
developing depression, although further research
is needed on this topic.

Health-Related Qualify of Life
1. Physical activity appears to improve health-re-
lated quality of life by enhancing psychological
well-being and by improving physical function-
ing in persons compromised by poor health.

Adverse Effects
1. Most musculoskeletal injuries related to physical
activity are believed to be preventable by gradu-
ally working up to a desired level of activity and
by avoiding excessive amounts of activity.
2. Serious cardiovascular events can occur with
physical exertion, but the net effect of regular
physical activity is a lower risk of mortality from
  cardiovascular disease.

Chapter 5: Patterns and Trends
in Physical Activity
Adults

1. Approximately 15 percent of U.S. adults engage
regularly (3 times a week for at least 20 minutes)
in vigorous physical activity during leisure time.
2. Approximately 22 percent of adults engage regu-
larly (5 times a week for at least 30 minutes) in
sustained physical activity of any intensity dur-
ing leisure time.

3. About 25 percent of adults report no physical
activity at all in their leisure time.
4. Physical inactivity is more prevalent amongwomen
than men, among blacks and Hispanics than whites,
among older than younger adults, and among the
less affluent than the more affluent.

5. The most popular leisure-time physical activities
among adults are walking and gardening or yard
work.

Adolescents and Young Adults
1. Only about one-half of U.S. young people (ages
12-21 years) regularly participate in vigorous
physical activity. One-fourth report no vigorous
physical activity.

2. Approximately one-fourth of young people walk
or bicycle (i.e., engage in light to moderate activ-
ity) nearly every day.

3. About 14 percent of young people report no
recent vigorous or light-to-moderate physical
activity. This indicator of inactivity is higher
among females than males and among black
females than white females.

4. Males are more likely than females to participate
in vigorous physical activity, strengthening ac-
tivities, and walking or bicycling.
5. Participation in all types of physical activity de-
clines strikingly as age or grade in school increases.
6. Among high school students, enrollment in physi-
cal education remained unchanged during the
first half of the 1990s. However, daily attendance
in physical education declined from approxi-
mately 42 percent to 25 percent.
7. The percentage of high school students who were
enrolled in physical education and who reported
being physically active for at least 20 minutes in
physical education classes declined from approxi-
mately 81 percent to 70 percent during the first
  half of this decade.

8. Only 19 percent of all high school students report
being physically active for 20 minutes or more in
daily physical education classes.

Chapter 6: Understanding and
Promoting Physical Activity
1. Consistent influences on physical activity pat-
terns among adults and young people include
confidence in one's ability to engage in regular
physical activity (e.g., self-efficacy), enjoyment
of physical activity, support from others, positive
beliefs concerning the benefits of physical activ-
ity, and lack of perceived barriers to being physi-
cally active.
2. For adults, some interventions have been success-
ful in increasing physical activity in communities,
worksites, and health care settings, and at home.
3. Interventions targeting physical education in
elementary school can substantially increasethe
amount of time students spend being physically
active in physical education class.

8


               CHAPTER 2
HISTORICAL BACKGROUND, TERMINOLOGY,
  EVOLUTION OF RECOMMENDATIONS,
           AND MEASUREMENT

Contents

Introduction . . . . ..___..______....................._________................. 11

Western Historical Perspective  ..................................................  12
Early Promotion of Physical Activity for Health .................................. 12
Associating Physical Inactivity with Disease   ....................................  15
Health, Physical Education, and Fitness  ........................................  16
Exercise Physiology Research and Health .......................................  18

Terminology of Physical Activity, Physical Fitness, and Health . . . . . . . . . . . . . . . . . . . . . 20

Evolution of Physical Activity Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Summary of Recent Physical Activity Recommendations . , . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Measurement of Physical Activity, Fitness, and Intensity  ............................. 29
Measuring Physical Activity  ................................................. 29
  Measures Based on Self-Report  ............................................ 29
  Measures Based on Direct Monitoring  ....................................... 31
  Measuring Intensity of Physical Activity  ..................................... 32
  Measuring Physical Fitness  ............................................... 33
     Endurance  .......................................................... 33
     Muscular Fitness  ..................................................... 34
    Body Composition  ................................................... 35
  Validity of Measurements  ................................................ 35

Chaptersummary . .._._.................................................... . . 37


Contents, continued

Conclusions . . . .._.._.____.................................................. 37

References . . . . . . . . . . . . . . . . .._..._....._._...............___._............... 37

Appendix A: Healthy People 2000 Objectives _ . . . . . . . . . . . . . . . _ _ _ _ . . . . . . . . . . .-. 47

Appendix B: NIH Consensus Conference Statement  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _ . . 50


               CHAPTER 2
HISTORICAL BACKGROUND, TERMINOLOGY,
  EVOLUTION OF RECOMMENDATIONS,

AND MEASUREMENT

Introduction

The exercise boom is notjust afad; it is a return
to `nutwrul' activity-the kind for which our
bociics are engineered and whichfacilitates the
proper/unction of our biochemistry and physi-
ology. Viewed through the perspective ofevolu-
tiotmry time, sedentary existence, possible for
grcut numbers of people only during the lust
century, represents a transient, unnatural uber-
ration. (Eaton,Shostak, Konner 1988, p. 168)

T hischapter examines the historical development
of physical activity promotion as a means to
improve health among entire populat,ions. The chap-
tcr focuses on Western (i.e., Greco-Roman) history,
bccausc of the near-linear development of physical
activity promotion across those times and cultures
Icading to current American attitudes and guidelines
regarding physical activity. These guidelines are
discussed in detail in the last half of the chapter. To
Ilcsh out this narrow focus on Western traditions, as
well as to provide a background for the promotional
emphasis of the chapter, this chapter begins by
briefly outlining both anthropological and historical
evidence of the central, "natural" role of physical
activity in prehistoric cultures. Mention is also made
of the historical prominence of physical activity in
non-Greco-Roman cultures, including those of China,
India, Africa, and precolonial America.

Xrchaeologists working in conjunction withmedi-
Cal anthropologists have established that our ances-
tors up through the beginning of the Industrial
Revolution incorporated strenuous physical activity
as a normal part of their daily lives-and not only for
the daily, subsistence requirements of their "work"
.li\cs. Investigations of preindustrial societies still

intact today confirm that physical capability was not
just a grim necessity for success at gathering food and
providing shelter and safety (Eaton, Shostak, Konner
1988). Physical activity was enjoyed throughout every-
day prehistoric life, as an integral component of
religious, social, and cultural expression. Food sup-
plies for the most part were plentiful, allowing ample
time for both rest and recreational physical endeavors.
Eaton, Shostak, and Konner (1988) describe a
"Paleolithic rhythm" (p. 32) observed among con-
temporary hunters and gatherers that seems to
mirror the medical recommendations for physical
activity in this report. This natural cycle of regu-
larly intermittent activity was likely the norm for
most of human existence. Sustenance preoccupa-
tions typically were broken into l- or 2-day periods
of intense and strenuous exertion, followed by l- or
2-day periods of rest and celebration. During these
rest days, however, less intense but still strenuous
exertion accompanied 6- to 20-mile round-trip vis-
its to other villages to see relatives and friends and
to trade with other clans or communities. There or
at home, dancing and cultural play took place.
As the neolithic Agricultural Revolution allowed
more people to live in larger group settings and
cities, and as the specialization of occupations re-
duced the amount and intensity of work-related
physical activities, various healers and philosophers
began to stress that long life and health depended on
preventing illnesses through proper diet, nutrition,
and physical activity. Such broad prescriptions for
health, including exercise recommendations, long
predate the increasingly specific guidelines of classi-
cal Greek philosophy and medicine, which are the
predominant historical focus of this chapter.


Physical Activity and Health

In ancient China as early as 3000 to 1000 B.C.,
the classic Yellow Emperor's Book ojlnternal Medicine
(Huang Ti 1949) first described the principle that
human harmony with the world was the key to
prevention and that prevention was the key to long
life (Shampo and Kyle 1989). These principles grew
into concepts that became central to the 6th century
Chinese philosophy Taoism, where longevity through
simple living attained the status of a philosophy that
has guided Chinese culture through the present day.
tai chi chuan, an exercise system that teachesgraceful
movements, began as early as 200 B.C. with Hua T'o
and has recently been shown to decrease the incidence
of falls in elderly Americans (Huard and Wong 1968;
see Chapter 4).

In India, too, proper diet and physical activity
were known to be essential principles of daily
living. The Ajur Veda, a collection of health and
medical concepts verbally transmitted as early as
3000 B.C., developed into Yoga, a philosophy that
included a comprehensively elaborated series of
stretching and flexibility postures. The principles
were first codified in 600B.C. in the Upanishads and
later in the Yoga Sutras by Patanjali sometime be-
tween 200 B.C. and 200 A.D. Yoga philosophies
also asserted that physical suppleness, proper breath-
ing, and diet were essential to control the mind and
emotions and were prerequisites for religious ex-
perience. In both India and China during this
period, the linking of exercise and health may
have led to the development of a medical subspe-
cialty that today would find its equivalent in sports
medicine (Snook 1984).

Though less directly concerned with physical
health than with social and religious attainment,
physical activity played a key role in other ancient
non-Greco-Roman cultures. In Africa, systems of
flexibility, agility, and endurance training not only
represented the essence of martial arts capability
but also served as an integral component bf reli-
gious ritual and daily life. The Sambuiu and the
Masai of Kenya still feature running as a virtue of
the greatest prowess, linked to manhood and social
stature.

Similarly, in American Indian cultures, running
was a prominent feature of all major aspects of life
(Nabokov 1981). Long before the Europeans in-
vaded, Indians ran to communicate, to fight, and to

hunt. Running was also a means for diverse Ameri-
can Indian cultures to enact their myths and thereby
construct a tangible link between themselves and
both the physical and metaphysical worlds. Among
the Indian peoples Nabokov cites are the Mesquakie
of Iowa, the Chemeheuvi of California, the Inca of
Peru, the Zuni and other Pueblo peoples of the
American Southwest, and the Iroquois of the Ameri-
can East, who also developed the precursor of mod-
ern-day lacrosse. Even today, the Tarahumarahe of
northern Mexico play a version of kickball that
involves entire villages for days at a.time (Nabokov
1981; Eaton, Shostak, Konner 1988).

Western Historical Perspective

Besides affecting the practice of preventive hygiene
(as is discussed throughout this section), the ancient
Greek ideals of exercise and health have influenced
the attitudes of modern western culture toward
physical activity. The Greeks viewed great athletic
achievement as representing both spiritual and
physical strength rivaling that of the gods (Jaeger
1965). In the classical-era Olympic Games, the Greeks
viewed the winners as men who had the character
and physical prowess to accomplish feats beyond the
capability of most mortals. Although participants in
the modern Olympic Games no longer compete with
the gods, today's athletes inspire others to be physi-
cally active and to realize their potential-an inspi-
ration as important for modern peoples as it was for
the ancient Greeks.

Early Promotion of
Physical Activity for Health
Throughout much of recorded western history, phi-
losophers, scientists, physicians, and educators have
promoted the idea that being physically active con-
tributes to better health, improved physical func-
tioning, and increased longevity. Although some of
these claims were based on personal opinions or
clinical judgment, others were the result of system-
atic observation.

Among the ancient Greeks, the recognition that
proper amounts of physical activity are necessary for
healthy living dates back to at least the 5th century
B.C. (Berryman 1992). The lessons found in the

12


Historical Background, Terminology, Evolution of Recommendations, and Measurement

..lalVs of health" taught during the ancient period
sound familiar lo us today: to breathe fresh air, eat
prc>pcr foods, drink the right beverages, take plenty
L,f cscrcise, get the proper amount of sleep, and
inciudc our emotions when analyzing our overall
\vcll-being.

\vcstern historians agree that the close connec-
tlon hctween exercise and medicine dates back to
lhrcc Greek physicians-Herodicus (ca. 480 B.C.),
Hippocrates (ca. 460-ca. 377 B.C.), and Galen
(/I.D. 129-ca. 199). The first to study therapeutic
$~ll~n:~stics--or gymnastic medicine, as it was often
caitcd-was the Greek physician and former exer-
cisc instructor, Herodicus. His dual expertise united
rhc gymnastic with the medical art, thereby prepar-
ing the way for subsequent Greek study of the health
hcncfits of physical activity.
Although Hippocrates is generally known as the
father of preventive medicine, most historians credit
I Icroclicus as the influence behind Hippocrates' in-
lcrcst in the hygienic usesofexerciseanddiet (Cyriax
1~ 1-t; Prccope 1952; Licht 1984; Olivova 1985).
K~~gimcn, the longer of Hippocrates' two works deal-
111g with hygiene, was probably written sometime
mend 400 B.C. In Book 1, he writes:

Eafing alone will not keep a man well; he must
also take exercise. Forfoodand exercise, white
posscssingoppositequalities,yet work together
IO produce health. For it is the nature ofexer-
cisc to USC up material, but offood and drink to
mokc good dejiciencies. And it is necessary, as
il clppcars, to discern the power of various
cxcrcises, both natural exercises andartificial,
to know which of them tends to increaseflesh
cold which to lessen it; and not only this, but
&o to proportion exercise to bulk offood, to
the constitution of the patient, to the age ofthe
i~ldividual, to the season of the year, to the
chclngcs in the winds, to the situation of the
region in which the patient resides, and to the
CoMilu~ion of the year. (1953 reprint, p. 229)
Hippocrates was a major influence on the career
of Claudius Galenus, or Galen, the Greek physician
lvllo wrote numerous works of great importance to
lncdical history during the second century. Of these
.\rorks, his book entitled On Hygiene contains the
lllost information on the healthfulness of exercise.

Whether by sailing, riding on horseback, or driving,
or via cradles, swings, and arms, everyone, even
infants, Galen said, needed exercise (Green 1951
trans., p. 25). He further stated:

The uses of exercise, I think, are twofold, one
for the evacuation ofthe excrements, the other
for the production ofgood condition ofthefit-m
parts oJthe body. For since vigorous motion is
exercise, it must needs be that only these three
things result from it in the exercising body-
hardness of the organs from mutual attrition,
increase of the intrinsic warmth, and acceler-
ated movement of respiration. These are fol-
lowed by all the other individual benefits which
accrue to the bodyfrom exercise;from hardness
of the organs, both insensitivity and strength
forfunction; from warmth, both strongatlrac-
tion for things to be eliminated, readier me-
tabolism, and better nutrition and diffusion of
all substances, whereby it results that solidsare
softened, liquids diluted, and ducts dilated.
And from the vigorous movement of respira-
tion the ducts must be purged and the excre-
ments evacuated. (p. 54)

The classical notion that one could improve
one's health through one's own actions-for ex-
ample, through eating right and getting enough sleep
and exercise -proved to be a powerful influence on
medical theory as it developed over the centuries.
Classical medicine had made it clear to physicians
and the lay public alike that responsibility for disease
and health was not the province of the gods. Each
person, either independently or in counsel with his
or her physician, had a moral duty to attain and
preserve health. When the Middle Ages gave way to
the Renaissance, with its individualistic perspective
and its recovery of classical humanistic influences,
this notion of personal responsibility acquired even
greater emphasis. Early vestiges of a "self-help"
movement arose in western Europe in the 16th
century. As that century progressed, "laws of bodily
health were expressed as value prescriptions" (Burns
1976, p. 208).

More specifically, "orthodox Greek hygiene,"
as Smith (1985, p. 257) called it, flourished as part
of the revival of Galenic medicine as early as the
13th century. The leading medical schools of the


Physical Activity and Health

world--Italy's Salerno, Padua, and Bologna-taught
hygiene to their students as part of general instruc-
tion in the theory and practice of medicine The
works of Hippocrates and Galen dominated a sys-
tem whereby "the ultimate goal was to be able to
practise medicine in the manner of the ancient
physicians" (Bylebyl 1979, p. 341).
Hippocrates' Regimen also became important
during the Renaissance in a literature that Gruman
(1961) identified as "prolongevity hygiene" and de-
fined as "the attempt to attain a markedly increased
longevity by means of reforms in one's way of life"
(p. 221). Central to this literature was the belief that
persons who decided to live a temperate life, espe-
cially by reforming habits of diet and exercise, could
significantly extend their longevity. Beginning with
the writings of Luigi Cornaro in 1558, the classic
Greek preventive hygiene tradition achieved increas-
ing attention from those wishing to live longer and
healthier lives.

Christobal Mendez, who received his medical
training at the University of Salamanca, was the
author of the first printed book devoted to exercise,
Book of Bodily Exercise (1553). His novel and com-
prehensive ideas preceded developments in exercise
physiology and sports medicine often thought to be
unique to the early 20th century. The book consists
of four treatises that cover such topics as the effects
of exercise on the body and on the mind. Mendez
believed, as the humoral theorists did, that the phy-
sician had to clear away excess moisture in the body.
Then, after explaining the ill effects of vomiting,
bloodletting, purging, sweating, and urination, he
noted that "exercise was invented and used to clean
the body when it was too full of harmful things. It
cleans without any of the above-mentioned inconve-
nience and is accompanied by pleasure and joy (as
we will say). If we use exercise under the conditions
which we will describe, it deserves lofty' praise as a
blessed medicine that must be kept in high esteem"
(1960 reprint, p. 22).

In 1569, Hieronymus Mercurialis' The Art of
Gymnastics Among the Ancients was published in
Venice. Mercurialis quoted Galen extensivly and
provided a descriptive compilation of ancient mate-
rial from nearly 200 works by Greek and Roman
authors. In general, Mercurialis established the fol-
lowing exercise principles: people who are ill should

not be given exercise that might aggravate existing
conditions; special exercises should be prescribed on
an individual basis for convalescent, weak, and older
patients; people who lead sedentary lives need ex-
ercise urgently; each exercise should preserve the
existing healthy state; exercise should not disturb
the harmony among the principal humors; exercise
should be suited to each part of the body; and all
healthy people should exercise regularly.
Although Galenism and the humoral theory of
medicine were displaced by new ideas, particularly
through the study of anatomy and physiology, the
Greek principles of hygiene and regimen continued
to flourish in 18th century Europe. For some 18th
century physicians, such nonintervention tactics were
practical alternatives to traditional medical therapies
that employed bloodletting and heavy dosing with
compounds of mercury and drugs-"heroic" medi-
cine (Warner 1986), in which the "cure" was often
worse than the disease.

George Cheyne's An Essay ofHealth and Long LiJe
was published in London in 1724. By 1745, it had
gone through 10 editions and various translations.
Cheyne recommended walking as the "most natural"
and "most useful" exercise but considered riding on
horseback as the "most manly" and "most healthy"
(1734 reprint, p. 94). He also advocated exercises in
the open air, such as tennis and dancing, and recom-
mended cold baths and the use of the "flesh brush"
to promote perspiration and improve circulation.
John Wesley's Primitive Physic, first published in
1747, was influenced to a large degree by George
Cheyne. In his preface, Wesley noted that "the power
of exercise, both to preserve and restore health, is
greater than can well be conceived; especially in
those who add temperance thereto" (1793 reprint,
p. iv). William Buchan's classic Domestic Medicine,
written in 1769, prescribed proper regimen for im-
proving individual and family health. The book
contained rules for the healthy and the sick and
stressed the importance ofexercise for good health in
both children and adults.

During the 19th century, both the classical Greek
tradition and the general hygiene movement were
finding their way into the United States through
American editions of western European medical
treatises or through books on hygiene written by
American physicians. The "self-help" era was also in

14


full bloom during antebellum America. Early ves-
tiges of a self-help movement had arisen in western
Europe in the 16th century. AS that century pro-
grcssed, .&laws of bodily health were expressed as
\aluc prescriptions " (Burns 1976, p. 208). Classical
Greek preventive hygiene was part of formal medical
training through the 18th century and continued on
in the American health reform literature for most of
the 19th century. During the latter period, an effort
~`as made to popularize the Greek laws of health, to
lrlilkc each person responsible for the maintenance
;lnd balance of his or her health. Individual reform
lvritcrs thus wrote about self-improvement, self-
regulation, the responsibility for personal health,
;~nd self-management (Reiser 1985). Ifpeople ate too
much, slept too long, or did not get enough exercise,
they could only blame themselves for illness. By the
3ilmt` token, they could also determine their own
good health (Cassedy 1977; Numbers 1977;
Vcrhrugge 1981; Morantz 1984).
A.F.M. Willich's Lectures on Diet and Regimen
( 1801) emphasized the necessity of exercise within
lhc hounds of moderation. He included information
OII specific exercises, the time for exercise, and the
duration of exercise. The essential advantages of
cscrcisc included increased bodily strength, improved
circulation of the blood and all other bodily fluids,
Cl in necessary secretions and excretions, help in
clearing and refining the blood, and removal of
obstructions.

John Gunn's classic Domestic Medicine, Or Poor
.HuII's Friend, was first published in 1830. His section
c*ntitlcd "Exercise" recommended temperance, exer-
cisc, and rest and valued nature's way over tradi-
lional medical treatment. He also recommended
cscrcise for women and claimed that all of the
"diseases of delicate women" like "hysterics and
hypochondria, arise from want of due exercise in the
open, mild, and pure air" (1986 reprint; p. 109).
Fill:$`, in an interesting statement fdr the 1830s if
IlOt the 199Os, Gunn recommended a training sys-
`cln for all: "The advantages of the training systems
:\rc not confined to pedestrians or walkers-or to
Pugilists or boxers alone; or to horses which are
trained for the chase and the race track; they extend
10 man in all conditions; and were training intro-
duced into the United States, and made use of by
physicians in many cases instead of medical drugs,

Historical Background, Terminology, Evolution of Recommendations, and Measurement

the beneficial consequences in the cure of many
diseases would be very great iFed" (p. 113).

Associating Physical Inactivity with Disease
Throughout history, numerous health professionals
have observed that sedentary people appear to suffer
from more maladies than active people. An early
example is found in the writings of English physician
Thomas Cogan, author of TheHavenofHealth (1584);
he recommended his book to students who, because
of their sedentary ways, were Gelieved to be most
susceptible to sickness.

In his 1713 book Diseases of Workers, Bernar-
dino Ramazzini, an Italian physician considered the
father of occupational medicine, offered his views on
the association between chronic inactivity and poor
health. In the chapter entitled "Sedentary Workers
and Their Diseases," Ramazzini noted that "those
who sit at their work and are therefore called `chair-
workers,' such as cobblers and tailors, suffer from
their own particular diseases." He concluded that
"these workers . . _ suffer from general ill-health and
an excessive accumulation of unwholesome humors
caused by their sedentary life," and he urged them to
at least exercise on holidays "so to some extent
counteract the harm done by many days of sedentary
life" (1964 trans., pp. 281-285).
Shadrach Ricketson, a New York physician, wrote
the first American text on hygiene and preventive
medicine (Rogers 1965). In his 1806 book Means of
Preserving Health and Preventing Diseases, Ricketson
explained that "a certain proportion of exercise is not
much less essential to a healthy or vigorous constitu-
tion, than drink, food, and sleep; for we see that
people, whose inclination, situation, or employ-
ment does not admit of exercise, soon become pale;
feeble, and disordered." He also noted that "exercise
promotes the circulation of the blood, assists diges-
tion, and encourages perspiiation" (pp. 152-153).
Since the 186Os, physicians and others had
been attempting to assess the longevity of runners
and rowers. From the late 1920s (Dublin 1932;
Montoye 1992) to the landmark paper by Morris
and colleagues (1953), observations that prema-
ture mortality is lower among more active persons
than sedentary persons began to emerge and were
later replicated in a variety of settings (Rook 1954;

15


Physical Activity and Health

Brown et al. 1957; Pomeroy and White 1958; Zukel
et al. 1959). The hypothesis that a sedentary lifestyle
leads to increased mortality from coronary heart
disease, as well as the later hypothesis that inactiv-
ity leads to the development of some other chronic
diseases, has been the subject of numerous studies
that provide the major source of data supporting
the health benefits of exercise (see Chapter 4).

Health, Physical Education, and Fitness
The hygiene movement found further expression in
19th century America through a new literature de-
voted to "physical education." In the early part of the
century, many physicians began using the term in
journal articles, speeches, and book titles to describe
the task of teaching children the ancient Greek "laws
of health." As Willich explained in his Lectures on Diet
and Regimen (1801), "by physical education is meant
the bodily treatment of children; the term physical
being applied in opposition to mord (p. 60). In his
section entitled "On the Physical Education of Chil-
dren," he continued to discuss stomach ailments,
bathing, fresh air, exercise, dress, and diseases of the
skin, among other topics. Physical education, then,
implied not merely exercising the body but also
becoming educated about one's body.
These authors were joined by a number of early
19th century educators. For example, an article
entitled "Progress of Physical Education" (1826),
which appeared in the first issue of American journal
of Education, declared that "the time we hope is
near, when there will be no literary institution
unprovided with the proper means to healthful
exercise and innocent recreation, and when literary
men shall cease to be distinguished by a pallid
countenance and a wasted body" (pp. 19-20). Both
William Russell, who was the journal's editor, and
Boston educator William Fowler believed that girls
as well as boys should have ample outdoor exercise.
Knowledge about one's body also was deemed cru-
cial to a well-educated and healthy individual by
several physicians who, as Whorton has suggested,
"dedicated their careers to birthing the modern
physical education movement" (p. 282).
  Charles Caldwell held a prominent position in
Lexington, Kentucky's, Transylvania University
Medical Department. Although he wrote on a variety
of medical topics, his Thoughts on Physical Education

in 1834 gained him national recognition. Caldwell
defined physical education as "that scheme of train-
ing, which contributes most effectually to the devel-
opment, health, and perfection of living matter. As
applied to man, it is that scheme which raises his
whole system to its summit of perfection. . . . Physical
education, then, in its philosophy and practice, is of
great compass. If complete, it would be tantamount
to an entire system of Hygeiene. It would embrace
every thing, that, by bearing in any way on the
human body, might injure or benefit it in its health,
vigor, and fitness for action" (pp. 28-29).
During the first half of the 19th century, systems
of gymnastic and calisthenic exercise that had been
developed abroad were brought to the United States.
The most influential were exercises advanced by Per
Henrik Ling in Sweden in the early 1800s and the
"German system" of gymnastic and apparatus exer-
cises that was based on the work of Johan Christoph
GutsMuths and Friedrich LudwigJahn. Also, Ameri-
cans like Catharine Beecher (1856) and Dioclesian
Lewis (1883) devised their own extensive systems of
calisthenic exercises intended to benefit both women
and men. By the 187Os, American physicians and
educators frequently discussed exercise and health.
For example, physical training in relation to health
was a regular topic in the Boston Medical and Surgical
Journal from the 1880s to the early 1900s.
Testing of physical fitness in physical education
began with the extensive anthropometric documen-
tation by Edward Hitchcock in 1861 at Amherst
College. By the 188Os, Dudley Sargent at Harvard
University was also recording the bodily measure-
ments of college students and promoting strength
testing (Leonard and Affleck 1947). During the early
19OOs, the focus on measuring body parts shifted to
tests of vital working capacity. These tests included
measures of blood pressure (McCurdy 1901;
McKenzie 1913), pulse rate (Foster 1914), and fa-
tigue (Storey 1903). As early as 1905, C. Ward
Crampton, former director of physical training and
hygiene in New York City, published the article "A
Test of Condition" in Medical News. Attempts to
assess physical fitness had constituted a significant
aspect of the work of turn-of-the-century physical
educators, many of whom were physicians.
  Allegations that American conscripts during
World War I were inadequately fit to serve their

16


countq helped shift the emphasis of physical educa-
tion from health-related exercise to performance out-
c`omcs. Public concern stimulated legislation to make
ph\.r;ical education a required subject in schools. But
the financial austerities of the Great Depression had a
neg;ltive effect on education in general, including
physical education (Rogers 1934). At the same time,
the combination of increased leisure time for many
;\mericans and a growing national interest in college
;md high school sports shifted the emphasis on physi-
(al education away from the earlier aim of enhancing
performance and health to a new focus on sports-
related skills and the worthy use of leisure time.
physical efficiency was a term widely used in
the literature of the 1930s. Another term, physical
condition, also found its way into research reports.
111 1936, Arthur Steinhaus published one of the
carlicst articles on "physical fitness" in thejournal
(I\- ffctrld~, Pllysical Education, and Recreation; in
1038, C. H. McCloy's article "Physical Fitness and
<;itizenship" appeared in the same journal.
  As the United States entered World War II, the
Icdcral government showed increasing interest in
physical education, especially toward physical fit-
ucss testing and preparedness. In October 1940,
President Franklin Roosevelt named John Kelly, a
lormcr Olympic rower, to the new position of
national director of physical training. The follow-
i ng year, Fiorella La Guardia, the Mayor of New
York City and the director of civilian defense for the
I'cdcral Security Agency, appointed Kelly as assis-
tant in charge of physical fitness; tennis star Alice
Marble was also chosen to promote physical fitness
among girls and women (Park 1989; Berryman
1995).

In 1943, Arthur Steinhaus chaired a committee
ilppointed by the Board of Directors of the American
Medical Association to review the nature and role of
exercise in physical fitness (Steinhaus et al. 1943),
and C. Ward Crampton chaired a committee on
Physical fitness under the direction'of the Federal
Security Agency. Crampton and his 73-member
advisory council were charged with developingphysi-
~a1 fitness in the civilian population (Crampton 1941;
Park 1989).

In 1941, Morris Fishbein, editor of theJournal of
the American Medical Association, stated that "from
the point of view on physical fitness we are a far

better nation now than we were in 1917," but he
cautioned Americans not to believe "we have at-
tained an optimum in physical fitness" (p. 54). He
realized the magnitude of the fitness problem when
he noted that the poor results of physical examina-
tions reported by the Selective Service Boards were "a
challenge to the medical profession, to the social
scientists, the physical educators, the public health
officials, and all those concerned in the United States
with the physical improvement of our population"
(p. 55). The goals most frequently cited for physical
education between 1941 and 1945 were resistance to
disease, muscular strength and endurance, cardio-
respiratory endurance, muscular growth, flexibility,
speed, agility, balance, and accuracy (Larson and
Yocom 1951).

After World War II concluded, a continuing
interest in physical fitness convinced other key mem-
bers of the medical profession and the American
Medical Association to continue studying exercise.
Much of this interest can be attributed to the pioneer-
ing work of Thomas K. Cureton, Jr., and his Physical
Fitness Research Laboratory at the University of Illinois
(Shea 1993). Cardiologists, health education special-
ists, and physicians in preventive medicine were be-
coming aware of the contributions of exercise to the
overall health and efficiency of the heart and circula-
tory system. In 1946, the American Medical
Association's Bureau of Health Education designed
and organized the Health and Fitness Program to
provide "assistance to local organizations throughout
the nation in the development of satisfactory health
education programs" (Fishbein 1947, p. 1009). The
program became an important link among physical
educators, physicians, and physiologists.
The event that attracted the most public attention
to physical fitness, including that of President Dwight
D. Eisenhower, was the publication of the article
"Muscular Fitness and Health" in the December 1953
issue of the Journal of Health, Physical Education,
and Recreation. The authors, Hans Kraus and Ruth
Hirschland of the Institute of Physical Medicine
and Rehabilitation at the New York University
Bellevue Medical Center, stated that 56.6 per-
cent of the American schoolchildren tested "failed
to meet even a minimum standard required for
health" (p. 17). When this rate was compared with
the 8.3 percent failure rate for European children, a

Historical Background, Terminology, Evolution of Recommendations, and Measurement

17


Physical Activity and Health

call for reform went out. Kraus and Hirschland
labeled the lack of sufficient exercise "a serious
deficiency comparable with vitamin deficiency" and
declared "an urgent need" for its remedy (pp. 17-19).
John Kelly, the former national director of physical
fitness during World War II, notified Pennsylvania
Senator James Duff of these startling test results.
Duff, in turn, brought the research to the attention of
President Eisenhower, who invited several athletes
and exercise experts to a meeting in 1955 to examine
this issue in more depth. A President's Conference
on Fitness of American Youth, held in June 1956,
was attended by 150 leaders from government, physi-
cal education, medical, public health, sports, civic,
and recreational organizations. This meeting even-
tually led to the establishment of the President's
Council on Youth Fitness and the President's Citizens
Advisory Committee on the Fitness of American
Youth (Hackensmith 1966; Van Dalen and Bennett
1971).

When John Kennedy became president in 1961,
one of his first actions was to call a conference on
physical fitness and young people. Iri 1963, the
President's Council on Youth Fitness was renamed
the President's Council on Physical Fitness. In 1968,
the word "sports" was added to the name, making it
the President's Council on Physical Fitness and Sports
(PCPFS). The PCPFS was charged with promoting
physical activity, fitness, and sports for Americans of
all ages.

During the 1960% a number of educational and
public health organizations published articles and
statements on the importance of fitness for children
and youths. The American Association for Health,
Physical Education, and Recreation (AAHPER) ex-
panded its physical fitness testing program to in-
clude college-aged men and women. The association
developed new norms from data collected from more
than 11,000 boys and girls lo-17 years old. The
AAHPER also joined with the President's Cduncil on
Physical Fitness to conduct the AAHPER Youth
Fitness Test, which had motivational awards. In
1966, President Lyndon Johnson's newly created
Presidential Physical Fitness Award was incorpo-
rated into the program.

In the mid-1970s, the need to promote the health-
rather than exclusively the performance-benefits of
exercise and physical fitness began to reappear. In

1975, AAHPER stated it was time to differentiate
physical fitness related to health from performance
related to athletic ability (Blair, Falls, Pate 1983).
Accordingly, AAHPER commissioned the develop-
ment of the Health Related Physical Fitness Test. This
move in youth fitness paralleled the adoption of the
aerobic concept, which promoted endurance-type
exercise among the public (Cooper 1968).

Exercise Physiology Research and Health
The study of the physiology of exercise in a modern
                             r
sense began in Paris, France, when Antoine Lavoisier
in 1777 and Lavoisier and Pierre de Laplace in 1780
developed techniques to measure oxygen uptake and
carbon dioxide production at rest and during exer-
cise. During the 18OOs, European scientists used and
advanced these procedures to study the metabolic
responses to exercise (Scharling 1843; Smith 1857;
Katzenstein 1891; Speck 1889; Allen and Pepys
1809). The first major application of this research to
humans-Edward Smith's study of the effects of
"assignment to hard labor" by prisoners in London
in 1857-was to determine if hard manual labor
negatively affected the health and welfare of the
prisoners and whether it should be considered cruel
and unusual punishment.

William Byford published "On the Physiology of
Exercise" in the American Journal of Medical Sciences
in 1855, and Edward Mussey Hartwell, a leading
physical educator, wrote a two-part article, "On the
Physiology of Exercise, " for the Boston Medical and
SurgicalJournal in 1887. The first important book on
the subject, George Kolb's Beitrage zur Physiologic
Maximaler Muskelarbeit Besondersdes ModemenSports,
was published in 1887 (trans. Physiology of Sport,
1893) (cited in Langenfeld 1988 and Park 1992). The
followingyear,FernandLagrange'sPhysiology ofBodily
Exercise was published in France.
From the early 1900s to the early 192Os, several
works on exercise physiology began to appear. George
Fitz, who had established a physiology of exercise
laboratory during the early 189Os, published his
Principles of Physiology and Hygiene in 1908. R. Tait
McKenzie's Exercise in Education and Medicine (1909)
was followed by such works as Francis Benedict and
Edward Cathcart's Muscular Work, A Metabolic Study
with Special Reference to the Efficiency of the Human
Body as a Machine (1913). The next year, a professor

18


of physiology at the University of London, F.A.
Bainbridge, published a second edition of Physiology
(,I- .tlllscular Exercise (Park 1981).
In 1923, the year Archibald Hill was appointed
]oddrell Professor of Physiology at University Col-
lege, London, the physiology of exercise acquired
ot,c of its most respected researchers and staunchest
supporters, for Hill had won the Nobel Prize in
\Iedicine and Physiology the year before. Hill's 1925
prcsidcntial address on "The Physiological Basis of
*Athletic Records" to the British Association for the
;\dvancement of Science appeared in The Lancel
( I925a) and Scientgic Monthly (1925b), and in 1926
he published his landmark book Muscular Activity.
The following year, Hill published Living Machinery,
Lvhich was based largely on his lectures before audi-
I'IICCS at the Lowell Institute in Boston and the Baker
Laboratory of Chemistry in Ithaca, New York.
  Several leading physiologists besides Hill were
Intcrcstcd in the human body's response to exercise
ant1 cnvironmcntal stressors, especially activities
involving endurance, strength, altitude, heat, and
l~~lcl. Consequently, they studied soldiers, athletes,
;rvlators, and mountain climbers as the best models
lor acquiring data. In the United States, such re-
\c;lrch was centered in the Boston area, first at the
<:arncgic Nutrition Laboratory in the 1910s and
I;trcr at the Harvard Fatigue Laboratory, which was
c.>tablishcd under the leadership of Lawrence
I Icndcrson in 1927 (Chapman and Mitchell 1965;
I)ill lY67; Horvath and Horvath 1973). That year,
I Icnclcrson and colleagues first demonstrated that
~*ntlurancc exercise training improved the efficiency
()I the cardiovascular system by increasing stroke
~~~)lutnc and decreasing heart rate at rest. Two years
I;itcr, Schneider and Ring (1929) published the
rc5ults of a 12-week endurance training program on
c)lle person, demonstratinga 24-percent increase in
"crest load of oxygen" (maximal oxygen uptake).
over the next 15 years, a limited number of exercise
training studies were published that-evaluated the
--+csponsc of maximal oxygen uptake or endurance
Vrformancc capacity to exercise training. These
I~l~luded noteworthy reports by Gemmill and col-
Ic%ues (I931), Robinson and Harmon (1941), and
Knehr. Dill, and Neufeld (1942) on endurance
lraining responses by male college students. HOW-
cVer. none of those early studies compared the

Historical Background, Terminology, Evolution of Recommendations, and Measurement

effects of different types, intensities, durations, or
frequencies of exercise on performance capacity or
health-related outcomes.

Activities surrounding World War II greatly in-
fluenced the research in exercise physiology, and
several laboratories, including the Harvard Fatigue
Laboratory, began directing their efforts toward top-
ics of importance to the military. The other national
concern that created much interest among physiolo-
gists was the fear (discussed earlier in this chapter),
that American children were less fit than their Euro-
pean counterparts. Research was directed toward the
concept of fitness in growth and development, ways
to measure fitness, and the various components of
fitness (Berryman 1995). Major advances were also
made in the 1940s and 1950s in developing the
components of physical fitness (Cureton 1947) and
in determining the effects of endurance and strength
training on measures of performance and physi-
ologic function, especially adaptations of the cardio-
vascular and metabolic systems. Also investigated
were the effects ofexercise trainingon health-related
outcomes, such as cholesterol metabolism (Taylor,
Anderson, Keys 1957; Montoye et al. 1959).
Starting in the late 1950s and continuing through
the 197Os, a rapidly increasing number of published
studies evaluated or compared different components
of endurance-oriented exercise training regimens.
For example, Reindell, Roskamm, and Gerschler
(1962) in Germany, Christensen (1960) in Denmark,
and Yakovlev and colleagues (1961) in Russia
compared-and disagreed-about the relative ben-
efits of interval versus continuous exercise train-
ing in increasing cardiac stroke volume and
endurance capacity. Other investigators began to
evaluate the effects of different modes (Sloan and
Keen 1959) and durations (Sinasalo and Juurtola
1957) of endurance-type training on physiologic
and performance measures.

Karvonen and colleagues' (1957) landmark paper
that introduced using "percent maximal heart rate
reserve" to calculate or express exercise training in-
tensity was one of the first studies designed to com-
pare the effects of two different exercise intensities on
cardiorespiratory responses during exercise. Over the
next 20 years, numerous investigators documented
the effects of different exercise training regimens on a
variety of health-related outcomes among healthy

19


Physical Activity and Health

men and women and among persons under medical
care (Bouchard, Shephard, Stephens 1994). Many of
these studies evaluated the effects of endurance or
aerobic exercise training on cardiorespiratory capac-
ity and were initially summarized by Pollock (1973).
The American College of Sports Medicine (ACSM)
(1975, 1978) and the American Heart Association
(AHA) (1975) further refined the results of this re-
search (see the section on "Evolution of Physical
Activity Recommendations," later in this chapter).
Over the past two decades, experts from numer-
ous disciplines have determined that exercise training
substantially enhances physical performance and have
begun to establish the characteristics of the exercise
required to producespecific healthbenefits (Bouchard,
Shephard, Stephens 1994). Also, behavioral scientists
have begun to evaluate what determines physical
activity habits among different segments of the popu-
lation and are developing strategies to increase physi-
calactivityamongsedentary persons (Dishman 1988).
The results of much of this research are cited in the
other chapters of this report and were the focus of the
various conferences, reports, and guidelines summa-
rized later in this chapter.

  As the literature of exercise science has matured
and recommendations have evolved, certain widely
agreed-on terms have emerged. Because a number of
these occur throughout the rest of this chapter and
report, they are presented and briefly defined in the
following section.

Terminology of Physical Activity,
Physical Fitness, and Health

This section discusses four broad terms used frequently
in this report: physical activity, exercise (or exercise
training), physical fitness, and health. Also included is
a glossary (Table 2-l) of more specific terms and
concepts crucial to understanding the material pre-
sented in later parts of this chapter and report.

Physical activity. Physical activity is defined as
bodily movement produced by the contraction of
skeletal muscle that increases energy expenditure
above the basal level. Physical activity can be cat-
egorized in various ways, including type, intensity,
and purpose.

Because muscle contraction has both mechani-
cal and metabolic properties, it can be classified by

either property. This situation has caused some
confusion. Typically, mechanical classification
stresses whether the muscle contraction produces
movement of the limb: isometric (same length) or
static exercise if there is no movement of the limb, or
isotonic (same tension) or dynamic exercise if there
is movement of the limb. Metabolic classification
involves the availability of oxygen for the contrac-
tion process and includes aerobic (oxygen available)
or anaerobic (oxygen unavailable) processes.
Whether an activity is aerobic or anaerobic depends
primarily on its intensity. Most'activities involve
both static and dynamic contractions and aerobic
and anaerobic metabolism. Thus, activities tend to
be classified according to their dominant features.
The physical activity of a person or group is
frequently categorized by the context in which it
occurs. Common categories include occupational,
household, leisure time, or transportation. Leisure-
time activity can be further subdivided into catego-
ries such as competitive sports, recreational activities
(e.g., hiking, cycling), and exercise training.
Exercise (or exercise training). Exercise and
physical activity have been used synonymously in
the past, but more recently, exercise has been used to
denote a subcategory of physical activity: "physical
activity that is planned, structured, repetitive, and
purposive in the sense that improvement or mainte-
nance of one or more components of physical fitness
is the objective" (Caspersen, Powell, Christensen
1985). Exercise training also has denoted physical
activity performed for the sole purpose of enhancing
physical fitness.

Physical fitness. Physical fitness has been de-
fined in many ways (Park 1989). A generally ac-
cepted approach is to define physical fitness as the
ability to carry out daily tasks with vigor and alert-
ness, without undue fatigue, and with ample energy
to enjoy leisure-time pursuits and to meet unfore-
seen emergencies. Physical fitness thus includes car-
diorespiratory endurance, skeletal muscular
endurance, skeletal muscular strength, skeletal mus-
cular power, speed, flexibility, agility, balance, reac-
tion time, and body composition. Because these
attributes differ in their importance to athletic
performance versus health, a distinction has been
made between performance-related fitness and
health-related fitness (Pate 1983; Caspersen, Powell,
Christensen 1985). Health-related fitness has been

20


Historical Background, Terminology, Evolution of Recommendations, and Measurement

Table 2-1.  Glossary of terms
   ~~__

Aerobic training-Training that improves the efficiency of the
,It,r,)ljic energy-producing systems and that can improve
c ,Ir(tlorespiratory endurance.'

Agility-A skill-related component of physical fitness that relates
i,, the ,~bility to rapidly change the position of the entire body in
,ptlcc~ with speed and accuracy.+
Anaerobic training-Training that improves the efficiency of the
.,n,lerohic energy-producing systems and that can increase
n1u\cular strength and tolerance for acid-base imbalances during
hI&-Intensity effort.'

Balance-A skill-related component of physical fitness that
rctl,ltes to the maintenance of equilibrium while stationary or
mch~ln~.'

Body composition-A health-related component of physical
tltnclss that relates to the relative amounts of muscle, fat, bone,
,I~[I other vital parts of the body.+
Calorimetry-Methods used to calculate the rate and quantity
01 cbnk>rgy expenditure when the body is at rest and during
~.\orci~(~.'

Direct calorimetry-A method that gauges the body's rate
.1n(1 qu.mtity of energy production by direct measurement of
tl1(3 I~otly's heat production; the method uses a calorimeter,
\vhic:h is a chamber that measures the heat expended by the
I1ody.'

tndircct calorimetry-A method of estimating energy
c*spc,nditure by measuring respiratory gases. Given that the
.~rnount of 0, and CO1 exchanged in the lungs normally
(YI~,IIS that used and released by body tissues, caloric
c.upc.nditure can be measured by CO, production and O2
( onsumption..

Grdiorespiratory endurance (cardiorespiratory fitness)-A
tlcb.llth-related component of physical fitness that relates to the
.il~lllty oithe circulatory and respiratory systems to supply oxygen
tlurlng sustained physical activity.+
Coordination-A skill-related component of physical fitness that
rcSl.ltcs to the ability to use the senses, such as sight and hearing,
t~I<~~tl~cr with body parts in performing motor tasks smoothly
.Iml .tccurately.+

Detraining-Changes the body undergoes in response to a
rc.duc.tion or cessation of regular physical training.'
Endurance training/endurance activities-Repetitive, aerobic
art' of large muscles (e.g., walking, bicycling, swimming).*
Exercise (exercise training)-Planned, structured, and repetitive
I)(J(lily movement done to improve or maintain one or more
I omponents of physical fitness.

Flexibility-A health-related component of physical fitness that
rc'l~~tes to the range of motion available at a joint.*
Kilocalorie &cab--A measurement of energy. I kilocalorie = 1
(:dhie = 4,184 joules = 4.184 kilojoules.

Kilojoule (kjoule)-A measurement of energy. 4.184 kilojoules =
4,184 joules = 1 Calorie = 1 kilocalorie.
Maximal heart rate reserve-The difference between maximum
heart rate and resting heart rate.'
Maximal oxygen uptake (i/O, max )-The maximal capacity
for oxygen consumption by the body during maximal exertion.
It is also known as aerobic power, maximal oxygen consumption,
and cardiorespiratory endurance capacity.'
Maximal heart rate (HR max)-The highest heart rate value
attainable during an all-out effort to the point of exhaustion.'
Metabolic equivalent (MET)-A unit used to estimate the
metabolic cost (oxygen consumption) of physical activity. One
MET equals the resting metabolic rate of approximately 3.5 ml
0, o kg-l o min-I .*

Muscle fiber-An individual muscle cell.*

Muscular endurance-The ability of the muscle to continue to
perform without fatigue.'

Overtraining-The attempt to do more work than can be
physically tolerated.*

Physical activity-Bodily movement that is produced by the
contraction of skeletal muscle and that substantially increases
energy expenditure.

Physical fitness-A set of attributes that people have or achieve
that relates to the ability to perform physical activity.
Power-A skill-related component of physical fitness that relates
to the rate at which one can perform work.
Relative perceived exertion (RPE)-A person's subjective
assessment of how hard he or she is working. The Borg scale is a
numerical scale for rating perceived exertion.*
Reaction time-A skill-related component of physical fitness that
relates to the time elapsed between stimulation and the beginning
of the reaction to it.+

Resistance training-Training designed to increase strength,
power, and muscle endurance.*

Resting heart rate-The heart rate at rest, averaging 60 to 80
beats per minute.'

Retraining-Recovery of conditioning after a period of inactivity.*
Speed-A skill-related component of physical fitness that relates
to the ability to perform a movement within a short period of
time.+

Strength-The ability of the muscle to exert force.'
Training heart rate (THR)-A heart rate goal established by using
the heart rate equivalent to a selected training level (percentage
of $0, max ). For example, if a training level of 75 percent i/O,
max is desired, theGO, at 75 percent is determined and the heart
rate corresponding to this V02 is selected as the THR.'

`i rrJn' tVllm()re IH, Costill DL. Physiology ofsport and exercise. Champaign, IL: Human Kinetics. 1994.
' T'lnJ (:()rhin CB. Lindsey R. Concepts in physica/ education with /aboratories. 8th eci. Dubuque, IA: Times Mirror Higher Education Group, 1994.
' "l.!lltt'ci tr(jnl Corhin CB, Lindsey R, 1994, and Wilmore JH, Costill DL, 1994.


Physical Activity and Health

said to include cardiorespiratory fitness, muscular
strength and endurance, body composition, and flex-
ibility. The relative importance of any one attribute
depends on the particular performance or health goal.
  Health. The 1988 International Consensus Con-
ference on Physical Activity, Physical Fitness, and
Health (Bouchard et al. 1990) defined health as "a
human condition with physical, social, and psycho-
logical dimensions, each characterized on a con-
tinuum with positive and negative poles. Positive
health is associated with a capacity to enjoy life and
to withstand challenges; it is not merely the absence
of disease. Negative health is associated with mor-
bidity and, in the extreme, with premature mortal-
ity." Thus, when considering the role of physical
activity in promoting health, one must acknowledge
the importance of psychological well-being, as well
as physical health.

Evolution of Physical Activity
Recommendations

In the middle of the 20th century, recommendations
for physical activity to achieve fitness and health
benefits were based on systematic comparisons of
effects from different profiles of exercise training
(Cureton 1947; Karvonen, Kentala. Mustala 1957;
Christensen 1960; Yakolav et al. 1961; Reindell,
Roskamm, Gerschler 1962). In the 1960s and 1970s,
expert panels and committees, operating under the
auspices of health- or fitness-oriented organizations,
began to recommend specific physical activity pro-
grams or exercise prescriptions for improving physi-
cal performance capacity or health (President's
Council on Physical Fitness 1965; AHA 1972,1975;
ACSM 1975). These recommendations were based
on substantial clinical experience and on scientific
data available at that time.

Pollock's 1973 review of what type of exercise
was needed to improve aerobic power and body
composition subsequently formed the basis for a
1978 position statement by the ACSM titled "The
Recommended Quantity and Quality of Exercise for
Developing and Maintaining Fitness in Healthy
Adults." This statement outlined the exercise that
healthy adults would need to develop and maintain
cardiorespiratory fitness and healthy body composi-
tion. These guidelines recommended a frequency of

exercise training of 3-5 days per week, an intensity
of training of 60-90 percent of maximal heart rate
(equivalent to 50-85 percent of maximal oxygen
uptake or heart rate reserve), a duration of 15-60
minutes per training session, and the rhythmical and
aerobic use of large muscle groups through such
activities as running or jogging, walking or hiking,
swimming, skating, bicycling, rowing, cross-country
skiing, rope skipping, and various endurance games
or sports (Table 2-2).

Between 1978 and 1990, most exercise recom-
mendations made to the general public were based
on this 1978 position statement, even though it
addressed only cardiorespiratory fitness and body
composition. By providing clear recommendations,
these guidelines proved invaluable for promoting
cardiorespiratory endurance, although many people
overinterpreted them as guidelines for promoting
overall health. Over time, interest developed in po-
tential health benefits of more moderate forms of
physical activity, and attention began to shift to
alternativephysicalactivityregimens (HaskelllQ84;
Blair, Kohl, Gordon 1992; Blair 1993).
In 1990, the ACSM updated its 1978 position
statement by adding the development of muscular
strength and endurance as a major objective (ACSM
1990). The recommended frequency, intensity, and
mode of exercise remained similar, but the duration
was slightly increased from 15-60 minutes to 20-60
minutes per session, and moderate-intensity resis-
tance training (one set of 8-12 repetitions of 8-10
different exercises at least 2 times per week) was
suggested to develop and maintain muscular strength
and endurance (Table 2-2). These 1990 recommen-
dations also recognized that activities of moderate
intensity may have health benefits independent of
cardiorespiratory fitness:

Since the original position statement was pub-
fished in 1978, an important distinction has
been made between physical activity as it
relates to health versus fitness. It has been
pointed out that the quantity and quality of
exercise needed to obtain health-related ben-
efits may differ from what is recommended
forfitness benefits. It is now clear that lower
levels ofphysical activity than recommended
by this position statement may reduce the
riskfor certain chronic degenerative diseases


Historical Background, Terminology, Evolution of Recommendations, and Measurement

attd yet may not be of sufficient quantity or
cilia/ity to improve [maximal oxygen uptake].
~\CSM recognizes the potential health benefits
c,fr.cg[41ar exercise performed morefrequently
cl,~d,f~t- longer duration, but at lower intensi-
tics t/Ian prescribed in this position statement.

ln conjunction with a program to certify exercise
professionals at various levels of experience and
~c~Inpetence, the ACSM has published five editions
(,f G&clines for Exercise Testing and Prescription
(ACSM 1975, 1980, 1986, 1991, 1995b) that de-
scribe the components of the exercise prescription
arid explain how to initiate and complete a proper
cscrcise training program (Table 2-2). The ACSM
1~1s also published recommendations on the role
ofcxcrcise for preventing and managing hyperten-
5ion (1993) and for patients with coronary heart
discasc (1994) and has published a position stand
011 osteoporosis (1995a). For the most part, newer
rccommcndations that focus on specific health
outcomes are consistent with the ACSM's 1978
;lnrl 1990 position statements, but they generally
cspand the range of recommended activities to
include moderate-intensity exercise.
  Bctwccn the 1960s and lQQOs, other U.S. health
;~ncl fitness organizations published recommenda-
tions for physical activity. Because these organiza-
tions used the same scientific data as the ACSM, their
position statements and guidelines are similar. A
IW~I&J example is Healthy People 2000 (USDHHS
IWO), the landmark publication of the U.S. Public
I Icalth Service that lists various health objectives for
the nation. (The objectives for physical activity and
~I~UCSS, as revised in 1995 [USDHHS 19951, are
lucludcd as Appendix A of this chapter.) Other
rccommcndations include specific exercise programs
clc\*clopcd for men and women by the President's
Gjuncil on Physical Fitness (1965) and the YMCA
(%lional Council YMCA 1989). The AHA (1972,
1975, 1992, 1993, 1994, 1995) has pbblished for
lull health professionals and the public a series of
l)lWcal activity recommendations and position state-
Illcnts directed at CHD prevention and cardiac reha-
1Jilitation. In 1992, the AHA published a statement
Identifying physical inactivity as a fourth major risk
factor for CHD, along with smoking, high blood
Pressure. and high blood cholesterol (Fletcher et al.
1'192). The American Association of Cardiovascular

and Pulmonary Rehabilitation has also published
guidelines for using physical activity for cardiac
(199 1, 1995) and pulmonary (1993) rehabilitation.
Some of these recommendations provide substantial
advice to ensure that exercise programs are safe for
people at increased risk for heart disease or for
patients with established disease.
  Between the 1970s and the mid-lQQOs, exercise
training studies conducted on middle-aged and older
persons and on patients with lower functional capac-
ity demonstrated that significant.cardiorespiratory
performance and health-related benefits can be ob-
tained at more moderate levels of activity intensity
than previously realized. In addition, population-
based epidemiologic studies demonstrated dose-
response gradients between physical activity and
health outcomes. As a result of these findings, the
most recent CDC-ACSM guidelines recommend that
all adults perform 30 or more minutes of moderate-
intensity physical activity on most, and preferably
all, days--either in a single session or "accumulated"
in multiple bouts, each lasting at least 8-10 minutes
(Pate et al. 1995). This guideline thus significantly
differs from the earlier ones on three points: it
reduces the minimum starting exercise intensity
from 60 percent of maximal oxygen uptake to 50
percent in healthy adults and to 40 percent in pa-
tients or persons with very low fitness; it increases
the frequency of exercise sessions from 3 days per
week to 5-7 days per week, depending on intensity
and session duration; and it includes the option of
accumulating the minimum of 30 minutes per day in
multiple sessions lasting at least 8-10 minutes (Pate
et al. 1995). This modification in advice acknowl-
edges that people who are sedentary and who do not
enjoy, or are otherwise not able to maintain, a regi-
men of regular, vigorous activity can still derive
substantial benefit from more moderate physical
activity as long as it is done regularly.
  The NIH Consensus Development Conference
Statement on Physical Activity and Cardiovascular
Health identifies physical inactivity as a major pub-
lic health problem in the United States and issues a
call to action to increase physical activity levels
among persons in all population groups. (See Ap-
pendix B for full text of the recommendations.) The
core recommendations, similar to those jointly made
by the CDC and the ACSM (Pate et al. 1995), call for

23


Physical Activity and Health

Table 2-2. Selected physical activity recommendations in the United States (1965-1996)

Source                Objective             Type/mode
                                           General fitness

                                           Endurance
                                 Endurance, strength, flexibility
                                 Endurance, strength, flexibility

PCPF (1965)

AHA Recommendations (1972)

YMCA (1973)

ACSM Guidelines (1975)

Physical fitness
CHD prevention
General health and fitness
Cardiorespiratory fitness

AHA Recommendations (1975)

ACSM Position Statement (1978)

USDHEW-Healthy People (1979)

ACSM Guidelines (1980)

ACSM Guidelines (1986)

USDHHS-Surgeon General's Report
on Nutrition and Health (1988)

USPSTF (1989)

ACSM Position Stand (1990)

ACSM Guidelines (1991)

USHHS/USDA Dietary
Guidelines (1990)

AACVPR (1991)

DHHS-Healthy People 2000 (1991)*

AHA Position Statement (1992)

AHA Standards (1992 and 1995)

AACVPR (1993)

ACSM Position Statement (1993)

Secondary prevention in patients
with heart disease

Cardiorespiratory fitness
and body composition

Disease prevention/
health promotion
Cardiorespiratory fitness

Cardiorespiratory fitness

Weight control

Primary prevention in clinical practice
Cardiorespiratory and muscular
fitness

Cardiorespiratory fitness

Health promotion/disease prevention,
weight maintenance
Cardiac rehabilitation

Disease prevention/health promotion

CVD prevention and rehabilitation
CHD prevention and rehabilitation

Pulmonary rehabilitation

Prevention and treatment
of hypertension

Endurance

Endurance

Endurance

Endurance, strength, flexibility

Endurance, strength, flexibility

Endurance

Not specified, implied endurance
Endurance, strength

Endurance, strength, flexibility

Not specified

Endurance, strength

Endurance, strength, flexibility

Endurance

Endurance, strength

Endurance

Endurance, strength

24


Historical Background, Terminology, Evolution of Recommendations, and Measurement

Intensity
Five levels

70-85% MHR
80% i/O, max
60-90% i/O, max
60-90% HRR

T&85% MHR

Endurance

Frequency

Duration

Resistance training

5 x week

3-7 x week

3 x week

3 x week

Approximately 30 minutes

15-20 minutes

40-45 minutes

20-30 minutes

Selected calisthenics

Not addressed

Not specified
Not specified

34 x week

20-60 minutes

Not addressed

  .
Not addressed

50-85% ifO, max
50435% HRR
60-90% MHR

Moderate/hard

3-5 x week

3 x week

5s85%\;/0, max/HRR
ho-90% MH R
io-05% i/O, max/HRR
oo-`10% MHR

Not specified

3-5 x week

3-5 x week

13 x week

AI least moderate
.50-85%i/O, max
W-85'% HRR
OO-OO'%, MHR
40-11.5'%1 00, max
5 5-OO'X, MHR
KI'E = 12-l 6

Not specified

Not specified

3-5 x week

3-5 x week

Not specified

bcrcise following ACSM
I 1 OtlO) and AHA (1983)
rcbc-ommendations
Light/moderate/vigorous

3-5 x week

3-5 x week

b- 50% i/O2 nlax
jO-60% 90, max
jO-60% HR reserve

3-4 x week

13 x week

()()":I HR reserve         3 x week
-W70"/0 i/O, max        3-5 x week

15-60 minutes

15-30 minutes

15-60 minutes

15-60 minutes

2 20 minutes

Not specified

20-60 minutes

15-60 minutes

Not specified

15-60 minutes

20-30 minutes

30-60 minutes

2 30 minutes

20-30 minutes

20-60 minutes

Not addressed

Not specified

Not specified

Not addressed

Not addressed

1 set, 8-l 2 repetitions
8-l 0 exercises
2 days x week
Not specified

Not addressed

l-3 sets, 12-l 5 repetitions
major muscle groups
2-3 days x week
Not specified

Not addressed

1 set, 1 O-l 5 repetitions
8-l 0 exercises,
2-3 days x week

Not addressed

Not specified

--

25


Physical Activity and Health

Table 2-2. Continued

Source

Obiective

Type/mode

AHA Position             CVD prevention
Statement (1993)             and rehabilitation

ACSM Position Stand (1994)

Secondary prevention in patients
with coronary heart disease

AHA Position Statement (1994)

Cardiac rehabilitation

Physical Activity Guidelines
for Adolescents (1994Y

AACVPR (I 995)

Lifetime health promotion
for adolescents

Cardiac rehabilitation

ACSM Guidelines (1995)

Cardiorespiratory fitness
and muscular fitness

ACSM Position Stand (1995)

Prevention of osteoporosis

AHCPR (1995)

Cardiac rehabilitation

AMA Guidelines for
Adolescent Preventive
Services (GAPS) (1994)

CDC/ACSM (1995)*

Health promotion/
physical fitness

Health promotion

USHHYUSDA Dietary
Guidelines (1995)

NHLBI Consensus Conference
(1996)

USPSTF (1996)

Health promotion/disease
prevention, weight maintenance
CVD prevention for adults and
children and cardiac rehabilitation

Primary prevention
in clinical practice

Moderate intensity
(i.e., brisk walking) integrated
into daily routine

Endurance, strength

Endurance and strength training
of moderate intensity following
other guidelines

Endurance

Endurance, strength

Endurance, strength

Strength, flexibility, coordination,
cardiorespiratory fitness
Endurance, strength

Endurance

Endurance

Endurance

Endurance

Endurance, strength, flexibility

26


Historical Background, Terminology, Evolution of Recommendations, and Measurement

- .~__
Intensity

Endurance

Frequency
Not specified

Duration

Resistance training

Not specified

Not specified

Not addressed

4045% 00, max
JO-85% HRR
55-90% MHR
Not specified

3 x week,
nonconsecutive days

Not specified

Moderate/vigorous

> 50% i/O, max
KPE 12-14

3 x week, vigorous
daily, moderate

3-5 x week

JO-SS%i/O, max/HRR
RPE 12-16

3-5 x week

NOI specified         Not specified

7045% MHR

3 x week

Mo(kratc

2 3 x week

2040 minutes

Not specified

2 20 minutes, vigorous
not specified, moderate

30-45 minutes, 200-300
kcal per session or
1,000-l ,500 kcal per week
12-l 5 minutes initially:
20-30 minutes for
conditioning and
maintaining
Not specified

20-40 minutes

20-30 minutes

Not specified

Not specified

Not addressed

1 set, 1 O-l 5 repetitions,
major muscle groups
2-3 days x week
1 set, 8-l 2 repetitions
8-l 0 exercises
2 days x week

Not specified

Not specified

Not addressed

Moderate/hard

All or most days

L 30 minutes per day
in bouts of at least 8-l 0
minutes

Not specified

Modcrate

All or most days

2 30 minutes per day

Not addressed

iMoclcrate/hard

All or most days

2 30 minutes per day

Not addressed

Most days

30 minutes

Not specified

     .~                                                                           --
`4f't8 :\t)twndix B for listing of objectives.  `See Sallis and Patrick, 1994.  *See Pate et al., 1995.
hIa\ 11) `lssnciations: AACVPR = American Association for Cardiovascular and Pulmonary Rehabilitation; ACSM = American College of sports
\\l.(ilc lw; AHA = American Heart Association; AHCPR = Agency for Health Care Policy and Research; CDC = Centers for Disease Control and
I'r15\~*nrmn: NtjLBI = National Heart, Lung, and Blood Institute; PCPF = President's Council on Physical Fitness; USDA = United States Department
oI ,\<rl! ulture: LJSDHEW = United States Department of Health, Education, and Welfare; USDHHS = United States Department of Health and
t tum.1n Swwces: USPSTF = United States Preventive Services Task Force; YMCA = Young Men's Christian Association.
il.\ 111 ,~hhrevialions: CHD = coronary heart disease; CVD = cardiovascular disease; HRR = heart rate reserve; MHR = maximal heart fate;
K"f = r,ltinR oi perceived exertion;i/O> max = maximal oxygen uptake.
\I" ,I(itlre\sed = not included in recommendations. Not specified = recommended but not quantified.

27


Physical Activity and Health

all children and adults to accumulate at least 30
minutes per day of moderate-intensity physical
activity. The recommendations also acknowledge
that persons already achieving this minimum could
experience greater benefits by increasing either the
duration or the intensity of activity. In addition, the
statement recommends more widespread use of car-
diac rehabilitation programs that include physical
activity.

The consensus statement from the 1993 Inter-
national Consensus Conference on Physical Activ-
ity Guidelines for Adolescents (Sallis and Patrick
1994) emphasizes that adolescents should be physi-
cally active every day as part of general lifestyle
activities and that they should engage in 3 or more
20-minute sessions of moderate to vigorous exer-
cise each week. The American Academy of Pediat-
rics has issued several statements encouraging active
play in preschool children, assessment of children's
activity levels, and evaluation of physical fitness
(1992, 1994). Both the consensus statement and
the American Academy of Pediatrics' statements
emphasize active play, parental involvement, and
generally active lifestyles rather than specific vigor-
ous exercise training. They also acknowledge the
need for appropriate school physical education
curricula.

Recognizing the important interrelationship of
nutrition and physical activity in achieving a balance
between energy consumed and energy expended, the
1988 Surgeon General's Report on Nutrition and
Health (USDHHS 1988) recommended physical ac-
tivities such as walking, jogging, and bicycling for at
least 20 minutes, 3 times per week. The 1995 Dietary
Guidclincs Jot- Americans greatly expanded physical
activity guidance to maintain and improve weight.
The bulletin recommends that all Americans engage
in 30 minutes of moderate-intensity physical activity
on all, or most, days of the week (USDA/USDHHS
1995).

The U.S. Preventive Services Task Force
(USPSTF) has recommended that health care pro-
viders counsel all patients on the importance of
incorporating physical activities into their daily
routines to prevent coronary heart disease, hyper-
tension, obesity, and diabetes (Harris et al. 1989;
USPSTF 1989, 1996). Similarly, the American

Medical Association's Guidelines for Adolescent
Preventive Services (GAPS) (AMA 1994) recom-
mends that physicians provide annual physical ac-
tivity counseling to all adolescents.

Summary of Recent Physical
Activity Recommendations
Sedentary persons can increase their physical activ-
ity in many ways. The traditional, structured ap-
proach originally described by the ACSM and others
involved rather specific recommendations regard-
ing type, frequency, intensity, and duration of ac-
tivity. Recommended activities typically included
fast walking, running, cycling, swimming, or aero-
bics classes. More recently, physical activity recom-
mendations have adopted a lifestyle approach to
increasing activity (Pate et al. 1995). This method
involves common activities, such as brisk walking,
climbing stairs (rather than taking the elevator),
doing more house and yard work, and engaging in
active recreational pursuits. Recent physical activity
recommendations thus acknowledge both the struc-
tured and lifestyle approaches to increasing physical
activity. Either approach can be beneficial for a
sedentary person, and individual interests and op-
portunities should determine which is used. The
most recent recommendations cited agree on sev-
eral points:

. All people over the age of 2 years should
accumulate at least 30 minutes of endurance-
type physical activity, of at least moderate
intensity, on most-preferably all-days of
the week.

. Additional health and functional benefits of
physical activity can be achieved by adding
more time in moderate-intensity activity, or
by substituting more vigorous activity.

. Persons with symptomatic CVD, diabetes, or
other chronic health problems who would like
to increase their physical activity should be
evaluated by a physician and provided an
exercise program appropriate for their clinical
  status.


Historical Background, Terminology, Evolution of Recommendations, and Measurement

. Previously inactive men over age 40, women
over age 50, and people at high risk for CVD
should first consult a physician before em-
barking on a program of vigorous physical
activity to which they are unaccustomed.

. Strength-developing activities (resistance train-
ing) should be performed at least twice per
week. At least 8-10 strength-developing exer-
cises that use the major muscle groups of the
legs. trunk, arms, and shoulders should be
performed at each session, with one or two sets
of 8-12 repetitions of each exercise.

Measurement of Physical Activity,
Fitness, and Intensity
~I-hc :lbitity to relate physical activity to health de-
pcnds on accurate, precise, and reproducible mea-
4~~~~~ (\Vilson et al. 1986; National Center for Health
\r;llistics 1989). Measurement techniques have
cvotvc`cl considerably over the years (Park 1989),
c.rcating a shifting pattern of strength and weakness
in I hc cvidcnce supporting the assertion that physi-
(.;I1 ;lctivity improves health (Ainsworth et al. 1994).
I'hc complexity is heightened by the different health
Implications of measuring activity, gauging inten-
YII~. ;~ntl assessing fitness. The tools currently in use
( I`;lt>lc 2-3) must be evaluated not only for their
~~lt'icacy in measuring an individual's status, but also
Ior 1 heir applicability as instruments in larger-scale
L*piclcmiologic research. These tools vary consider-
.llJI!. in the age groups to which they can be applied,
:\4 well as in their cost, in their likelihood of affecting
1 hc behavior they try to measure, and in their accept-
.\hiliry. For example, many of the tools that are
.ll>propriate for young and middle-aged persons are
1~~s so for the elderly and may have no relevance at
.kIt for children. A brief review of these approaches
Ilr(j\.idcs some insight into the current. constellation
of strengths and weaknesses on which epidemio-
I(jgic conclusions rest.

Measuring Physical Activity
Measures Based on Self-Report
l'h!sical activity is a complex set of behaviors most
c(`mmonly assessed in epidemiologic studies by ask-
In3 People to classify their level of physical activity

(LaPorte, Montoye, Caspersen 1985; Caspersen
1989). Techniques used to gather this self-reported
information include diaries, logs, recall surveys,
retrospective quantitative histories, and global self-
reports (Kannel, Wilson, Blair 1985; Wilson et al.
1986; Powell et al. 1987; Caspersen 1989). Surveys
are practical for assessing physical activity in large
populations because they are not costly, are rela-
tively easy to administer, and are generally accept-
able to study participants (Montoye andTaylor 1984;
LaPorte, Montoye, Caspersen 1985.; Caspersen 1989).
Information obtained from self-report instruments
has often been converted into estimates of energy
expenditure (i.e., kilocalories or kilojoules; meta-
bolic equivalents [METS]) or some other summary
measure that can be used to categorize or rank
persons by their physical activity level. This tech-
nique has also been used to convert job classifica-
tions into summary measures.
Diaries can detail virtually all physical activity
performed during a specified (usually short) period.
A summary index can be derived from a diary by
1) summing the total duration of time spent in a
given activity multiplied by an estimated rate of
energy expenditure for that activity, or 2) listing
accumulated time across all activities or time ac-
crued within specific classes of activities. Compari-
sons with indirect calorimetry or with caloric intake
have shown that diaries are accurate indices of daily
energy expenditure (Acheson et al. 1980). Because
diaries are commonly limited to spans of l-3 days,
they may not represent long-term physical activity
patterns (LaPorte, Montoye, Caspersen 1985). Dia-
ries require intensive effort by the participant, and
their use may itself produce changes in the physical
activities the participant does during the monitoring
period (LaPorte, Montoye, Caspersen 1985;
Caspersen 1989).

Logs are similar to diaries but provide a record of
participation in specific types of physical activity
rather than in all activites (King et al. 1991). The
time that activity was started and stopped may be
recorded, either soon after participation or at the end
of the day. Logs can be useful for recording parrici-
pation in an exercise training program. But as with
diaries, they can be inconvenient for the participant,
and their use may itself influence the participant's
behavior.


Physical Activity and Health

Table 2-3. Assessment procedures and their potential use in epidemiologic research

                   Use in           Low    Low
              large  Low Low subject subject Likely to  Accep-  Socially
Measurement   Applicable   scale $    time time   effort  influence table to accep-  Activity
tool          age groups   studies cost  cost cost    cost   behavior persons table  specific

Surveying
Task specific diary
Recall questionnaire
Quantitative history
Global self-report
Monitoring

Behavioral
observation

Job classification

Heart rate monitor

Heart rate and
motion sensor

Electronic motion

sensor

Pedometer

Gait assessment

Accelerometers

Horizontal time
monitor

Stabilometers

Direct calorimetry
indirect calorimetry
Doubly labeled

adult, elderly
adult, elderly
adult, elderly
adult, elderly

adult, elderly

adult

all

all           no

adult, elderly   yes

adult, elderly

child, adult,
elderly

all

child, adult,
elderly

infant

all

adult, elderly

child, adult,

no

yes

no

yes

no

water         elderly  -
Modified from LaPorte, Montoye, Caspersen. Public Health Reports, 1985.
Note that most tests that are applicable for adults can be used in adolescents as well. Few tests can be applied to the pediatric age groups;
among infants, only direct calorimetry, accelerometers, heart rate monitoring, and stabilometers can be used with accuracy.

yes

no

no


no


no

yes

no

yes

no

no


no

yes

no

yes

no

no


no


no


no

yes

yes

no

yes

no

yes

no

no

yes

yes

yes

yes

yes

yes

no


no


no

no


yes

no


yes

no

yes

yes

yes

yes

yes

yes

yes

yes

yes

no


no

yes

no

yes

no

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

no


no


yes

yes

no


no


no

yes

no


no

no


no

no


no

no


no

110

yes

yes

no

?

yes

yes

k-5

?

yes

yes

yes

yes

yes

yes

yes

yes

yes

no


no


yes

?

yes

yes

yes

yes

yes

yes

yes

yes

yes

no


no


ye=

yes

yes

yes

no

yes

yes

no

no


no

no


no

no


no

no

yes

yes

no

Recall surveys are less likely toinfluence behav-
ior and generally require less effort by the respon-
dent than either diaries or logs, although some
participants have trouble remembering details of
past participation in physical activity (Baranowski
1985). Recall surveys of physical activity generally
have been used for time frames of from 1 week to a
lifetime (Kriska et al. 1988; Blair et al. 1991). They
can ascertain either precise details about physical

activity or more general estimates of usual or typical
participation. The recall survey is the method used
for the national and state-based information systems
providing data for Chapter 5 of this report.

The retrospective quantitative history-the most
comprehensive form of physical activity recall survey
-generally requires specific detail for time frames of
up to 1 year (LaPorte, Montoye, Caspersen 1985). If
the time frame is long enough, the quantitative history

30


Historical Background, Terminology, Evolution of Recommendations, and Measurement

can adequately represent year-round physical activ-
ity, For example, the Minnesota Leisure-Time Physi-
cal ,Activity Questionnaire and the Tecumseh
questionnaire obtained information on the average
[rcquency and duration of participation for a specific
list of physical activities performed over the previous
!.ci~r (Montoye and Taylor 1984; Taylor et al. 1978).
rufortunately, obtaining this abundance of data is a
hc:l\y demand on the respondent's memory, and the
complexity of the survey generates additional ex-
pcnsc (LaPorte, Montoye, Caspersen 1985).
Ghbal selJ-reports, another type of recall survey,
ask individuals to rate their physical activity rela-
live to other people's in general or to that of a
similar age and sex group. This easy-to-use ap-
proach, which was employed for the National Health
lntcrvicw Survey (NCHS, Bloom 1982>, tends to
hcst rcprcsent participation in vigorous physical
.lctivity (Washburn, Adams, Haile 1987; Caspersen
;~nd Pollard 1988; Jacobs et al. 1993). A weakness of
rhis approach is that persons reporting the same
rating may have different actual physical activity
prl~filcs (Washburn, Adams, Haile 1987; Caspersen
;lnd Pollard 1988).

Although survey approaches generally apply to
~lults, adolescents, and the elderly, survey instru-
111cnts must often be tailored to the specific demo-
graphic requirements of the group under study.
Rcccnlly, some researchers have suggested develop-
ing special survey instruments for older persons
(Voorrips et al. 1991; Dipietro et al. 1993; Washburn
1-l al. 1993) and adolescents or children (Noland et
ill. 1990; Sallis et al. 1993).

Measures Based on Direct Monitoring
fhc major alternative to surveys is to directly mea-
`urc physical activity through behavioral observa-
[Ion, mechanical or electronic devices, or
physiologic measurements (Table 2-3). Such ap-
IJroaches eliminate the problems of poor memory
.Ind biased self-reporting but are themselves lim-
ltcd by high cost and the burden on participants
~lnd staff. Consequently, these measures have been
used primarily in small-scale studies, though they
Ila\`e been used recently in some large-scale studies
' Lakka, Nyyssonen, Salonen 1994).

Behavioral observation is the straightforward
Uccss of watching and recording what a person
tl"es. Using general guidelines for caloric expenditure

associated with specific activities, a summary estimate
of caloric output can be obtained from such observa-
tion. An important subtype of this approach is the
classification ofwork based on the amount of physical
activity it requires. These approaches can be labor-
intensive (hence prohibitively expensive for large-
scale studies) but are usually well accepted by study
participants.'

In the category of mechanical or electronic mea-
surement, various instruments have been used to
monitor heart rate and thus @o.vide a continuous
recording of a physiologic process that reflects both
the duration and intensity of physical activity. Heart
rate is typically used to estimate daily energy expen-
diture (i.e., oxygen uptake) on physical activity; the
underlying assumption is that a linear relationship
exists between heart rate and oxygen uptake. A
major disadvantage of heart rate monitoring is the
need to calibrate the heart rate-energy expenditure
curve for each individual. Another limitation is that
the relationship between heart rate and energy ex-
penditure is variable for low-intensity physical ac-
tivities. Most monitors have to be worn for extended
periods by the participant, and they pose some dis-
comfort and inconvenience.

Other approaches for using heart rate to measure
physical activity include using the percentage of time
spent during daily activities in various ranges of
heart rate (Gilliam et al. 1981), using the difference
between mean daily heart rate and resting heart rate
(Sallis et al. 1990), and using the integration of the
area under a heart rate versus time curve adjusted for
resting heart rate (Freedson 1989). Heart rate alone
may not be a suitable surrogate for determining the
level of physical activity, given that other factors,
such as psychological stress or changes in body
temperature, can significantly influence heart rate
throughout the day.

A variety of sensors have been developed to
measure physical activity by detecting motion. Pe-
dometers, perhaps the earliest motion sensors, were
designed to count steps and thus measure the dis-
tance walked or run. However, not all pedometers
are reliable enough for estimating physical activity in
either laboratory or field research (Kashiwazaki et al.
1986; Washburn, Janney, Fenster 1990). Electronic
motion sensors tend to perform better than their
mechanical counterparts (Wong et al. 1981; Taylor
et al. 1982; LaPorte et al. 1983). Their output has

31


Physical Activity and Health

been significantly correlated with energy expendi-
ture assessed with indirect calorimetry in controlled
laboratory conditions using graded treadmill exer-
cise (Balogun, Amusa, Onyewadume 1988; Haskell
et al. 1993; Montoye et al. 1996), under short-term
controlled activity (e.g., walking or cycling over a
measured course) for heart rate during laboratory
and daily activities, and for observed behavior in a
controlled setting (Klesges and Klesges 1987; Rogers
et al. 1987; Freedson 1989; Sallis et al. 1990;
Washburn, Janney, Fenster 1990). Direct validation
has shown reasonable correlation with physical ac-
tivity records completed over a year (Richardson et
al. 1995). Recording simultaneously both the heart
rate and the motion from sensors on several parts of
the body and then calibrating each individual's heart
rate and motion sensor output versus oxygen uptake
for various activities can accurately estimate the
energy expended from physical activity (Haskell et
al. 1993). Several other devices (e.g., accelerometers,
stabilometers) are of lesser value for large-scale stud-
ies, and their use is limited to small physiologic
investigations.

Methods for physiologically monitoring energy
expenditure include direct calorimetry (requiring the
participant to remain in a metabolic chamber) and
indirect calorimetry (requiring the participant to wear
a mask and to carry equipment for analyzing expired
air). Both methods are too expensive and complicated
for use in large-scale studies. Another physiologic
measurement, the use of doubly labeled water, offers
researchers special opportunities to assess energy ex-
penditure. By using two stable isotopes (?H?O and
H,`"O) measured every few days or weeks in the urine,
researchers can calculate the rate of carbon dioxide
production-a reflection of the rate ofenergy produc-
tion in humans over time. According to their body
weight, study participants drink a specified amount of
these isotopes. A mass spectrometer is used to track
the amount of unmetabolized isotope in the urine.
Although this technique obtains objective data with
little effort on the part of participants, two disadvan-
tages are its relatively high cost and its inability to
distinguish between typesofactivitiesperformed. The
technique has been proven accurate when compared
withindirect calorimetry (Klein etal. 1984; Westerterp
et al. 1988; Edwards et al. 1990).

Measuring Intensity of Physical Activity
Common terms used to characterize the intensity
of physical activity include light or low, moderate
or mild, hard or vigorous, and very hard or strenu-
ous (Table 2-4). A frequent approach to classify-
ing intensity has been to express it relatively-that
is, in relation to a person's capacity for a specific
type of activity. For example, the intensity pre-
scribed for aerobic exercise training usually is ex-
pressed in relation to the p.erson's measured
cardiorespiratory fitness (ACSM 1990). Because
heart rate during aerobic exercise is highly associ-
ated with the increase in oxygen uptake, the per-
centage of maximal heart rate is often used as a
surrogate for estimating the percentage of maximal
oxygen uptake (ACSM 1990). Exercise intensity
can also be expressed in absolute terms, such as a
specific type of activity with an assigned intensity
(for example, walking at 4 miles per hour or jogging
at 6 miles per hour). Such quanta of work can also
be described in absolute terms as METS, where one
MET is about 3.5 ml 0, o kg-' o min.`, corresponding
to the body at rest. The workloads in the just-
quoted example are equivalent to 4 and 10 METS,
respectively. The number of METS associated with
a wide range of specific activities can be estimated
from aggregated laboratory and field measurements
(Ainsworth, Montoye, Leon 1994).
  The process of aging illustrates an important
relationship between absolute and specific mea-
sures. As people age, their maximal oxygen uptake
decreases. Activity of a given MET value (an abso-
lute intensity) therefore requires a greater percent-
age of their maximal oxygen uptake (a relative
intensity). The aforementioned walk at 4 miles per
hour (4 METS) may be light exercise for a 20-year-
old, moderate for a 60-year-old, and vigorous for an
80-year-old.

Most exercise training studies have used relative
intensity to evaluate specific exercise training regi-
mens. On the other hand, observational studies relat-
ing physical activity to morbidity or mortality usually
report absolute intensity or total amount of physical
activity estimated from composite measures that in-
clude intensity, frequency, and duration. It is thus
difficult to compare the intensity of activity that
improves physiologic markers with the intensity of
activity that may reduce morbidity and mortality.


Historical Background, Terminology, Evolution of Recommendations, and Measurement

Table 2-4. Classification of physical activity intensity, based on physical activity lasting up to 60 minutes
                                            Strength-type
                    Endurance-type activity                   exercise

                          Absolute intensity (METS)         Relative
          Relative intensity         in healthy adults (age in years)      intensity*

                                                              Maximal
     90, max (`7'~)  Maximal                 Middle-        Very         voluntary
       heart rate    heart          Young   aged     Old     old            contraction
Intensity   reserve (%)   rate (%)   RPE+     (20-39)   (40-64)   (65-79)   W+)     RPE     (%)

\ 1'1\' llglll   <25         <30      <9       <3.0     <2.5     <2.0     11.25     <lO   <30


I I:*111       25-44       30-49     9-10      3.0-4.7    2.5-4.4    2.0-3.5    1.26-2.2   10-11    30-49


\\I I( I~Y,lll~    45-59       SO-69     11-12     4.8-7.1    4.5-5.9    3.6-4.7    2.3-2.95   12-13    50-69


) I.110       60-84       70-89     13-16     7.2-10.1   6.0-8.4    4.8-6.7   3.0-4.25   14-16    70-84

\;VV h,lrd   285         290      >16      210.2     28.5      26.8      24.25      17-19   >85

\\.,\llll.ll'    100         100      20       12.0      10.0     8.0      5.0      20      100
                ~-

1,)(~1~~ .' .& Imlvided courtesy of Haskell and Pollock.
`I:.I..,Y~ on 11 -1 2 repetitions for persons under age 50 years and 1 O-l 5 repetitions for persons aged 50 years and older.
*I:SIII: I.III~): oi Relative Perceived Exertion 6-20 scale (Borg 1982).
"X\.I\IIII.I~ V.IIUVS are mean values achieved during maximal exercise by healthy adults. Absolute intensity (METS) values are approximate mean
\.IIIIC+ lor ~NV. Mean values for women are approximately l-2 METS lower than those for men.

Rcccnt public health guidelines and research
rclwrts have used absolute intensity to define ap-
I)ropriatc levels of physical activity, but the term
~~;~b~,olutc" may convey a misplaced sense of preci-
GOII. For example, the CDC-ACSM guidelines (Pate
1.1 ;II. 1~5) use absolute intensity to classify brisk
\\~;tlking as moderate physical activity. In contrast,
I I~~cclllty People 2000 objective 1.3 defines brisk
\valking as "light to moderate" intensity and takes
~rlto ilccount the age- and sex-related variability in
maximal capacity (USDHHS 1990). One solution to
rhih inconsistency in terminology is to create con-
\i.ctcnt categories that equate a variety of measures
lo the same adjective (Table 2-4). Using such a
rubric, the observations of Spelman and colleagues
( 1993) that brisk walking for healthy adults aged
-- ' `-58 years demands 40-60 percent of their aerobic
I'o\\`er suggests a correspondence with 3-5 METS
.lnd a classification of moderate intensity. Those
I)rcscribing an exercise pattern for adults can use
rhc rating of perceived exertion (RPE) scale (ACSM
1 W 1). An RPE of 10-l 1 corresponds to light inten-
`11~~ 12-13 to moderate intensity, and 14-16 to
hard intensity (Table 2-4), and the approximate

physiologic equivalents can be estimated. This type
of subjective scale furnishes a convenient way to
monitor performance.

Measuring Physical Fitness

Perhaps the most highly developed measurement
area is the assessment of physical fitness, since it
rests on physiologic measurements that have good
to excellent accuracy and reliability. The major foci
of fitness measurements are endurance (or cardio-
respiratory fitness), muscular fitness, and body
composition.

Endurance

Cardiorespiratory fitness, also referred to as cardio-
respiratory capacity, aerobic power, or endurance
fitness, is largely determined by habitual physical
activity. However, other factors influence cardio-
respiratory fitness, including age, sex, heredity,
and medical status (Bouchard, Shepard, Stevens
1994).

The best criterion of cardiorespiratory fitness is
maximal oxygen uptake or aerobic power NO, max).
Measured in healthy persons during large muscle,


Physical Activity and Health

dynamic activity (e.g., walking, running, or cycling),
VO, max is primarily limited by the oxygen transport
capacity of the cardiovascular system (Mitchell and
Blomqvist 1971).VO, max is most accurately deter-
mined by measuring expired air composition and
respiratory volume during maximal exertion. This
procedure requires relatively expensive equipment,
highly trained technicians, and time and coopera-
tion from the participant, all of which usually limit
its use in large epidemiologic studies (Montoye et al.
1970; King et al. 1991).

  Because the individual variation in mechanical
and metabolic efficiency is for activities that do not
require much skill-such as walking or running on a
motor-driven treadmill, cycling on a stationary bi-
cycle ergometer, orclimbing steps-oxygen uptake
can be quite accurately estimated from the rate of
work (Siconolfi et al. 1982). Thus,VO? max can be
estimated from the peak exercise workload during a
maximal exercise test without measuring respiratory
gases. Such procedures require an accurately cah-
brated exercise device, careful adherence to a spe-
cific protocol, and good cooperation by the
participant. They have been used in numerous exer-
cise training studies for evaluating the effects of
exercise on cardiovascular risk factors and perfor-
mance, in secondary prevention trials for patients
after hospitalization for myocardial infarction, and
in some large-scale observational studies (Blair et al.
1989; Sidney et al. 1992).

Any maximal test to assess cardiorespiratory
fitness imposes a burden on both the participant
and the examiner. To reduce this burden, several
submaximal exercise testing protocols have been
developed. With these protocols, the heart rate
response to a specified workload is used to predict
theVOL max. The underlying assumption (besides
the linear relationship between heart rate and oxy-
gen uptake) is that the participant's maximal heart
rate can be estimated accurately. Both assumptions
are adequately met when a standardized protocol is
used to test a large sample of healthy adults. In some
cases, no extrapolation to maximal values is per-
formed, and an individual's cardiorespiratory fit-
ness is expressed as the heart rate at a set workload
(e.g., heart rate at 5 kilometers/hour or at 100
watts) or at the workload required to reach a spe-
cific submaximal heart rate (workload at a heart
rate of 120 beats/minute).

In another approach to assessing cardiorespi-
ratory fitness, participants usually walk, jog, or
run a specified time or distance, and their perfor-
mance is converted to an estimate of VO, max
(Cooper 1968). These procedures have been fre-
quently used to test the cardiorespiratory fitness
of children, of young adults, or of groups that have
occupation-related physical fitness requirements,
such as military and emergency service personnel.
In many cases, these tests require maximal or
near-maximal effort by the participant and thus
have not been used for older persons or those at
increased risk for CVD. The advantage is that large
numbers of participants can be tested rapidly at low
cost. However, to obtain an accurate evaluation,
participants must be willing to exert themselves
and know how to set a proper pace.

Muscular fitness

Common measures of muscular fitness are muscular
strength, muscular endurance, flexibility, and bal-
ance, agility, and coordination. Muscular strength
can be measured during performance of either static
or dynamic muscle contraction (NCHS, Wilmore
1989). Because muscular strength is specific to the
muscle group, the testing of one group does not
provide accurate information about the strength of
other muscle groups (Clarke 1973). Thus, for a
comprehensive assessment, strength testing must
involve at least several major muscle groups, includ-
ing the upper body, trunk, and lower body. Standard
tests have included the bench press, leg extension,
and biceps curl using free weights. The heaviest
weight a person can lift only one time through the
full range of motion for a particular muscle group is
considered the person's maximum strength for that
specific muscle group.

Muscular endurance is specific to each muscle
group. Most tests for use in the general population do
not distinguish between muscular endurance and
muscular strength. Tests of muscular endurance and
strength, which include sit-ups, push-ups, bent-arm
hangs, and pull-ups, must be properly administered
and may not discriminate well in some populations
(e.g., pull-ups are not a good test for many popula-
tions because a high percentage of those tested will
have 0 scores). Few laboratory tests of muscular
endurance have been developed, and such tests usu-
ally involve having the participant perform a series of

34


Historical Background, Terminology, Evolution of Recommendations, and Measurement

contractions at a set percentage of maximal strength
and at a constant rate until the person can no longer
continue at that rate. The total work performed or
the test duration is used as a measure of muscular
endurance.

Flexibility is difficult to measure accurately and
reliably. Because it is specific to the joint being
tested, no one measure provides a satisfactory index
of an individual's overall flexibility (Harris 1969).
Field testing of flexibility frequently has been lim-
ited to the sit-and&reach test, which is considered to
be a measure of lower back and hamstring flexibility.
The criterion method for measuring flexibility in the
laboratory is goniometry, which is used to measure
the angle of the joint at both extremes in the range of
motion (NCHS, Wilmore 1989).
  Balance, agility, and coordination are especially
important among older persons, who are more prone
to fall and, as a result, suffer fractures due to reduced
bone mineral density. Field methods for measuring
balance, agility, and coordination have included
various balance stands (e.g., one-foot stand with
eyes open and with eyes closed; standing on a narrow
block) and balance walks on a narrow line or rail
(Tse and Bailey 1992). In the laboratory, computer-
based technology is now being used to evaluate
balance measured on an electronic force platform or
IO analyze a videotape recording of the participant
walking (Lehmann et al. 1990). Agility or coordina-
lion are measured most frequently by using a field
IC`SI, such as an agility walk or run (Cureton 1947).
In the laboratory, coordination or reaction/move-
ment time are determined by using electronic signal-
ing and timing devices (Spirduso 1975). More
dcvclopment is needed to establish norms using
standardized tests for measuring balance, agility,
ilnd coordination, especially of older persons.

Body Composition

In most population-based studies that have provided
Information on the relationship between physical
activity and morbidity or mortality, body composi-
tion has been estimated by measuring body height
and weight and calculating body mass index (weight/
height?). The preferred method for determining
;unount of body fat and lean body mass in exercise
[raining studies has been hydrostatic or underwater
\vcighing (NCHS, Wilmore 1989); however, this

method lacks accuracy in some populations, includ-
ing older persons and children (Lohman 1986).
Anthropometric measurements (i.e., girths, diam-
eters, and skinfolds) used to calculate the percentage
of body fat have varying degrees of accuracy and
reliability (Wilmore and Behnke 1970).
Data now suggest that the distribution of body
fat, especially accumulation in the abdominal area,
and total body fat are significant risk factors for CVD
and diabetes (Bierman and Brunzell 1992; Blumberg

and Alexander 1992). Researchers have determined
the magnitude of this abdominal or central obesity
by calculating the waist-to-hip circumference ratio
or by using new electronic methods that can image
regional fat tissue. New technologies that measure
body composition include total body electrical con-
ductivity (Segal et al. 1985), bioelectrical impedance
(Lukaski et al. 1986), magnetic resonance imaging
(Lohman 1984), and dual-energy x-ray absorptio-
metry (DEXA) (Mazess et al. 1990). These new
procedures have substantial potential to provide
new information on how changes in physical activity
affect body composition and fat distribution.

Valicfity of Measurements

Health behaviors are difficult to measure, and this is
certainly true for the behavior of physical activity. Of
particular concern is how well self-reported physical
activity accurately represents a person's habitual
activity status. Factors that interfere with obtaining
accurate assessments include incomplete recall, ex-
aggeration of amount of activity, and nonrepresenta-
tive sampling of time intervals during which activity
is assessed.

One of the principal difficulties in establishing the
validity of a physical activity measure is the lack of a
suitable "gold-standard" criterion measure for com-
parison. In the absence of a true criterion measure,
cardiorespiratory fitness has often been used as a
validation standard for physical activity surveys. Al-
though habitual physical activity is a major determi-
nant of cardiorespiratory fitness, other factors, such as
genetic inheritance, also play a role. Therefore, a
perfect correlation between physical activity report-
ing and cardiorespiratory fitness would not be ex-
pected. Nonetheless, correlations of reported physical
activity with measured cardiorespiratory fitness have
been examined. Table 2-5 shows results from studies


Physical Activity and Health

Table 2-5.  Correlation of two survey instruments with physiologic measures of caloric exchange
Study             Sample     Physiologic test          Correlation coefficient

Taylor et al. (1978)

Skinner et al. (1966)

Leon et al. (1981)

DeBacker et al. (1981)

Jacobs et al. (1993)

Richardson et al. (1995)

Albanes et al. (1990)

Montoye et al. (1996)

Siconolfi et al. (1985)

Jacobs et al. (1993)

Albanes et al. (1990)

Montoye et al. (1996)

Minnesota Leisure-Time Physical Activity Questionnaire

    175 men      Treadmill endurance

    54 men      Submaximal treadmill text

    175 men      Treadmill
             Submaximal heart rate

    1,513 men    Submaximal treadmill test

    64 men    i/O, max
    & women     Submaximal heart rate

    78 men    VO, max
    & women

    21 men     Resting caloric intake

    28 men     Doubly labeled water

     College Alumni Study Survey

    36 men    i/O, max
    32 women   i/O, max

    64 men
     & women    00, max
              Submaximal heart rate

    21 men     Resting caloric intake

    28 men     Doubly labeled water
           Energy intake, 7 days

0.45

0.13 NS

0.41
0.59

0.10

0.43
0.45

0.47

0.17 NS

0.26 NS

0.29
0.46

0.52
0.52

0.32 NS

0.39
0.44

NS = nonsignificant correlation coefficient; all others were statistically significant.

in which questionnaire data from the Minnesota
Leisure-Time Physical Activity Questionnaire (Taylor
et al. 1978) and the College Alumni Study survey
(Paffenbarger et al. 1993) are compared with physi-
ological measures, in most cases cardiorespiratory
fitness. Although most correlation coefficients (e.g.,
Pearson's r) are statistically significant, they exhibit
considerable variability (range 0.10 to 0.59), and the
overall central tendency (median,. 0.41) suggests
only moderate external validity. However, in a
study of predictors of cardiorespiratory fitness
among adults (Blair et al. 1989). in all age and sex
subgroups, self-reported physical activity was the
principal contributor to the predictive models that
also included weight, resting heart rate, and current
smoking. Thus, self-reported physical activity may

not be perfectly correlated with cardiorespiratory
fitness, but it may be the predominant predictive
factor.

Because misclassification of physical activity, as
could occur by using an invalid measure, would tend
to bias studies towards finding no association, the
consistently found associations between physical.ac-
tivity and lower risk of several diseases (as is discussed
in Chapter 4) suggest that the measure has at least
some validity. Moreover, they suggest that a more
precise measure of physical activity would likely yield
even stronger associations with health. Thus, although
measurement of physical activity by currently avail-
able methods may be far from ideal, it has provided a
means to investigate and demonstrate important health
benefits of physical activity.

36


Historical Background, Terminology, Evolution of Recommendations, and Measurement

Chapter Summary

The assertion that frequent participation in physical
activity contributes to better health has been a recur-
ring theme in medicine and education throughout
much of Western history. Early empirical observa-
tions and case studies suggesting that a sedentary life
was not healthy have been supported by rigorous
scientific investigation that has evolved over the past
century. In recent decades, a number of experimental
and clinical specialties have contributed substan-
tially to an emerging field that may accurately be
described as exercise science. This field includes
disciplines ranging from exercise physiology and
biomechanics to physical activity epidemiology, ex-
ercise psychology, clinical sports medicine, and pre-
ventive medicine.' Research findings from these
specialties provide the basis for this first Surgeon
General's report on physical activity and health.
Numerous expert panels, committees, and confer-
cnces have been convened over the years to evaluate
the evidence relating physical activity and health.
These gatherings have laid a solid foundation for the
current consensus that for optimal health, people of
all ages should be physically active. on most days.
Specific exercise recommendations have empha-
sized only vigorous activity for cardiorespiratory
fimcss until recently, when the benefits of moderate-
intensity physical activity have been- recognized
ani promoted as well.

Conclusions

1. Physical activity for better health and well-being
has been an important theme throughout much
of western history.

2. Public health recommendations have evolved
from emphasizingvigorousactivity for cardiores-
piratory fitness to including the option of moder-
ate levels of activity for numerous health benefits.

3.

4.









5.









6.

Recommendations from experts agree that for
better health, physical activity should be per-
formed regularly. The most recent recommenda-
tions advise people of all ages to include a
minimum of 30 minutes of physical activity of
moderate intensity (such as brisk walking) on
most, if not all, days of the week. It is also
acknowledged that for most people, greater health
benefits can be obtained by engaging in physical
activity of more vigorous intensity or of longer
duration.

Experts advise previously sedentary people em-
barking on a physical ac&ity program to start
with short durations of moderate-intensity activ-
ity and gradually increase the duration or inten-
sity until the goal is reached.

Experts advise consulting with a physician before
beginning a new physical activity program for
people with chronic diseases, such as CVD and
diabetes mellitus, or for those who are at high risk
for these diseases. Experts also advise men over
age 40 and women over age 50 to consult a
physician before they begin a vigorous activity
program.

Recent recommendations from experts also
suggest that cardiorespiratory endurance ac-
tivity should be supplemented with strength-
developing exercises at least twice per week
for adults, in order to improve musculoskel-
eta1 health, maintain independence in per-
forming the activities of daily life, and reduce
the risk of falling.

37


Physical Activity and Health

Appendix A: Healthy People 2000 Objectives

The nation's public health goals for the 1990s and beyond, as presented in Healthy People2000 (USDHHS 1990),
aim co increase the span of healthy life for all Americans, to reduce health disparities among Americans, and to
achieve access to preventive services for all Americans. Reproduced here are the Healthy People 2000 objectives
for physical activity and fitness as revised in 1995 (USDHHS 1995).

Duplicate objectives that appear in two or more priority areas are marked with an asterisk alongside the
objective number.

Physical Activity and Fitness
Health Status Objectives

1.1*  Reduce coronary heart disease deaths to no more than 100 per 100,000 people.
                 Special Population Target
Coronary Deaths (per IOOJIOO)                     2000 Target
l.la   Blacks                                         115
1.2*  Reduce overweight to a prevalence of no more than 20 percent among people aged 20 and older and
   no more than 15 percent among adolescents aged 12-19.

                 Special Population Target
Overweight Prevalence
1.2a  Low-income women aged 20 and older
1.2b  Black women aged 20 and older
1.2c  Hispanic women aged 20 and older
1.2d  American Indians/Alaska Natives
1.2e  People with disabilities
1.2f  Women with high blood pressure
1.2g  Men with high blood pressure
1.2h Mexican-American men

2000 Target
  25%
  30%
  25%
  30%
  25%
  41%
  35%
  25%

NOW For pcoplc aged 20 and oldcr, ovcrwcight is dcJincd as body mass index (BMI) equal to or grcatcr than 27.8Jor men and 27.3Jor women. For adolescents,
overweight is d&cd us BMI equal to or grrutcr than 23.Ojor males aged 12-14.24.31 or males ugcd 15-I 7, 25.8Jor males aged 18-19, 23.4forfemales aged
12-14.24.8~~Jemulcs aged 15-Z 7, and25.7forjcmuIcs aged 18-19. The values/or adults arc thcgender-speciJic85thpercentilevalues ofthe 1976-80 National
Hculth and Nutrition Examination Survey (NHANES II), ef
                                  r crencc population 20-29 ycurs of age For adolescents, overweight was dejned using BMI cute//S
boscd on modiJicd age- and gcndcr-spcc$c 85th pcrccntile values o/the NHANES II. BMI is calculated by dividing weight in kilograms by the square of height
in mctcrs. The cut points used to dcJinc overweight approximate the 120 percent ojdcsirable body weight dejnition used in the 1990 objectives.

Risk Reduction Objectives

1.3*  Increase to at least 30 percent the proportion of people aged 6 and older who engage regularly, preferably
  daily, in light to moderate physical activity for at least 30 minutes per day.

               Special Population Targets
Moderate Physical Activity                        2000 Target
1.3a  Hispanics aged 18 and older                          25 %
   5 or more times per week

Note: Light to modcr-utc physical activity rcquircs sustuincd, rhythtmc muscular movements. is at least equivalent to sustained walking. and is performed at less
thun 60 pet-cent ojmuximum heart ratejor age. Maximum heart rate equals roughly 220 beats per minute minus age. Examples may include walking, swimming,
cycling, dancing, gar-drning und yurdwork, various domestic and occupational activities, and games and other childhood pursuits.

38


Historical Background, Terminology, Evolution of Recommendations, and Measurement

1.4

Increase to at least 20 percent the proportion of people aged 18 and older and to at least 75 percent the
proportion of children and adolescents aged 6-17 who engage in vigorous physical activity that
promotes the development and maintenance of cardiorespiratory fitness 3 or more days per week for
20 or more minutes per occasion.

                  Special Population Targets
Vigorous Physical Activity
1 .Sa  Lower-income people aged 18 and older
   (annual family income <$20,000)
1.4b  Blacks aged 18 years and older
1.4c  Hispanics aged 18 years and older

2000 Target
  12%


  17%
  17%

Nofc: Vigorous physical activities are rhythmic, rcpetitivc physical activities that USC large muscle groups at 60 percent or more ojmarimum hurt ratcjor ugc.
Art cxcrcisc ruts ~$60 percent oJ maximum heart ratcjor agr is about 50 pcrccnt o~maximal cardiorcspiratory capacity und is suJJicicntfor cardiorcspll-ator:\~
C-omlltiotlitlg. Muximum heart rate equals roughly 220 beats per minute minus age.

1.5  Reduce to,no more than 15 percent the proportion of people aged 6 and older who engage in no leisure-
   time physical activity.

                   Special Population Targets
No Leisure-Time Physical Activity
1.5a  People aged 65 and older
1.5b  People with disabilities
1.5c  Lower-income people (annual family
   income <$20,000)
1.5d  Blacks aged 18 and older
1.5c  Hispanics aged 18 and older
1.5f  American Indians/Alaska Natives aged 18 and older

2000 Target
  22%
  20%
  17%


  20%
  25%
  21%

NOIC For this objcctivc. pcoplc with disabilitirs arc pcoplc who report any limitation in activity due to chronic conditions.

I .6  Increase to at least 40 percent the proportion of people aged 6 and older who regularly perform physical
  activities that enhance and maintain muscular strength, muscular endurance, and flexibility.
I .7"  Increase to at least 50 percent the proportion of overweight people aged 12 and older who have adopted
  sound dietary practices combined with regular physical activity to attain an appropriate body weight.

Moption of Weight-Loss Practices
1.7a  Overweight Hispanic males
   aged 18 and older
1.71,  Overweight Hispanic females
   aged 18 and older

Special Population Targets

2000 Target
  24%


  22%

So-vices and Protection Objectives

I .H  Increase to at least 50 percent the proportion of children and adolescents in lst-12th grade who
   participate in daily school physical education.
1 .c)  Increase to at least 50 percent the proportion of school physical education class time that students spend
  being physically active, preferably engaged in lifetime physical activities.

39


Physical Activity and Health

Note: Lifetimeactivitiesareactivities that may be readily carried intoadulthoodbecnuse they generally need only oneortwopeople. Examples include swimming,
bicycling, jogging, and racquet sports. Also counted as lijetime activities are vigorous social activities such as dancing. Competitive group sports and activities
typically played only by young children such as group games are excluded.

1.10  Increase the proportion of worksites offering employer-sponsored physical activity and fitness
   programs as follows:

Worhsite Size                              2000 Target
50-99 employees                                      20%
loo-249 employees                                     35%
250-749 employees                                    50%
1750 employees                                       80%

1.11  Increase community availability and accessibility of physical activity and fitness facilities as follows:

Facility
Hiking, biking, and fitness trail miles
Public swimming pools
Acres of park and recreation open space

    2000 Target
  1 per 10,000 people
  1 per 25,000 people
  4 per 1,000 people
(250 people per managed acre>

1.12  Increase to at least 50 percent the proportion of primary care providers who routinely assess and counsel
  their patients regarding the frequency, duration, type, and intensity of each patient's physical activity
   practices.

Health Status Objective

1.13*  Reduce to no more than 90 per 1,000 people the proportion of all people aged 65 and older who have
   difficulty in performing two or more personal care activities thereby preserving independence.

Difficulty Performing
Self Care (per 1,000)
1.13a  People aged 85 and older
1.13b Blacks aged 65 and older

Special Population Targets

2000 Target
  325
  98

Note: Personal care activities are bathing. dressing, using the toilet, getting in and out ofbed or chair, and eating

40


Historical Background, Terminology, Evolution of Recommendations, and Measurement

Appendix B: NI H Consensus

Conference Statement
III Press (3/I8/96)
Sational Institutes of Health
Consensus Development Conference Statement
Physical Activity and Cardiovascular Health
Dcccmber 18-20, I995

31~ Consensus Statements are prepared by a
r,nnadvocatc, non-Federal panel ofexperts, based on
( l J presentations by investigators working in areas
rclcvant to the consensus questions during a 2-day
public session; (2) questions and statements from
~.~~llfcrcncc attendees, during open discussion peri-
& that arc part of the public session; and (3) closed
deliberations by the panel during the remainder of
rllr second day and morning qf the third. This
\I;ltcmcnt is an independent report of the panel and
I, Ilot a policy statement of the NIH or the Federal
(;~,vcrnmcnt.

Alxtract

( )/Jjt.c.li\fc*. To provide physicians and the general
I"ll)lic with a responsible assessment of the relation-
\llilJ hctwccn physical activity and cardiovascular
11lx1t11.

f'clrficipmls. A non-Federal, nonadvocate, 13-
~~~c~uhcr panel representing the fields of cardiology,
1)~~~chology, exercise physiology, nutrition, pediat-
rlc'h. public health, andepidemiology. Inaddition, 27
cspcrts in cardiology, psychology, epidemiology,
c*scrcisc physiology, geriatrics, nutrition, pediatrics,
Wlic health, and sports medicine presented data to
[ hc panel and a conference audience of 600.

~~~YICC. The literature was searched through
xlcdlinc and an extensive bibliography of references
\\`;ls provided to the panel and the conference audi-
c~c. Experts prepared abstracts with relevant cita-
[i~)ns from the literature. Scientific evidence was
.W'C~I precedence over clinical anecdot'al experience.

CO~ISCmUS Process. The panel, answering pre-
defined questions, developed their conclusions
hascd on the scientific evidence presented in open
lorl~m and the scientific literature. The panel com-
I'"scd a draft statement that was read in its entirety
bind circulated to the experts and the audience for

comment. Thereafter, the panel resolved conflict-
ing recommendations and released a revised state-
ment at the end of the conference. The panel
finalized the revisions within a few weeks after the
conference.

Conclusions. All Americans should engage in
regular physical activity at a level appropriate to
their capacity, needs, and interest. Children and
adults alike should set a goal of accumulating at
least 30 minutes of moderate-intensity physical
activity on most, and preferably, all days of the
week. Most Americans have little or no physical
activity in their daily lives, and accumulating evi-
dence indicates that physical inactivity is a major
risk factor for cardiovascular disease. However,
moderate levels of physical activity confer signifi-
cant health benefits. Even those who currently
meet these daily standards may derive additional
health and fitness benefits by becoming more physi-
cally active or including more vigorous activity. For
those with known cardiovascular disease, cardiac
rehabilitation programs that combine physical ac-
tivity with reduction in other risk factors should be
more widely used.

Introduction

Over the past 25 years, the United States has experi-
enced a steady decline in the age- adjusted death toll
from cardiovascular disease (CVD), primarily in
mortality caused by coronary heart disease and stroke.
Despite this decline, coronary heart disease remains
the leading cause of death and stroke the third
leading cause of death. Lifestyle improvements by
the American public and better control of the risk
factors for heart disease and stroke have been major
factors in this decline.

Coronary heart disease and stroke have many
causes. Modifiable risk factors include smoking,
high blood pressure, blood lipid levels, obesity, dia-
betes, and physical inac.tivity. In contrast to the
positive national trendsobserved with cigarette smok-
ing, high blood pressure, and high blood cholesterol,
obesity and physical inactivity in the United States
have not improved. Indeed automation and other
technologies have contributed greatly to lessening
physical activity at work and home.

41


Physical Activity and Health

The purpose of this conference was to examine
the accumulating evidence on the role of physical
activity in the prevention and treatment of CVD and
its risk factors.

Physical activity in this statement is defined as
"bodily movement produced by skeletal muscles
that requires energy expenditure" and produces
healthy benefits. Exercise, a type of physical activity,
is defined as "a planned, structured, and repetitive
bodily movement done to improve or maintain one
or more components of physical fitness." Physical
inactivity denotes a level of activity less than that
needed to maintain good health.
Physical inactivity characterizes most Ameri-
cans. Exertion has been systematically engineered
out of most occupations and lifestyles. In 1991, 54
percent of adults reported little orno regular leisure
physical activity. Data from the 1990 Youth Risk
Behavior Survey show that most teenagers in grades
9-12 are not performing regular vigorous activity.
About 50 percent of high school students reported
they are not enrolled in physical education classes.
Physical activity protects against the develop-
ment of CVD and also favorably modifies other CVD
risk factors, including high blood pressure, blood
lipid levels, insulin resistance, and obesity. The type,
frequency, and intensity of physical activity that are
needed to accomplish these goals remain poorly
defined and controversial.

Physical activity is also important in the treat-
ment of patients with CVD or those who are at
increased risk for developing CVD, including pa-
tients who have hypertension, stable angina, or pe-
ripheral vascular disease, or who have had a prior
myocardial infarction or heart failure. Physical activ-
ity is an important component of cardiac rehabilita-
tion, and people with CVD can benefit from
participation. However, some questions remain re-
garding benefits, risks, and costs associated with
becoming physically active.         *
Many factors influence adopting and maintaining

a physically active lifestyle, such as socioeconomic
status, cultural influences, age, and health status.
Understanding is needed on how such variables in-
fluence the adoption of this behavior at the individual
level. Intervention strategies for encouraging indi-
viduals from different backgrounds to adopt and
adhere to a physically active lifestyle need to be

developed and tested. Different environments such
as schools, worksites, health care settings, and the
home can play a role in promoting physical activity.
These community-level factors also need to be better
understood.

  To address these and related issues, the NIH's
National Heart, Lung, and Blood Institute and Office
of Medical Applications of Research convened a
Consensus Development Conference on Physical
Activity and Cardiovascular Health. The conference
was cosponsored by the NIH's National Institute of
Child Health and Human Development, National
Institute on Aging, National Institute of Arthritis and
Musculoskeletal and Skin Diseases, National Insti-
tute of Diabetes and Digestive and Kidney Diseases,
National Institute of Nursing Research, Office of
Research on Women's Health, and Office of Disease
Prevention, as well as the Centers for Disease Con-
trol and Prevention and the President's Council on
Physical Fitness and Sports.

The conference brought together specialists in
medicine, exercise physiology, health behavior, epi-
demiology, nutrition, physical therapy, and nursing
as well as representatives from the public. After a day
and a half of presentations and audience discussion,
an independent, non-Federal consensus panel
weighed the scientific evidence and developed a
draft statement that addressed the following five
questions.

o What is the health burden of a sedentary lifetyle
on the population?

o What type, what intensity, and what quantity of
physical activity are important to prevent car-
diovascular disease?

o What are the benefits and risks of different
types of physical activity for people with car-
diovascular disease?

o What are the successful approaches to adopting
and maintaining a physically active lifestyle?
o What are the important questions for future
research?

1. What Is the Health Burden of a Sedentary
Lifestyle on the Population?

Physical inactivity among the U.S. population is now
widespread. National surveillance programs have
documented that about one in four adults (more


Historical Background, Terminology, Evolution of Recommendations, and Measurement

,,.omen than men) currently have sedentary lifestyles
\vitii no leisure time physical activity. An additional
one-third of adults are insufficiently active to achieve
health benefits. The prevalence of inactivity varies by
gctrder, age, ethnicity, health status, and geographic
region but is common to all demographic groups.
cll;lngc in physical exertion associated with occupa-
lioti has declined markedly in this century.
Girls become less active than do boys as they grow
older. Children become far less active as they move
through adolescence. Obesity is increasing among
cliildrcn, at least in part related to physical inactivity.
I>;it;t indicate that obese children and adolescents
llnvc a high risk of becoming obese adults, and obesity
iti adulthood is related to coronary artery disease,
liyI"rtcnsion, and diabetes. Thus, the prevention of
childhood obesity has the potential of preventing
(:\lD in adults. At age 12,70 percent of children report
I';trticipation in vigorous physical activity; by age 21
lllis activity falls to 42 percent for men and 30 percent
lor lvomcn. Furthermore, as adults age, their physical
;lc.tivity lcvcls continue to decline.
Although knowledge about physical inactivity as
;I risk factor for CVD has come mainly from investiga-
11ons of middle-aged, white men, more limited evi-
tlcncc from studies in women minority groups and the
c.ltlcrly suggests that the findings are similar in these
;J'OLIIX. On the basis of current knowledge, we must
I~OIC that physical inactivity occurs disproportion-
.t~cly among Americans who are not well educated and
wlro ;II-c socially or economically disadvantaged.
  Physical activity is directly related to physical
Iitucss. Although the means of measuring physical
.rctivity have varied between studies (i.e., there is no
~t:iildardization of measures), evidence indicates that
l'li?sical inactivity and lack of physical fitness are
tlirecrly associated with increased mortality from
(Ii'D. The increase in mortality is not entirely ex-
iJl;tined by the association with elevated blood pres-
`tire. smoking, and blood lipid levels. '
  There is an inverse relationship between mea-
`tires of physical activity and indices of obesity in
rll~`st U.S. population studies. Only a few studies
hive examined the relationship between physical
Jctivity and body fat distribution, and these suggest
~`1 inverse relationship between levels of physical
CIctivitv and visceral fat. There is evidence that in-
< re~isco physical activity facilitates weight loss and

that the addition of physical activity to dietary en-
ergy restriction can increase and help to maintain
loss of body weight and body fat mass.
Middle-aged and older men and women who
engage in regular physical activity have significantly
higher high-density lipoprotein (HDL) cholesterol
levels than do those who are sedentary. When exercise
training has extended to at least 12 weeks, beneficial
HDL cholesterol level changes have been reported.
  Most studies of endurance exercise training of
individuals with normal blood pressure and those
with hypertension have shown decreases in systolic
and diastolic blood pressure. Insulin sensitivity is
also improved with endurance exercise.
  A number of factors that affect thrombotic
function-including hematocrit, fibrinogen, plate-
let function, and fibrinolysis-are related to the risk
of CVD. Regular endurance exercise lowers the risk
related to these factors.

The burden of CVD rests most heavily on the
least active. In addition to its powerful impact on the
cardiovascular system, physical inactivity is also
associated with other adverse health effects, includ-
ing osteoporosis, diabetes, and some cancers.

2. What Type, What Intensity, and What
Quantity of Physical Activity Are Important
to Prevent Cardiovascular Disease?

Activity that reduces CVD risk factors and confers
many other health benefits does not require a struc-
tured or vigorous exercise program. The majority of
benefits of physical activity can be gained by per-
forming moderate-intensity activities. The amount
or type of physical activity needed for health benefits
or optimal health is a concern due to limited time and
competing activities for most Americans. The amount
and types of physical activity that are needed to
prevent disease and promote health must, therefore,
be clearly communicated, and effective strategies
must be developed to promote physical activity to
the public.

The quantitative relationship between level of
activity or fitness and magnitude of cardiovascular
benefit may extend across the full range of activity. A
moderate level of physical activity confers health
benefits. However, physical activity must be per-
formed regularly to maintain these effects.

43


Physical Activity and Health

Moderate=intensity activity performed by previously
sedentary individuals results in significant improve-
ment in many health-related outcomes. These mod-
erate intensity activities are more likely to be
continued than are-high-intensity activities.
We recommend that all people in the United
States increase their regular physical activity to a
level appropriate to their capacities, needs, and inter-
est. We recommend that all children and adults
should set a long-term goal to accumulate at least 30
minutes or more of moderate-intensity physical ac-
tivity on most, or preferably all, days of the week.
Intermittent or shorter bouts of activity (at least 10
minutes), includingoccupaiional, nonoccupational,
or tasks of daily living, also have similar cardiovascu-
lar and health benefits if performed at a level of
moderate intensity (such as brisk walking, cycling,
swimming, home repair, and yardwork) with an
accumulated duration of at least 30 minutes per day.
People who currently meet the recommended mini-
mal standards may derive additional health and
fitness benefits from becoming more physically ac-
tive or including more vigorous activity.
  Some evidence suggests lowered mortality with
more vigorous activity, but further research is needed
to more specifically define safe and effective levels.
The most active individuals have lower cardiovascu-
lar morbidity and mortality rates than do those who
are least active; however, much of the benefit appears
to be accounted for by comparing the least active
individuals to those who are moderately active. Fur-
ther increases in the intensity or amount of activity
produce further benefits in some, but not all, param-
eters of risk. High-intensity activity is also associated
with an increased risk of injury, discontinuation of
activity, or acute cardiac events during the activity.
Current low rates of regular activity in Americans
may be partially due to the mis-perception of many
that vigorous, continuous exercise is necessary to
reap health benefits. Many people, for example, fail
to appreciate walking as "exercise" or to recognize
the substantial benefits of short bouts (at least 10
minutes) of moderate-level activity.
  The frequency, intensity, and duration of activ-
ity are interrelated. The number of episodes of
activity recommended for health depends on the
intensity and/or duration of the activity: higher

intensity or longer duration activity could be per-
formed approximately three times weekly and
achieve cardiovascular benefits, but low-intensity
or shorter duration activities should be performed
more often to achieve cardiovascular benefits.
The appropriate type of activity is best deter-
mined by the individual's preferences and what will
be sustained. Exercise, or a structured program of
activity, is a subset of activity that may encourage
.interest and allow for more vigorous activity. People
who perform more formal exercise (i.e., structured
or planned exercise programs) can accumulate this
daily total through a variety of recreational or sports
activities. People who are currently sedentary or
minimally active should gradually build up to the
recommended goal of 30 minutes of moderate activ-
ity daily by adding a few minutes each day until
reaching their personal goal to reduce the risk asso-
ciated with suddenly increasing the amount or inten-
sity of exercise. (The defined levels of effort depend
on individual characteristics such as baseline fitness
and health status.)

Developing muscular strength and joint flexibil-
ity is also important for an overall activity program to
improve one's ability to perform tasks and to reduce
the potential for injury. Upper extremity and resis-
tance (or strength) training can improve muscular
function, and evidence suggests that there may be
cardiovascular benefits, especially in older patients
or those with underlying CVD, but further research
and guidelines are needed. Older people or those
who have been deconditioned from recent inactivity
or illness may particularly benefit from resistance
training due to improved ability in accomplishing
tasks of daily living. Resistance training may contrib-
ute to better balance, coordination, and agility that
may help prevent falls in the elderly.

Physical activity carries risks as well as benefits.
The most common adverse effects of activity relate to
musculoskeletal injury and are usually mild and self-
limited. The risk of injury increases with increased
intensity, frequency, and duration of activity and
also depends on the type of activity. Exercise-related
injuries can be reduced by moderating these param-
eters. A more serious but rare complication of activ-
ity is myocardial infarction or sudden cardiac death.
Although persons who engage in vigorous physical

33


Historical Background, Terminology, Evolution of Recommendations, and Measurement

.lcti\.ity have a slight increase in risk of sudden
c.lrdiac death during activity, the health benefits
c,,lttvcigh this risk because of the large overall risk
reduction.

In children and young adults, exertion-related
dcarhs are uncommon and are generally related to
cangcnital heart defects (e.g., hypertrophic cardi-
,,mvopathy, Marfan's syndrome, severe aortic valve
,lc1I()sis. prolonged QT syndromes, cardiac conduc-
lloll abnormalities) or to acquired myocarditis. It is
rcc(>mmcnded that patients with those conditions
rclnGlin ilctive but not participate in vigorous or
c.~~lllpctitivc athletics.

BKWSC the risks of physical activity are very low
c.(,lnp;lrcd with the health benefits, most adults do
[lot uccd medical consultation or pretesting before
\r;lrtirig a moderate-intensity physical activity pro-
,<r;lln. However, those with known CVD and men
,)~cr :tgc -to and women over age 50 with multiple
I ;lrdiovascular risk factors who contemplate a pro-
c:r-am of vigorous activity should have a medical
t.\..lIu;ltion prior to initiating such a program.

3. What Are the Benefits and Risks of
Different Types of Physical Activity for
People with Cardiovascular Disease?

Xlorc than 10 million Americans are afflicted with
( lillically significant CVD, including myocardial in-
I.lrction, angina pectoris, peripheral vascular dis-
(`:Iw. and congestive heart failure. In addition, more
I~KU~ 300,000 patients per year are currently sub-
~.tccl to coronary artery bypass surgery and a similar
~~~~mbcr to percutaneous transluminal coronary
.+$@asty. Increased physical activity appears to
h~ncfit each of these groups. Benefits include reduc-
ll(~n in cardiovascular mortality, reduction of symp-
l~~lll~, improvement in exercise tolerance and
Illnctional capacity, and improvement in psycho-
I~)gicul well-being and quality of life.
jcw-al studies have shown that exercise training

IJWran= significantly reduce overall mortality, as
~~11 as death caused by myocardial infarction. The
Vl~rtcd reductions in mortality have been highest-
Wroximately 25 percent-in cardiac rehabilitation
19Wms that have included control of other cardio-
\`ascular risk factors. Rehabilitation programs using
`~(~111 moderate and vigorous physical activity have

been associated with reductions in fatal cardiac events,
although the minimal or optimal level and duration
of exercise required to achieve beneficial effects
remains uncertain. Data are inadequate to determine
whether stroke incidence is affected by physical
activity or exercise training.

The risk of death during medically supervised
cardiac exercise training programs is very low. How-
ever, those who exercise infrequently and have poor
functional capacity at baseline may be at somewhat
higher risk during exercise. training. All patients
with CVD should have a medical evaluation prior to
participation in a vigorous exercise program.
Appropriately prescribed and conducted exer-
cise training programs improve exercise tolerance
and physical fitness in patients with coronary heart
disease. Moderate as well as vigorous exercise train-
ing regimens are of value. Patients with low basal
levels of exercise capacity experience the most func-
tional benefits, even at relatively modest levels of
physical activity. Patients with angina pectoris typi-
cally experience improvement in angina in associa-
tion with a reduction in effort-induced myocardial
ischemia, presumably as a result of decreased myo-
cardial oxygen demand and increased work capacity.
Patients with congestive heart failure also appear
to show improvement in symptoms, exercise capac-
ity, and functional well-being in response to exercise
training, even though left ventricular systolic func-
tion appears to be unaffected. The exercise program
should be tailored to the needs of these patients and
supervised closely in view of the marked predisposi-
tion of these patients to ischemic events and
arrhythmias.

Cardiac rehabilitation exercise training often
improves skeletal muscle strength and oxidative
capacity and, when combined with appropriate nu-
tritional changes, may result in weight loss. In addi-
tion, such training generally results in improvement
in measures of psychological status, social adjust-
ment, and functional capacity. However, cardiac
rehabilitation exercise training has less influence on
rates of return to work than many nonexercise vari-
ables, including employer attitudes, prior employ-
ment status, and economic incentives. Multifactorial
intervention programs, including nutritional changes
and medication plus exercise, are needed to improve
health status and reduce cardiovascular disease risk.

45


Physical Activity and Health

Cardiac rehabilitation programs have tradition-
ally been institutional-based and group-centered (e.g.,
hospitals, clinics, community centers>. Referral and
enrollment rates have been relatively low, generally
ranging from 10 to 25 percent of patients with CHD.
Referral rates are lower for women than for men and
lower for non-whites than for whites. Home-based
programs have the potential to provide rehabilitative
services to a wider population. Home-based pro-
grams incorporating limited hospital visits with regu-
lar mail or telephone followup by a nurse case
manager have demonstrated significant increases in
functional capacity, smokingcessation, and improve-
ment in blood lipid levels. A range of options exists
in cardiac rehabilitation including site, number of
visits, monitoring, and other services.
  There are clear medical and economic reasons
for carrying out cardiac rehabilitation programs.
Optimal outcomes are achieved when exercise train-
ing is combined with educational messages and
feedback about changing lifestyle. Patients who par-
ticipate in cardiac rehabilitation programs show a
lower incidence of rehospitalization and lower
charges per hospitalization. Cardiac rehabilitation is
a cost-efficient therapeutic modality that should be
used more frequently.

4. What Are the Successful Approaches to
Adopting and Maintaining a Physically
Active Lifestyle?
The cardiovascular benefits from and physiological
reactions to physical activity appear to be similar
amongdiverse populationsubgroupsdefined by age,
sex, income, region of residence, ethnic background,
and health status. However, the behavioral and atti-
tudinal factors that influence the motivation for and
ability to sustain physical activity are strongly deter-
mined by social experiences, cultural background,
and physical disability and health status. .For ex-
ample, perceptions of appropriate physical activity
differ by gender, age, weight, marital status, family
roles and responsibilities, disability, and social class.
Thus, the following general guidelines will need to
be further refined when one is planning with or
prescribing for specific individuals and population
groups, but generally physical activity is more likely
to be initiated and maintained if the individual

.


.


.


.


.


.


.




.






.




.

Perceives a net benefit.

Chooses an enjoyable activity.
Feels competent doing the activity.
Feels safe doing the activity.
Can easily access the activity on a regular basis.
Can fit the activity into the daily schedule.
Feels that the activity does not generate financial
or social costs that he or she is unwilling to bear.
Experiences a minimum of negative conse-
quences such as injury, loss of time, negative
peer pressure, and problems with self-identity.
Is able to successfully address issues of compet-
ing time demands.

Recognizes the need to balance the use of labor-
saving devices (e.g., power lawn mowers, golf
carts,automobiles) andsedentaryactivities (e.g.,
watching television, use of computers) with
activities that involve a higher level of physical
exertion.

Other people in the individual's social environ-
ment can influence the adoption and maintenance of
physical activity. Health care providers have a key
role in promoting smoking cessation and other risk-
reduction behaviors. Preliminary evidence suggests
that this also applies to physical activity. It is highly
probable that people will be more likely to increase
their physical activity if their health care provider
counsels them to do so. Providers can do this effec-
tively by learning to recognize stages of behavior
change, to communicate the need for increased ac-
tivity, to assist the patient in initiating activity, and
by following up appropriately.
Family and friends can also be important sources
of support for behavior change. For example, spouses
or friends can serve as "buddies," joining in the
physical activity; or a spouse could offer to take on a
household task, giving his or her mate time to engage
in physical activity. Parents can support their
children's activity by providing transportation, praise,
and encouragement, and by participating in activi-
ties with their children.

Worksites have the potential to encourage in-
creased physical activity by offering opportunities,
reminders, and rewards for doing so. For example,
an appropriate indoor area can be set aside to enable
walking during lunch hours. Signs placed near

46


Historical Background, Terminology, Evolution of Recommendations, and Measurement

clcvators can encourage the use of the stairs instead.
Discounts on parking fees can be offered to employ-
ccs who elect to park in remote lots and walk.

Schools are a major community resource for
increasing physical activity, particularly given the
nrgent need to develop strategies that affect children
;rnd adolescents. As noted previously, there is now
cfcar evidence that U.S. children and adolescents
bavc become more obese. There is also evidence that
c,besc children and adolescents exercise less than
their leaner peers. All schools should provide oppor-
tunities for physical activities that

Arc appropriate and enjoyable for children of
all skill levels and are not limited to competitive
sports or physical education classes.
Appeal to girls as well as to boys, and to children
from diverse backgrounds.
Can serve as a foundation for activities through-
out life.

Arc offered on a daily basis.
5uccessful approaches may involve mass educa-

INHI strategies or changes in institutional policies or
c.ommunity variables. In some environments (e.g.,
s~.h~~ols, worksites, community centers), policy-level
llrtcrventions may be necessary to enable people to
;rl.tlicvc and maintain an adequate level of activity.
~`cbltcy changes that increase opportunities for physi-
I .rI irctivity can facilitate activity maintenance for
Illotivatcd individuals and increase readiness to
c II;III~C' among the less motivated. As in other areas
01 health promotion, mass communication strate-
~1~s should be used to promote physical activity.
I Ircsc strategies should include a variety of main-
\trc:nn channels and techniques to reach diverse
.~nclicnccs that acquire information through differ-
(`rlt media (e.g., TV, newspaper, radio, Internet).

5. What Are the Important Considerations
for Future Research?
\\`hilc much has been learned about the role of
I~h!.~ical activity in cardiovascular health, there are
rrr~~rrv unanswered questions.
  o Maintain surveillance of physical activity levels
in the U.S. population by age, sex, geographic,
  and socioeconomic measures.

Develop better methods for analysis and quan-
tification of activity. These methods should be
applicable to both work and leisure time mea-
surements and provide direct quantitative esti-
mates of activity.

Conduct physiologic, biochemical, and genetic
research necessary to define the mechanisms
by which activity affects CVD including changes
in metabolism as well as cardiac and vascular
effects. This will provide new insights into
cardiovascular biology that may have broader
implications than for other clinical outcomes.
Examine the effects of physical activity and
cardiac rehabilitation programs on morbidity
and mortality in elderly individuals.

Conduct research on the social and psychologi-
cal factors that influence adoption of a more
active lifestyle and the maintenance of that
behavior change throughout life.

Carry out controlled randomized clinical trials
among children and adolescents to test the
effects of increased physical activity on CVD
risk factor levels including obesity. The effects
of intensity, frequency, and duration of in-
creased physical activity should be examined in
such studies.

Conclusions

Accumulatingscientific evidence indicates that physi-
cal inactivity is a major risk factor for CVD. Moderate
levels of regular physical activity confer significant
health benefits. Unfortunately, most Americans have
little or no physical activity in their daily lives.

All Americans should engage in regular physical
activity at a level appropriate to their capacities,
needs, and interests. All children and adults should
set and reach a goal of accumulating at least 30
minutes of moderate-intensity physical activity on
most, and preferably all, days of the week. Those who
currently meet these standards may derive additional
health and fitness benefits by becoming more physi-
cally active or including more vigorous activity.

Cardiac rehabilitation programs that combine
physical activity with reduction in other risk factors
should be more widely applied to those with known
CVD. Well-designed rehabilitation programs have

47


Physical Activity and Health

benefits that are lost because of these programs'
limited use.

  Individuals with CVD and men over 40 or women
over 50 years of age with multiple cardiovascular risk
factors should have a medical evaluation prior to
embarking on a vigorous exercise program.
Recognizing the importance of individual and
societal factors in initiating and sustaining regular
physical activity, the panel recommends the following:
o Development of programs for health care pro-
  viders to communicate to patients the impor-
  tance of regular physical activity.
o Community support of regular physical activ-
  ity with environmental and policy changes at
  schools, worksites, community centers, and
   other sites.

o Initiation of a coordinated national campaign
involving a consortium of collaborating health
organizations to encourage regular physical
activity.

o The implementation of the recommendations
in this statement has considerable potential to
improve the health and well-being of American
citizens.

About the NIH Consensus
Development Program
NIH Consensus Development Conferences are con-
vened to evaluate available scientific information
and resolve safety and efficacy issues related to a
biomedical technology. The resultant NIH Consen-
sus Statements are intended to advance understand-
ing of the technology or issue in question and to be
useful to health professionals and the public.

48


Historical Background, Terminology, Evolution of Recommendations, and Measurement

References

Acheson KJ, Campbell lT, Edholm OG, Miller DS, Stock
\[J. The measurement of daily energy expenditure: an
evaluation of some techniques. American Journal of
C/i~~ic~ll Nutrition 1980;33: 1155-l 164.

,\insworth BE, Montoye HJ, Leon AS. Methods of assess-
Ing physical activity during leisure and work. In:
Bouchard C, Shephard RJ,Stephens T, editors. Physical
activity, fitness, and health: international proceedings
& C~IISC~SUS statement. Champaign, IL: Human Ki-
nctics, 1994: 146-159.

.\lh~~cs D, Conway JM, Taylor PR, Moe PW, Judd J.
\`;llidation and comparison of eight physical activity
questionnaires. Epidemiology 1990;1:65-71.

,.\llcn W, Pepys WH. On respiration. Philosophical Transac-
lions OJLJIC Royal Society ojLondon 1809(Pt 2):404-429.

.\lucrican Academy of Pediatrics, Committee on Sports
Mcdicinc and Fitness. Assessing physical activity and
lltncss in the office setting. Pediatrics 1994;93:686-689.

.\ltlcrican Academy of Pediatrics, Committee on Sports
blvlrrlicinc and Fitness. Fitness, activity, and sports
p;lrticipation in the preschool child. Pediatrics
I992;c)O: 1002-1004.

.\lllcrican Association of Cardiovascular and Pulmonary
I~~~habilitation. Guidelinesjorcardiac rehabilitationpro-
,<I NJJS. Champaign, IL: Human Kinetics, 1991.

.\rJtc~~~l Association of Cardiovascular and Pulmonary
I:cllahilitation. GuidelinesJar pulmonary rehabilitation
~IJ~NJJS. Champaign, IL: Human Kinetics, 1993.

.\~~~LT~LxI Association of Cardiovascular and Pulmonary
i~~hubilitation. Guidelines for cardiac rehabilitation
IJ~[JSKCJJK 2nd ed. Champaign, IL: Human Kinetics, 1995.
.\nlcrican College of Sports Medicine. ACSM position
\t:md on osteoporosis and exercise. Medicine and Sci-
(`)u`(' it1 Sports and Exercise 1995a;27:i-vii.

\Illcrican College of Sports Medicine. ACSM's guidelines
1~1~~l'-~cJ-cisc testing and prescription. 5th ed. Baltimore:
\i'illiams and Wilkins, I995b.

.\mcrican College of Sports Medicine. Gtiidelines/or exer-
tisc tcstitlg and prescription. 3rd ed. Philadelphia: Lea
Lmd Fcbiger, 1986.

-`lncrlcan College of Sports Medicine. Guidelinesfor exer-
t IQ fcs% atld prescription. 4th ed. Philadelphia: Lea
.lml Fcbiger, 1991.

""crican College of Sports Medicine. Guidelinesforgraded
".Ycrcisc testing and exercise prescription. Philadelphia:
&I and Febiger, 1975.

American College of Sports Medicine. Guidelinesforgraded
exercise testing and exercise prescription. 2nd ed. PhiIa-
delphia: Lea and Febiger, 1980.

American College of Sports Medicine. Physical activity,
physical fitness, and hypertension. Medicine and Sci-
ence in Sports and Exercise 1993;25:i-x.

American College of Sports Medicine. Position stand:
exercise for patients with coronaryarterydisease. Medi-
cine and Science in Sports and Exercise 1994;26:i-v.

American College of Sports Medicine. Position stand: the
recommended quantity and qvality of exercise for
developing and maintaining cardiorespiratory and
muscular fitness in healthy adults. Medicine and Sci-
ence in Sports and Exercise 1990;22:265-274.

American College of Sports Medicine. The recommended
quantity and quality of exercise for developing and
maintaining fitness in healthy adults. Medicine and
Science in Sports 1978;1O:vii-x.

American Heart Association. Cardiac rehabilitation pro-
grams: astatement for healthcare professionals from the
American Heart Association. Circulation 1994;90: 1602-
1610.

American Heart Association. Exercise standards: a state-
ment for healthcare professionals from the American
Heart Association. Circulation 1995;91:580-615.

American Heart Association. Exercise testing and training
of apparently healthy individuals: a handboohfor physi-
cians. Dallas: American Heart Association, 1972.

American Heart Association. Exercise testing and training
of individuals with heart disease or at high risk for its
development: a handboohfor physicians. Dallas: American
Heart Association, 1975.

American Heart Association. Statement on exercise: ben-
efits and recommendations for physical activity pro-
grams for all Americans: a statement for health
professionals by the Committee on Exercise and Car-
diac Rehabilitation of the Council on Clinical Cardiol-
ogy, American Heart Association. Circulation
1992;86:340-344.

American Heart Association, Blair SN, Powell KE, Bazzarre
TL, EarlyJL, Epstein LH, et al. AHAprevention confer-
ence. III. Behavior change and compliance: key to
improving cardiovascular health. Physical inactivity:
workshop V. Circularion 1993;88:1402-1405.

American Medical Association, Elster AB, Kuznets NJ.
AMA guidelinesforadolescent preventive services (GAPS):
recommendations and rationale. Chicago, IL: Williams
and Wilkins, 1994.

49


.Physical Activity and Health

Balogun JA, Amusa LO, Onyewadume IU. Factors affect-
ing Caltrac@ and Calcount@ accelerometer output.
Physical Therapy 1988;68: 1500-l 504.

Baranowski T. Methodologic issues inself-report ofhealth
behavior.Journal ofSchool Health 1985;55:179-182.

Beecher CE. Physiology and calisthenics for schools and
families. New York: Harper and Brothers, 1856.

Benedict FG, Cathcart EP. Muscular work a metabolic
study with special reJerence to the efficiency ofthe human
body as a machine. Washington, DC: Carnegie Institu-
tion of Washington, 1913.

Berryman JW. Exercise and the medical tradition from
Hippocrates through antebellum America: a review
essay. In: Berryman JW, Park RJ, editors. Sport and
exercise science: essays in the history ofsports medicine.
Urbana, IL: University of Illinois Press, 1992:1-56.

Berryman JW. Out of many, one: a hijtory of the American
College 01 Sports Medicine. Champaign, IL: Human
Kinetics, 1995.

Bierman EL, Brunzell JD. Obesity and atherosclerosis. In:
Bjijrntorp P, Brodoff BN, editors. Obesity. Philadel-
phia: J.B. Lippincott Company, 1992:512-516.

Blair SN. 1993 C.H. McCloy research lecture: physical
activity, physical fitness, and health. Research Quar-
terly for Exercise and Sport 1993;64:365-376.

Blair SN, Dowda M, Pate RR, Kronenfeld J, Howe HG Jr,
Parker G, et al. Reliability of long-term recall of participa-
tion in physical activity by middle-aged men and women.
Americanjournal ofEpidemiology 1991;133:266-275.

Blair SN, Falls HB, Pate RR. A new physical fitness test.
Physician and Sportsmedicine 1983;11:87-95.

Blair SN, Kannel WB, Kohl HW, Goodyear N, Wilson
PWF. Surrogate measures of physical activity and
physical fitness: evidence for sedentary traits of resting
tachycardia, obesity, and low vital capacity. American
journal of Epidemiology 1989;129:1145-1156.

Blair SN, Kohl HW, Gordon NF. How much physical
activity is good for health? Annual Reviews of Public
Health 1992;13:99-126.

Blair SN, Kohl HW III, Paffenbarger RS Jr, Clark DG,
Cooper KH, Gibbons LW. Physical fitness and all-
cause mortality: a prospective study of healthy men
and women. Journal of the American Medical Associa-
tion 1989;262:2395-2401.

Blumberg VS, Alexander J. Obesity and the heart. In:
Bjiirntorp P, Brodoff BN, editors. Obesity. Philadel-
phia: J.B. Lippincott Company, 1992:5 17-53 1.

Borg GA. Psychophysical bases of perceived exertion.
MedicineandScienceinSportsandExercise 1982;14:377-
381.

Bouchard C, Shephard RJ, Stephens T, editors. Physical
activity, fitness, and health: international proceedings
and consensus statement. Champaign, IL: Human Ki-
netics, 1994.

Bouchard C, Shephard RJ, Stephens T, Sutton JR,
McPherson BD. Exercise, fitness, and health: the con-
sensus statement. In: Bouchard C, Shephard RJ,
Stephens T, Sutton JR, McPher!on BD, editors. Exer-
cise,Jitness, and health. Champaign, IL: Human Kinet-
ics, 1990:4-28.

Brown RG, Davidson LAG, McKeown T, Whitfield AGW.
Coronary-artery disease- influences affecting its inci-
dence in males in the seventh decade. Lancet
1957;2:1073-1077.

Buchan W. Domestic medicine: or, a treatiseon theprevention
and cure of diseases, by regimen and simple medicines
[ 1769). Reprint, Boston: Joseph Bumstead, 1813.

Burns CR. The nonnaturals: a paradox in the western
concept of health. Journal of Medicine and Philosophy
1976;1:202-211.

Byford WH. On the physiology of exercise. American
Journal of Medical Sciences 1855;30:32-42.

Bylebyl JJ. The school of Padua: humanistic medicine in
the sixteenth century. In: Webster C, editor. Health,
medicine, andmortality in rhe sixteenth century. Cambridge,
MA: Cambridge University Press, 1979:335-370.

Caldwell C. Thoughts on physical education: being a dis-
course delivered to a convention ofteachers in Lexington,
Kentucky, on the 6th and 7th ofNovember 1833. Boston:
Marsh, Capen, and Lyon, 1834.

Caspersen CJ. Physical activity epidemiology: concepts,
methods, and applications to exercise science. Exercise
and Sport Sciences Reviews 1989;17:423-473.

Caspersen CJ, Pollard RA. Validity of global self-reports of
physical activity in epidemiology. CVD Epidemiology
Newsletter 1988;43:15.

Caspersen CJ, Powell KE, Christensen GM. Physical ac-
tivity, exercise, and physical fitness: definitions and
distinctions for health-related research. Public Health
Reports 1985;100:126-131.

Cassedy JH. Why self-help? Americans alone with their
diseases, 1800-1850. In: Risse GB, Numbers RL, Leavitt
JW, editors. Medicine without doctors: home health cure
in American history. New York: Science History Publi-
cations, 1977:31-48.

50


Historical Background, Terminology, Evolution of Recommendations, and Measurement

Chapman CB, Mitchell JH. The physiology of exercise.
Scicnt$ic America 1965;212:88-96.
Chcyne G. An essay ofhealth and fang fije ]1724]. Reprint,
London: George Strahan, 1734.

Christensen EH. Intervallarbeit und intervalltraining.
Zi&itsphysiofogie 1960;18:345-356.
Clarke HH, editor. Toward a better understanding of
muscular strength. Physical Fitness Research Digest
1973;3:1-20.

Cogm T. The haven oj health [ 15841. Reprint, London:
Bonham Norton, 1596.

<looper KH. A means of assessing maximal oxygen intake:
correlation between field and treadmill testing.Joumal
(JI tflc American Medical Association 1968;203:135-
138.

Corbin CB, Lindsey R. Concepts in physical education
with laboratories. 8th ed. Dubuque, IA: Times Mirror
tiigher Education Group, 1494.

(:ornaro L. The art of living long (15581. Reprint, Mil-
waukee: William F. Butler, 1905.

( r;unpton CW. A test of condition: preliminary report.
Mcdicaf News 1905;87:529-535.

( :rarnpton CW. Start today: your guide to physical fitness.
New York: A.S. Barnes, 1941.

(.nrcton TK. Physicalfitness workbook: a manual ofcondi-
riorlirlg exercises and standards, tests, and rating scales
/of- cvctfuating physical fitness. 3rd ed. St. Louis: C.V.
Mosby Company, 1947.

(.yrias RJ. A short history of mechano-therapeutics in
Europe until the time ofLing.Janus 1914;19:178-240.

I)cl%ackcr G, Kornitzer M, Sobolski J, Dramaix M, Degre
5. dc Marnelfe M. Physical activity and physical fitness
fcvcls of Belgian males aged 40-55 years. Cardiology
1981;67:110-128.

1)111 DB. The Harvard Fatigue Laboratory: its develop-
ment, contributions, and demise. In: Chapman CB,
editor. Physiology of muscular exercise. New York:
American Heart Association, 1967.
I)iPictro L, Caspersen CJ, Ostfeld AM, Nadel ER. A survey
for assessing physical activity among older adults. Medi-
ciflc and Science in Sports and Exercise 1993;25:62%642.
[)ishman RK, editor. Exerciseadherence: its impact on public
hcuftf~. Champaign, IL: Human Kinetics, 1988.
l)uhfin L. Longevity of college athletes. Statistical Bulletin
cJf[flc Metropofitan Insurance Company 1932;13:5-7.

Eaton SB, Shostak M, Konner M. The Paleolithic prescrip-
tion:aprogramofdiet andexerciseandadesignforfiving.
New York: Harper and Row, 1988.
EdwardsJE. StagerJM, Updyke W, Elizondo R. Validity of
the doubly labeled water method of measuring energy
expenditure with rest and exercise in non-human
primates. Medicine and Science in Sports and Exercise
1990;22:550-557.

Fitz GW. Principles ofphysiology and hygiene. New York:
H. Hoft and Company, 1908.
Fishbein M. A history ofthe American Medical Association,
1847 to 1947. Philadelphia:-W.B. Saunders, 1947.

Fishbein M. Health of young men under selective service.
Journal OftheAmericanMedicaf Association 1941;116:54-
55.

Fletcher GF, Blair SN, Blumenthal J, Caspersen C,
Chaitman B, Epstein S, et al. Statement on exercise:
benefits and recommendations for physical activity
programs for all Americans: a statement for health
professionals by the Committee on Exercise and Car-
diac Rehabilitation of the Council on Clinical Cardiol-
ogy, American Heart Association. Circulation
1992;86:340-344.

Foster WL. A test of physical efficiency. American Physical
Education Review 1914;19:632-636.

Freedson PS. Field monitoring of physical activity in
children. Pediatric Exercise Science 1989;1:8-18.

Gemmill C, Booth W, Detrick J, Schiebel H. Muscular
training. II. The effects of training on the recovery
period following severe muscular exercise. American
Journal of Physiology 1931;96:265-277.

Gilliam TB, Freedson PS, Geenen DL, Shahraray B. Physi-
cal activity patterns determined by heart rate monitor-
ing in 6-7 year-old children. Medicine and Science in
Sports and Exercise 1981;13:65-67.
Green RM. A translation of Gafen's hygiene (De sanitate
tuenda). Springfield, IL: Charles C. Thomas, 1951.

Gruman GJ. The rise and fall of prolongevity hygiene,
1558-1873. Bulletin of the History oJ Medicine 1961;
35:221-229.

Gunn JC. Gunn's domestic medicine, or poor man's friend
[ 18301. Reprint, with an introduction by Charles E.
Rosenberg. Knoxville, TN: University of Tennessee
Press, 1986.

Hackensmith CW. History of physical education. New
York: Harper and Row, 1966.

51


Physical Activity and Health

Harris ML. A factor analytic study of flexibility. Research
Quarterly 1969;40:62-70.

Harris SS, Caspersen CJ, DeFriese GH, Estes EH Jr. Physical
activity counseling for healthy adults as a primary
preventive intervention in the clinical setting: report for
the U.S. Preventive Services Task Force. Journal of the
American Medical Association 1989;261:3588-3598.

Hartwell EM. On the physiology of exercise. Boston Medical
andSurgicaf]oumaf 1887;116:13:297-302.

Haskell WL. Physical activity and health: the need to define
the required stimulus. American Journal of Cardiology
1984;55:4D-YD.

Haskell WL, Yee MC, Evans A, lrby PJ. Simultaneous mea-
surement of heart rate and body motion to quantitate
physical activity. Medicine and Science in Sports and Exer-
cise 1993;25:109-115.

Hill AV. Living machinery: eight lectures defiveredat theLowell
Institute, Boston, March 1927. New Yolk: Harcourt, Brace,
and Company, 1927.

Hill AV. Muscular activity. Baltimore: Williams and
Wilkins, 1926.

Hill AV. The physiological basis ofathletic records. Lancet
1925a;2:481-486.

Hill AV. The physiological basis ofathletic records. Scien-
tific Monthly 1925b;21:409-428.

Hippocrates. Regimen 1. Translated by W.H.S. Jones. Cam-
bridge, MA: Harvard University Press, 1953.

Hitchcock E. Elementary anatomy and physiology. Rev. ed.
New York: Ivison, Phinney, 1861.

Horvath SM, Horvath EC. The Harvard Fatigue Labora-
tory: its history andcontributions. Englewood Cliffs, NJ:
Prentice-Hall, 1973.

Huang Ti. Nei Ching Su Wen: the Yellow Emperor's classic
of intcrnaf medicine. Translated by Ilza Veith. Balti-
more: Williams and Wilkins, 1949.

Huard P, Wong M. Chinese medicine. Translated by
Bernard Fielding. London: Weidenfeld and Nicolson,
1968.

Jacobs DR, Ainsworth BE, Hartman TJ, Leon AS. A simul-
taneous evaluation of 10 commonly used physical
activity questionnaires. Medicine and Science in Sports
and Exercise 1993;25:81-91.

Jaeger W. Paideia: rhe ideals ofGreekculture. Translated by
Gilbert Highet. Vol. 1. Archaic Greece-the mind of
Athens. 2nd ed. New York: Oxford University Press,
  1965.

Kannel WB, Wilson P, Blair SN. Epidemiological assess-
ment of the role of physical activity and fitness in
development of cardiovascular disease. American Heart
Journal 1985;109:876-885.

Karvonen MJ, Kentala E, Mustala 0. The effects of training
on heart rate. Acta Medica Exp Fenn 1957;35:308-315.

Kashiwazaki H, Inaoka T, Suzuki T, Kondo Y. Correla-
tions of pedometer readings with energy expenditure
in workers during free-living daily activities. European
Journal of Applied Physiology 1986;54:585-590.

Katzenstein G. Ueberdie Einwirkung.der Muskefthitigkeit
auf den Stoffverbrauch des Menschen. Pfliiger EFW.
Archiv fiir die gesammte Physiofogie des Menschen und
der Thiere. Bonn: M. Hager; 18?1:49:330-404.
King AC, Haskell WL, Taylor CB, I&aemer HC, DeBusk
RF. Group- vs home-based exercise training in healthy
older men and women: a community-based clinical
trial. Journal of the American Medical Association
1991;266:1535-1542.

Klein PD, James WPT, Wong WW, Irving CS, Murgatroyd
PR, Cabrera M, et al. Calorimetric validation of the
doubly labelled water method for determination of
energy expenditure in man. Human Nutrition, Clinical
Nutrition 1984;38(3:95-106.

Klesges LM, Klesges RC. The assessment of children's
physical activity: a comparison of methods. Medicine
and Science in Sports and Exercise 1987;19:511-517.
Knehr CA, Dill DB, Neufeld W. Training and its effects on
man at rest and at work. AmericanJournal of Physiology
1942;136:148-156.

Kraus H, Hirschland RP. Muscular fitness and health.
Journal for Health, Physical Education, and Recreation
1953;24:17-19.

Kriska AM, Sandler RB, Cauley JA, LaPorte RE, Horn DL,
Pambianco G. The assessment of historical physical
activity and its relation to adult bone parameters.
AmericanJoumalofEpidemiology 1988;127:1053-1063.

Lagrange F. Physiology of bodily exercise [ 1881. Reprint,
New York: D. Appleton, 1890.

Lakka TA, Nyyssonen K, Salonen JT. Higher levels of
conditioning leisure-time physical activity are associ-
ated with reduced levels of stored iron in Finnish men.
AmericanJournal of Epidemiology 1994;140:148-160.

Langenfeld H. Auf dem wege zur sportwissenschaft:
mediziner und leibestibungen im 19. jahrhundert.
Stadion 1988;14:125-148.

52


Historical Background, Terminology, Evolution of Recommendations, and Measurement

L.lPartc RE, Black-Sandier R. CauleyJA, LinkM, Bayles C,
\liarks B. The assessment of physical activity in older
,von,en: analysis of the interrelationship and reliability
<,f activity monitoring, activity surveys, and caloric
,ntl,kc. ~~~o-nal of Gerontology 1983;38:394-397.
I-.,Porrf RE. Montoye HJ, Caspersen CJ. Assessment of
I~t~~sica1 activity in epidemiologic research: problems
.,nd prospects. Public Health Reports 1985;100:131-
  I Sh.

,..lrsc,n LA, \`ocom RD. Measurement and eva1wation in
1+?sica1, ~~calth, and recreation education. St. Louis:
(3.~`. Mosby, 1951.

I-.,vc>;l;icr AL. Experiences sur la respiration des animaux,
l't sur 1cs changemens qui arrivent 8 I'air en passant par
Icur ponmon. Histoire de I'Acad&nie Royafe des Sci-
,.,,( `.s. Paris: AcadPmie des Sciences, 1777:185-194.

1 .ivcJisicr i\L, de LaPlace PS. Memoire sur la chaleur.
~f~%l(~~rc de I'AcadCmie Royale des Sciences. Paris:
:\c;&mic dcs Sciences, 1780:355-408.

I <llrllillln JF, Boswell S, Price R, Btirleigh A, de Lateur BJ,
1;1lf~ KM, ct al. Quantitative evaluation of sway as an
Illdic;rtor of functional balance in post-traumatic brain
~tll~lry. Archives o/Physical Medicine and Rehabilitation
I WO;i 1:955-962.

I C'OII ;\S,Jacobs DRJr, DeBacker G, Taylor HL. Relation-
ship of physical characteristics and life habits to tread-
111111 cscrcisccapacity.AmericanJouma1ofEpidemio1ogy
I OH I : I I3:653-660.

I (.IIII;IKI I:II, Afflcck GB. A guide to the history ofphysical
&cc trliorl. 3rd cd. Philadelphia: Lea and Febiger, 1947.

I V\VI~ I). 711~ new gymnasticsformen, women, and children.
New York: Clarke Brothers, 1883.

1 lc.ht 5. History [of therapeutic exercise]. In: Basmajian
11'. editor. Therapeutic exercise. 4th ed. Baltimore:
\Vi11inms and Wilkins, l984:l-44.

1 ~1hm111 TG. Applicability of body composition tech-
~ll~l"cs and constants for children and youths. Exercise
cltd sprl Sciences Reviews 1986;14:325-357.

1 ~~hm~m TG. Research progress in validation of labora-
I<? methods of assessing body composition. Medicine
(Jtd SchKC in Sports and Exercise 1984;16:596-603.
Lu~~lski HC, Bolonchuk WW, Ha11 &, Siders WA. Vali-
d&ltkm of tetrapolar bioelectric impedance method to
slsscss human body composition. Journal of Applied
f'll.vsio1o~ 1986;60:1327-1332.

"~css RB. Barden HS, Bisek JP, Hanson J. Dual-energy
s-ray absorptiometry for total-bodyandregional bone-
lnlncral and soft-tissue composition. American Journal
C'I CIitiical Nutrition 1990;5l:llO6-lll2,

McCloy CH. Physical fitness and citizenship. Journal of
Health and Physical Education 1938;9:298.
McCurdy JH. The effect of maximum muscular effort on
blood pressure. American Journal of Physiology 1901;
5:95-103.

McKenzie RT. Exercise in education and medicine. Phila-
delphia: W.B. Saunders, 1909.
McKenzie RT. The influence of exercise on the heart.
American Journal of the Medical Sciences 1913;145:
69-74.

Mendez C. Book ofbodily exercise [ 15531. translated by F.
Guerra. New Haven, CT: Elizabeth Licht. 1960.

Mercurialis H. De arte gymnastica [ 15691. 2nd ed. Paris:
Du Puys, 1577.

Mitchell JH, Blomqvist G. Maxima1 oxygen uptake. New
England Journal of Medicine 1971;284:1018-1022.
Montoye HJ. The Raymond Pearl memorial lecture, 1991:
health, exercise, and athletics: a millennium of obser-
vations-a century of research. American Journal of
Human Biology 1992;4:69-82.
Montoye HJ, Cunningham DA, Welch HG, Epstein FH.
Laboratory methods of assessing metabolic capacity in
a large epidemiologic study. American Journal ofEpide-
miology 1970;91:38-47.

Montoye HJ, Kemper HCG, Saris WHM, Washburn RA.
Measuring physical activity and energy expenditure.
Champaign, IL: Human Kinetics, 1996.
Montoye HJ, Taylor HL. Measurement ofphysical activity
in population studies: a review. Human Biology
1984;56: 195-216.

Montoye HJ, Van Huss WD, Brewer WD, Jones EM,
Ohlson MA, MaLoney E, et al. The effects of exercise
on blood cholesterol of middle-aged men. American
Journal ofClinical Nutrition 1959;7:139-145.
Morantz RM. Making women modern: middle-class
women and health reform in 19th-century America. In:
Leavitt JW, editor. Women and health in America: his-
torical readings. Madison, WI: University of Wisconsin
Press, 1984:346-358.

Morris JN, Heady JA, Raffle PAB, Roberts CG, Parks JW.
Coronary heart disease and physical activity of work.
Lancet 1953;2:1053-1057, 1111-l 120.

Nabokov P. Indian running: Native American history and
tradition. Santa Barbara, CA: Capra Press, 1981.

53


Physical Activity and Health

National Center for Health Statistics, Bloom B. Current
estimates from the National Health Interview Survey,
United States, 1981. Vital and Health Statistics: Series
10, No. 141. Hyattsville, MD: U.S. Department of
Health and Human Services, Public Health Service,
National Center for Health Statistics, 1982. DHHS
Publication No. (PHS)82-1569.

National Center for Health Statistics, Wilmore JH. Design
issues and alternatives in assessing physical fitness
among apparently healthy adults in a health examina-
tion survey of the general population. In: Assessing
physicalfitness and physical activity in population-based
surveys. Hyattsville, MD: U.S. Department of Health
and Human Services, Public Health Service, National
Center for Health Statistics, 1989:107-153. DHHS
Publication No. (PHS)89-1253.

National Council of Young Men's Christian Associations
of the United States. Y's way to physical fitness: the
complete guide to fitness testing and instruction.
Champaign, IL: Human Kinetics, 1989.

National lnstitutes of Health. Consensus development
conference statement on physical activity and cardio-
vascular health, December 20, 1995, Bethesda, MD
(draft statement).

Noland M, Danner F, DeWalt K, McFadden M, Kotchen
JM. The measurement of physical activity in young
children. Research Quarterly for Exercise and Sport
1990;61:146-153.

Numbers RL. Do-it-yourself the sectarian way. In: Risse
GB, Numbers RL, LeavittJW, editors. Medicine without
doctors: home health cure in American history. New
York: Science History Publications, 1977:49-72.

Olivova V. Scientific and professional gymnastics. In:
OlivovaV, editor. Sports andgames in theancient world.
New York: St. Martin's Press, 1985:135-145.

Paffenbarger RS Jr, Hyde RT, Wing AL, Lee IM, Jung DL,
Kampert JB. The association of changes in physical
activity level and other lifestyle characteristics with
mortality among men. New EnglandJournal ofMedicine
1993;328:538-545.

Park RJ. Athletes and their training in Britain and America,
1800-1914. In:BerrymanJW,ParkRJ,e(litors.Sportand
exercise science: essays in tile history of sports medicine.
[Jrbana, IL: Ilniversity of Illinois Press, 1992:57-107.

Park RJ. Measurement of pllysical jitness: a historical per-

spective. Office of Disease Prevention and Health Pro-
motion Monograph Series. Washington, DC: U.S.
Department of Health and Human Services, Public
Health Service, 1989: l-35.

Park RJ. The emergence of the academic discipline of
physical education in the United States. In: Brooks GA,
editor. Perspectives on,the academic discipline ofphysi-
cal education. Champaign, IL: Human Kinetics,
1981:2045.

Pate RR. A new definition of youth fitness. Physician and
Sportsmedicine 1983;11:77-83.
Pate RR, Pratt M, Blair SN, Haskell WL, Macera CA,
Bouchard C, et al. Physical activity and public health:
a recommendation from the Centers for Disease Con-
trol and Prevention and the American College of Sports
Medicine. Journal of the American Medical Association
1995;273:402-407.

Pollock ML. The quantification of endurance training
programs. Exercise and Sport Sciences Reviews
1973;1:155-188.

Pomeroy WC, White PD. Coronary heart disease in former
football players. Journal of the American Medical Asso-
ciation 1958;167:711-714.

Powell KE, Thompson PD, Caspersen CJ, Kendrick JS.
Physical activity and the incidence of coronary heart
disease. Annual Review ofPublic Health 1987;8:253-287.
Precope J. Hippocrates on diet and hygiene. London: Wil-
liams, Lea, and Company, 1952.
President's Council on Physical Fitness. Adult physical
fitness: aprogramfor men and women. Washington, DC:
U.S. Government Printing Office, 1965.
Progress of physical education. AmericanJournal of Edu-
cation 1826;1:19-23.

Ramazzini B. Diseases of workers [ 17131. Translated by
W.C. Wright. New York: Hafner, 1964.
ReindellH, Roskamm H,GerschlerW. Das inrervalltraining:
physiologischeGrundlagen,prah~ischeAnwendungen und
Schadigungsmiiglichheiten. Miinchen: Bath, 1962.
Reiser SJ. Responsibility for personal health: a historical
perspective. Journal of Medicine and Philosophy
1985;10:7-17.

Richardson MT, Leon AS, Jacobs DR, Ainsworth BE,
Serfass R. Ability of the Caltrac@ accelerometer to
assess daily physical activity levels.Joumal ofcardiop-
ulmonary Rehabilitation 1995;15:107-113.

Ricketson S. Means of preserving health and preventing
diseases. New York: Collins, Perkins, and Company,
1806.

Robinson S, Harmon PM. The lactic acid mechanism and
certain properties of the blood in relation to training.
AmericanJowrnaI of Physiology 1941;132:757-769.

54


~~~~~~~ F, Juneau M, Taylor CB, Haskell WL, Kraemer HC,
Ahn DK, et al. Assessment by a microprocessor of
adherence to home-based moderate-intensity exercise
training in healthy, sedentary middle-aged men and
\\omen. AmcricanJoumal ofcardiology 1987;60:71-75.

Rogers FB. Shadrach Ricketson (1768-1839): Quaker
bvgicnist. journal of the History of Medicine
I965;LO: 140-150.

Rogers JE. How has the depression in education affected
physical education? Journal o/ Health and Physical
Etjrlcntion f934;5: 12-3, 57-58.

I~,,,,k A. An investigation into the longevity of Cambridge
qrtsmcn. British MedicalJournal 1954;4:773-777.

\;iIIis JF, Buono MJ, Roby JJ, Carlson D, Nelson JA. The
<:.iltrac@ accelerometer as a physical activity monitor
for school-age children. Medicine and Science in Sports
td Excrcisc 1990;22:698-703.

s;rlli~ JF, Condon SA, Goggin KJ, Roby JJ, Kolody B,
..\Ic;iraz JE. The development ofself-administered physi-
c;il activity surveys for 4th grade students. Research
~,)r~(~rtcrfy~or Exercise and Sport 1993;64:25-31.

\.1111\ JF, Patrick K. Physical activity guidelines for adoles-
ccrits: consensus statement. Pediatric Exercise Science
I +)t;6:302-3 14.

\( Ii;irling EA. Versuche uber die Quantitat der, von einem
\lcnscbcn in 24 Stunden ausgeathmeten, Kohlensaure.
..\t~t~&t~ dcr Chemie und Pharmacie 1843;45:214-242.

~~licicitlcr EC, Ring GC. The influence of a moderate
.~mc)unt of physical training on the respiratory ex-
~.Ii:tngc and breathing during physical exercise. Ameri-
( ~rt~Jc~imul o~Physiology 1929;91:103-114.
`cs.11 KR. Gutin B, Presta E, Wang J, Van Itallie TB.
Ii~timation of human body composition by electrical
impcdancc methods: a comparative study. Journal o/
.+J'ficd Physiology 1985;58: 1565-1571.
`Ii.11111"' MA, Kyle RA. Nei Ching-oldest known medical
I,(~ok. Mayo Clinic Proceedings 1989;64:134.
`Ii<,.1 [il. In memoriam: Thomas K. Cureton, Jr.JournaI of
%?sicc~l Education, Recreation, and Dance 1993;64: 15.
`iLou()Ifi SF. Cullinane EM, Carleton RA, Thompson PD.
cisscssin VQL max in epidemiologic studies: modifica-
tion of the Astrand-Ryhming test. Medicine and Science
rri jJmIS and Exercise 1982;14:335-338.
"c'r~tl(~lfi SF, Lasater TM, Snow RC, Carleton RA. Self-
reported physical activity compared with maximal
"xygen uptake. Americ& Jouinal of Epidemiology
I985:122:101-105.

Historical Background, Terminology, Evolution of Recommendations, and Measurement

Sidney S, Haskell WL, Crow R, Sternfeld B, Oberman A,
Armstrong MA, et al. Symptom-limited graded tread-
mill exercise testing in young adults in the CARDIA
study. Medicine and Science in Sports and Exercise
1992;24:177-183.

Sinasalo UV, Juurtola T. Comparative study of the physi-
ological effects of two ski-training methods. Research
Quarterly 1957;28:288-294.

Skinner JS, Benson H, McDonough JR, Hames CG. Social
status, physical activity, and coronary proneness.Jour-
nal of Chronic Diseases 1966;19:773-783.
Sloan AW, Keen EN. Physical fitness of oarsmen and
rugby players before and after training. Journal of
Applied Physiology 1959;14:635-636.
Smith E. The influence of the labour of the tread-wheel
over respiration and pulsation, and its relation to the
waste of the system, and the dietary of the prisoners.
Medical Times and Gazette 1857;14:601-603.
Smith G. Prescribing the rules of health: self-help and
advice in the late eighteenth century. In: Porter R,
editor. Patients and practitioners: lay perceptions of
medicine in pre-industriaI society. Cambridge: Cam-
bridge University Press, 1985:249-282.
Snook GA. The history of sports medicine. Part 1. Ameri-
canJournal of Sports Medicine 1984;12:252-254.
Speck K. Ueber den Einfluss der Muskelthatigkeit auf
dem Athemprocess. Deutsche Archiv fur Klinische
Medicin 1889;45:461-528.

Spelman CC, Pate RR, Macera CA, Ward DS. Self-selected
exercise intensity of habitual walkers. Medicine and
Science in Sports and Exercise 1993;25: 1174-l 179.
Spirduso WW. Reaction and movement time as a function
of age and physical activity level. Journal of Gerontol-
ogy 1975;30:435-440.

Steinhaus AH. Health and physical fitness from the stand-
point of the physiologist. Journal of Health, Physical
Education, and Recreation 1936;7:224-227, 286-289.
Steinhaus AH, Bauer WW: Hellerbrandt FA, Kranz L,
Miller A. The role of exercise in physical fitness.
Journal of Health, Physical Education, and Recreation
1943;14:299-300,345.

Storey TA. The influence of fatigue upon the speed of
voluntary contraction of human muscle. American
Journal of Physiology 1903;8:355-375.

55


Physical Activity and Health

Taylor CB, Kraemer HC, Bragg DA, Miles LE, Rule B,
Savin WM. et al. A new system for long-term recording
and processing of heart rate and physical activity in
outpatients. Computers and Biomedical Research
1982;15:7-17.

Taylor HL, Anderson JT, Keys A. Physical activity, serum
cholesterol and other lipids in man. Proceedings ofthe
Society for Experimcncal Biology and Medicine
1957;95:383-388.

Taylor HL, Jacobs DR, Schucker B, Knudsen J, Leon AS,
Debacker G. A questionnaire for the assessment of
leisure-time physical activities.jowrnal ofchronic Dis-
eases 1978;31:741-755.

Tse SK, Bailey DM. T'ai chi and postural control in the
well elderly. Americanjournal ofoccupational Therapy
1992;46:295-300.

U.S. Department OfAgriculture, U.S. Department ofHealth
and Human Services. Nutrition and your health: dietary
guidelinesjor Americans. 4th ed. Washington, DC: U.S.
Department of Agriculture, 1995. Home and Garden
Bulletin No. 232.

U.S. Department of Health and Human Services. Healthy
peopIe2000: midcourse review and 1995 revisions. Wash-
ington, DC: U.S. Department of Health and Human
Services, Public Health Service, 1995.

U.S. Department of Health and Human Services. Healthy
people 2000: national health promotion and disease pre-
vention objectives,full report, with commentary. Wash-
ington, DC: U.S. Department of Health and Human
Services, Public Health Service, 1990. DHHS Publica-
tion No. (PHS)91-50212.

U.S. Department of Health and Human Services. The
Surgeon General's report on nutrition and health. Wash-
ington, DC: U.S. Department of Health and Human
Services, Public Health Service, 1988. DHHS Publica-
tion No. (PHS)88-50210.

U.S. Preventive Services Task Force. Guide CO clinical
preventive services. Baltimore: Williams and Wilkins,
1989.

U.S. Preventive Services Task Force. Guide CO clinical
preventive services. 2nd ed. Baltimore: Williams and
Wilkins, 1996.

Van Dalen DB, Bennett BL. A world history of physical
education: cultural, philosophical, comparative.
Englewood Cliffs, NJ: Prentice-Hall, 1971.

Verbrugge MH. Healthy animals and civic life: Sylvester
Graham's physiology of subsistence. Reviews in Ameri-
can History 1981;9:359-364.

Voorrips LE, Ravelli AC, Dongelmans PCA, Deurenberg
P, Van Staveren WA. A physical activity questionnaire
for the elderly. Medicine and Science in Sports and
Exercise 1991;23:974-979.

Warner JH. The therapeutic perspective: medical practice,
knowledge, and identity in America, 1820-1885. Cam-
bridge, MA: Harvard University Press, 1986.

Washburn RA, Adams LL, Haile GT. Physical activity
assessment for epidemiologic research: the utility of
two simplified approaches. Preventive Medicine
1987;16:636-646.

Washburn RA, Janney CA, Fenster JR. The validity of
objective physical activity monitoring in older indi-
viduals. Research Quarterly' for Exercise and Sport
1990;61:114-117.

Washburn RA, Smith KW, Jette AM, Janney CA. The
Physical Activity Scale for the Elderly (PASE): devel-
opment and evaluation. Journal o/Clinical Epidcmiol-
ogy 1993;46:153-162.

Wesley J. Primitive physic: or, an easy and natural method
o/curing most diseases [ 17471. Reprint, Philadelphia:
Parry Hall, 1793.

Westerterp KR, Brouns F, Saris WHM, ten Hoor F. Com-
parison of doubly labeled water with respirometry at
low- and high-activity levels. journal ofApplied Physi-
ology 1988;65:53-56.

Whorton JC. Crusadersforfitness: the history ofAmerican
health reformers. Princeton, NJ: Princeton University
Press, 1982.

Willich AFM. Lectures on diet and regimen. New York: T.
and J. Swords, 1801.

Wilmore JH, Behnke AR. An anthropometric estimation
of body density and lean body weight in young women.
American Journal of Clinical Nutrition 1970;23:267-
274.

Wilmore JH, Costill DL. Physiology ofsport and exercise.
Champaign, IL: Human Kinetics, 1994.

Wilson PWF, Paffenbarger RS, Morris JN, Havlik RJ.
Assessment methods for physical activity and physical
fitness in population studies: a report of an NHLBI
Workshop. American Heart Journal 1986;lll: 1177-
1192.

Wong TC, Webster JG, Montoye HJ, Washburn R. Por-
table accelerometer device for measuring human en-
ergy expenditure. IEEE Transactions on Biomedical
Engineering 1981;28:467-471.

56


Historical Background, Terminology, Evolution of Recommendations, and Measurement

~.,k~,v\ev sN. Kalcdin SV. Krasnova AF, Leshkevich LG.
Pclpov;t NK. Rogozkin VA, et al. Physiological and
chcmic;tf adaptation to muscular activity in relation to
k.t,~th of rest periods between exertions during train-
,n$. j~cllolov-Pkysiofogical Journal of the USSR
\~tlt ;$7:56-59.

Zukel WJ, Lewis RH, Enterline PE, Painter RC, Ralston
LS, Fawcett RM, et al. A short-term community study
of the epidemiology of coronary heart disease: a pre-
hminary report on the North Dakota study. American
Journal of Public Health 1959;49: 1630-1639.

57


               CHAPTER 3
PHYSIOLOGIC RESPONSES AND LONG-TERM
       ADAPTATIONS TO EXERCISE

Contents

111trocluction . .`_ . . . . . . . . _ . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  61

I`ll\,\iologic Responses to Episodes of Exercise  ....................................  61
<:ardiovascular and Respiratory Systems  ......................................  61
  Cardiovascular Responses to Exercise  .......................................  62
    CardiacOutput  .....................................................  62

     BloodFlow  ........................................................  63

     Blood Pressure  ......................................................  63

    Oxygen Extraction  ..................................................  63
    Coronary Circulation  ................................................  63

   Respiratory Responses to Exercise  .........................................  64

    Resistance Exercise  ....................................................  65

  skclctal Muscle  ..........................................................  65
hkcictd Muscle Energy Metabolism  ..........................................  65
   Energy Systems  .......................................................  65

    McrabolicRate  ........................................................  66
   Maximal Oxygen Uptake  ................................................  66

   LactateThreshold ......................................................  66
t IlJrmonal Responses to Exercise  ............................................  66
Immune Responses to Exercise  ..............................................  67

1 i)tlg-Terrn Adaptations to Exercise Training  .....................................  67
:\daptations of Skeletal Muscle and Bone  ......................................  67
Jletaholic Adaptations  .....................................................  69
Cardiovascular and Respiratory Adaptations  ...................................  71
  Long-Term Cardiovascular Adaptations  ....................................  71
  Respiratory Adaptations  .................................................  71


Physical Activity and Health

Contents, continued

Maintenance, Detraining, and Prolonged Inactivity  ................................  7 1
Maintaining Fitness and Muscular Strength  ....................................  72
Detraining  ..............................................................  72
Prolonged Inactivity  ......................................................  72

Special Considerations  .......................................................  73
Disability  ........................................................ . ......  73

Environmental Conditions  .................................................  73
EffectsofAge  ............................................................  75
DifferencesbySex  ........................................................  76

Conclusions  ...............................................................  77

Research Needs  ........ . .................................................  77

References . . . . . . . . . . . . . . ..__...................._............._............  77

60


              CHAPTER 3
PHYSIOLOGIC RESPONSES AND LONG-TERM
       ADAPTATIONS TO EXERCISE

Introduction

W hen challenged with any physical task, the
  human body responds through a series of
integrated changes in function that involve most, if
not all, of its physiologic systems. Movement re-
quires activation and control of the musculoskeletal
system; the cardiovascular and respiratory systems
provide the ability to sustain this movement over
extended periods. When the body engages in exer-
cise training several times a week or more frequently,
each of these physiologic systems undergoes specific
adaptations that increase the body's efficiency and
capacity. The magnitude of these changes depends
largely on the intensity and duration of the training
sessions, the force or load used in training, and the
body's initial level of fitness. Removal of the train-
ing stimulus, however, will result in loss of the
efficiency and capacity that was gained through
these training-induced adaptations; this loss is a
process called detraining.

This chapter provides an overview of how the
body responds to an episode of exercise and adapts
to exercise training and detraining. The discussion
focuses on aerobic or cardiorespiratory endurance
exercise (e.g., walking, jogging, running, cycling,
swimming, dancing, and in-line skating) and resis-
tance exercise (e.g., strength-developing exercises).
It does not address training for speed, agility, and
flexibility. In discussing the multiple effects of
exercise, this overview will orient the reader to the
physiologic basis for the relationship of physical
activity and health. Physiologic information perti-
nent to specific diseases is presented in the next
-chapter. For additional information, the reader is
referred to the selected textbooks shown in the
sidebar.

Selected Textbooks on Exercise Physiology
Astrand PO, Rodahl K. Texibook of work physiology.
3rd edition. New York: McGraw-Hill Book Company,
1986.

Brooks GA, Fahey TD, White TP. Exercise physiology:
human bioenergetics and its applications. 2nd edition.
Mountain View, CA: Mayfield Publishing Company,
1996.

Fox E, Bowers R, Foss M. The physiological basis for
exercise and sport. 5th edition. Madison, WI: Brown
and Benchmark, 1993.

McArdle WD, Katch FI, Katch VL. Essentials of
exercise physiology. Philadelphia, PA: Lea and
Febiger, 1994.

Powers SK, Howley ET. Exercise physiology: theory
and application tojitness and performance. Dubuque,
IA: William C. Brown, 1990.

Wilmore JH, Costill DL. Physiology of sport and
exercise. Champaign, IL: Human Kinetics, 1994.

Physiologic
of Exercise

Responses to Episodes

The body's physiologic responses to episodes of
aerobic and resistance exercise occur in the muscu-
loskeletal, cardiovascular, respiratory, endocrine,
and immune systems. These responses have been
studied in controlled laboratory settings, where ex-
ercise stress can be precisely regulated and physi-
ologic responses carefully observed.

Cardiovascular and Respiratory Systems
The primary functions of the cardiovascular and
respiratory systems are to provide the body with


Physical Activity and Health

oxygen (0,) and nutrients, to rid the body of carbon
dioxide (CO,) and metabolic waste products, to
maintain body temperature and acid-base balance,
and to transport hormones from the endocrine
glands to their target organs (Wilmore and Costill
1994). To be effective and efficient, the cardiovascu-
lar system should be able to respond to increased
skeletal muscle activity. Low rates of work, such as
walking at 4 kilometers per hour (2.5 miles per
hour), place relatively small demands on the cardio-
vascular and respiratory systems. However, as the
rate of muscular work increases, these two systems
will eventually reach their maximum capacities and
will no longer be able to meet the body's demands.

Cardiovascular Responses to Exercise
The cardiovascular system, composed of the heart,
blood vessels, and blood, responds predictably to
the increased demands of exercise. With few excep-
tions, the cardiovascular response to exercise is
directly proportional to the skeletal muscle oxygen
demands for any given rate of work, and oxygen
uptake (VOJ increases linearly with increasing rates
of work.

Cardiac Output

Cardiac output (Q) is the total volume of blood
pumped by the left ventricle of the heart per minute.
It is the product of heart rate (HR, number of beats
per minute) and stroke volume (SV, volume of blood
pumped per beat). The arterial-mixed venous oxygen
(A-TO,) difference is the difference between the oxy-
gen content of the arterial and mixed venous blood. A
person's maximum oxygen uptake NO, max) is a
function of cardiac output (Q) multiplied by the
A40,difference. Cardiac output thus plays an im-
portant role in meeting the oxygen demands for
work. As the rate of work increases, the cardiac
output increases in a nearly linear manner to meet
the increasing oxygen demand, but only up to the
point where it reaches its maximal capacity (Q max).
To visualize how cardiac output, heart rate, and
stroke volume change with increasing rates of work,
consider a person exercising on a cycle ergometer,
starting at 50 watts and increasing 50 watts every 2
minutes up to a maximal rate of work (Figure 3-l A,
B, and C). In this scenario, cardiac output and heart
rate increase over the entire range of work, whereas
stroke volume only increases up to approximately 40

Figure 3-1. Changes in cardiac output (A), heart rate
     (B), and stroke volume (C) with increasing
     rates of work on the cycle ergometer

(A)
221

6 t     I     I      I     I     I      I      I
25   50   75   100  125  150  175  200
          Power (watts)

(B)

200 1

X180-
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>160-
z
:140-
:120-
z
IlOO-

80 1     I      I     I     I      I      I      8
25   50   75   100  125  150  175  200
           Power (watts)

60-
25 50 75  100 125 150 175 200
           Power (watts)

62


Physiologic Responses and Long-Term Adaptations to Exercise

to 60 percent of the person's maximal oxygen uptake
(i'Oz max), after which it reaches a plateau. Recent
studies have suggested that stroke volume in highly
trained persons can continue to increase up to near
maximal rates of work (Scruggs et al. 1991; Gledhill,
Cox, Jamnik 1994).

Blood Flow

The pattern of blood flow changes dramatically when
a person goes from resting to exercising. At rest, the
skin and skeletal muscles receive about 20 percent of
the cardiac output. During exercise, more blood is
sent to the active skeletal muscles, and, as body
temperature increases, more blood is sent to the skin.
This process is accomplished both by the increase in
cardiac output and by the redistribution of blood flow
away from areas of low demand, such as the splanch-
nit organs. This process allows abou t 80 percent of the
cardiac output to go to active skeletal muscles and
skin at maximal rates of work (Rowe11 1986). With
exercise of longer duration, particularly in a hot and
humid environment, progressively more of the car-
diac output will be redistributed to the skin to counter
the increasing body temperature, thus limiting both
the amount going to skeletal muscle and the exercise
endurance (Rowe11 1986).

Blood Pressure

Mean arterial blood pressure increases in response to
dynamic exercise, largely owing to an increase in
systolic blood pressure, because diastolic blood pres-
sure remains at near-resting levels. Systolic blood
pressure increases linearly with increasing rates of
work, reaching peak values of between 200 and 240
millimeters of mercury in normotensive persons. Be-
cause mean arterial pressure is equal to cardiac output
times total peripheral resistance, the observed increase
in mean arterial pressure results from an increase in
cardiac output that outweighs a concomitant decrease
in total peripheral resistance. This increase in mean
arterial pressure is a normal and desirable response, the
result of a resetting of the arterial baroreflex to a higher
pressure. Without such a resetting, the body would
experience severe arterial hypotension during intense
activity (Rowe11 1993). Hypertensive patients typically
reach much higher systolic blood pressures for a given
rate of work, and they can also experience increases in
diastolic blood pressure. Thus, mean arterial pressure

is generally much higher in these patients, likely owing
to a lesser reduction in total peripheral resistance.
For the first 2 to 3 hours following exercise,
blood pressure drops below preexercise resting lev-
els, a phenomenon referred to as postexercise hy-
potension (Isea et al. 1994). The specific mechanisms
underlying this response have not been established.
The acute changes in blood pressure after an episode,
of exercise may be an important aspect of the role of
physical activity in helping control blood pressure in
hypertensive patients.

Oxygen Extraction

The A-TO, difference increases with increasing rates
of work (Figure 3-2) and results from increased
oxygen extraction from arterial blood as it passes
through exercising muscle. At rest, the A10, differ-
ence is approximately 4 to 5 ml of 0, for every 100 ml
of blood (ml/100 ml); as the rate of work approaches
maximal levels, the A-CO, difference reaches 15 to 16
ml/l00 ml of blood.

Coronary Circulation

The coronary arteries supply the myocardium with
blood and nutrients. The right and left coronary
arteries curve around the external surface of the heart,
then branch and penetrate the myocardial muscle
bed, dividing and subdividing like branches of a tree
to form a dense vascular and capillary network to
supply each myocardial muscle fiber. Generally one
capillary supplies each myocardial fiber in adult hu-
mans and animals; however, evidence suggests that
the capillary density of the ventricular myocardium
can be increased by endurance exercise training.

At rest and during exercise, myocardial oxygen
demand and coronary blood flow are closely linked.
This coupling is necessary because the myocardium
depends almost completely on aerobic metabolism
and therefore requires a constant oxygen supply.
Even at rest, the myocardium's oxygen use is high
relative to the blood flow. About 70 to 80 percent of
the oxygen is extracted from each unit of blood
crossing the myocardial capillaries; by comparison,
only about 25 percent is extracted from each unit
crossing skeletal muscle at rest. In the healthy heart,
a linear relationship exists between myocardial oxy-
gen demands, consumption, and coronary blood
flow, and adjustments are made on a beat-to-beat

63


Physical Activity and Health

Figure 3-2. Changes in arterial and mixed venous oxygen content with increasing rates of work on the
     cycle ergometer

18

A

arterial oxygen content

25

I         I
50      75

I
100

I         I         I         I         I         I       I
125     150     175     200     225     250     275

Power (watts)

basis. The three major determinants of myocardial
oxygen consumption are heart rate, myocardial
contractility, and wall stress (Marcus 1983;
Jorgensen et al. 1977). Acute increases in arterial
pressure increase left ventricular pressure and wall
stress. As a result, the rate of myocardial metabolism
increases, necessitating an increased coronary blood
flow. A very high correlation exists between both
myocardial oxygen consumption and coronary blood
flow and the product of heart rate and systolic blood
pressure (SBP) (Jorgensen et al. 1977). This so-
called double product (HR o SBP) is generally used
to estimate myocardial oxygen and coronary blood
flow requirements. During vigorous exercise, all
three major determinants of myocardial oxygen re-
quirements increase above their resting levels.

The increase in coronary blood flow during exer-
cise results from an increase in perfusion pressure of
the coronary artery and from coronary vasodilation.
`Most important, an increase in sympathetic nervous
system stimulation leads to an increase in circulating
catecholamines. This response triggers metabolic pro-
cesses that increase both perfusion pressure of the

64

coronary artery and coronary vasodilation to meet the
increased need for blood flow required by the increase
in myocardial oxygen use.

Respiratory Responses to Exercise

The respiratory system also responds when chal-
lenged with the stress of exercise. Pulmonary ven-
tilation increases almost immediately, largely
through stimulation, of the respiratory centers in
the brain stem from the motor cortex and through
feedback from the proprioceptors in the muscles
and joints of the active limbs. During prolonged
exercise, or at higher rates of work, increases in CO,
production, hydrogen ions (H'), and body and
blood temperatures stimulate further increases in
pulmonary ventilation. At low work intensities, the
increase in ventilation is mostly the result of in-
creases in tidal volume. At higher intensities, the
respiratory rate also increases. In normal-sized,
untrained adults, pulmonary ventilation rates can
vary from about 10 liters per minute at rest to more
than 100 liters per minute at maximal rates ofwork;
in large, highly trained male athletes, pulmonary


ventilation rates can reach more than 200 liters per
minute at maximal rates of work.

Resistance Exercise

The cardiovascular and respiratory responses to
episodes of resistance exercise are mostly similar to
those associated with endurance exercise. One no-
table exception is the exaggerated blood pressure
response that occurs during resistance exercise. Part
of this response can be explained by the fact that
resistance exercise usually involves muscle mass
that develops considerable force. Such high, isolated
force leads to compression of the smaller arteries and
results in substantial increases in total peripheral
resistance (Coyle 1991). Although high-intensity
resistance training poses a potential risk to hyperten-
sive patients and to those with cardiovascular dis-
ease, research data suggest that the risk is relatively
low (Gordon et al. 1995.) and that hypertensive
persons may benefit from resistance training (Tipton
1991; American College of Sports Medicine 1993).

Skeletal Muscle

The primary purpose of the musculoskeletal system is
to define and move the body. To provide efficient and
effective force, muscle adapts to demands. In response
to demand, it changes its ability to extract oxygen,
choose energy sources, and rid itself of waste prod-
ucts. The body contains three types of muscle tissue:
skeletal (voluntary) muscle, cardiac muscle or myo-
cardium, and smooth (autonomic) muscle. This sec-
tion focuses solely on skeletal muscle.

Skeletal muscle is composed of two basic types of
muscle fibers distinguished by their speed of con-
traction-slow-twitch and fast-twitch-a character-
istic that is largely dictated by different forms of the
enzyme myosin adenosinetriphosphatase (ATPase).
Slow-twitch fibers, which have relatively slow con-
tractile speed, have high oxidative capacity and fa-
tigue resistance, low glycolytic capacity, relatively
high blood flow capacity, high capiilary density, and
high mitochondrial content (Terjung 1995). Fast-
twitch muscle fibers have fast contractile speed and
are classified into two subtypes, fast-twitch type "a"
(FT,) and fast-twitch type "b" (FT,). FT, fibers have
moderately high oxidative capacity, are relatively
fatigue resistant, and have high glycolytic capacity,
relatively high blood flow capacity, high capillary

Physiologic Responses and Long-Term Adaptations to Exercise

, density, and high mitochondrial content (Terjung
1995). FT, fibers have low oxidative capacity, low
fatigue resistance, high glycolytic capacity, and fast
contractile speed. Further, they have relatively low
blood flow capacity, capillary density, and mito-
chondrial content (Terjung 1995).
There is a direct relationship between predomi-
nant fiber type and performance in certain sports.
For example, in most marathon runners, slow-twitch
fibers account for up to or more than 90 percent of
the total fibers in the leg muscles. On the other hand,
the leg muscles in sprinters are often more than 80
percent composed of fast-twitch fibers. Although the
issue is not totally resolved, muscle fiber type ap-
pears to be genetically determined; researchers have
shown that several years of either high-intensity
sprint training or high-intensity endurance training
do not significantly alter the percentage of the two
major types of fibers (folesz and Sreter 1981).

Skeletal Muscle Energy Metabolism
Metabolic processes are responsible for generating
adenosine triphosphate (ATP), the body's energy
source for all muscle action. ATP is generated by three
basic energy systems: the ATP-phosphocreatine
(ATP-PCr) system, the glycolytic system, and the
oxidative system. Each system contributes to energy
production in nearly every type of exercise. The
relative contribution of each will depend on factors
such as the intensity of work rate at the onset of
exercise and the availability of oxygen in the muscle.

Energy Systems

The ATP-PCr system provides energy from the ATP
stored in all of the body's cells. PCr, also found in all
cells, is a high-energy phosphate molecule that stores
energy. As ATP concentrations in the cell are reduced
by the breakdown of ATP to adenosine diphosphate
(ADP) to release energy for muscle contraction, PCr is
broken down to release both energy and a phosphate
to allow reconstitution of ATP from ADP. This process
describes the primary energy system for short, high-
intensity exercise, such as a 40- to 200-meter sprint;
during such exercise, the system can produce energy
at very high rates, and ATP and PCr stores, which are
depleted in lo-20 seconds, will last just long enough
to complete the exercise.

65


Physical Activity and Health

At high rates of work, the active muscle cells
oxygen demand exceeds its supply. The cell must
then rely on the glycolytic energy system to produce
ATP in the absence of oxygen (i.e., anaerobically).
This system can only use glucose, available in the
blood plasma and stored in both muscle and the liver as
glycogen. The glycolytic energy system is the primary
energy system for all-out bouts of exercise lasting
from 30 seconds to 2 minutes, such as an 800-meter
run. The major limitation of this energy system is
that it produces lactate, which lowers the pH of both
the muscle and blood. Once the pH drops below a
value of 6.4 to 6.6, enzymes critical for producing
energy are no longer able to function, and ATP
production stops (Wilmore and Costill 1994).
The oxidative' energy system uses oxygen to
produce ATP within the mitochondria, which are
special cell organelles within muscle. This process
cannot generate ATP at a high enough rate to sustain
an all-out sprint, but it is highly effective at lower
rates of work (e.g., long distance running). ATP can
also be produced from fat and protein metabolism
through the oxidative energy system. Typically, car-
bohydrate and fat provide most of the ATP; under
most conditions, protein contributes only 5 to 10
percent at rest and during exercise.

Metabolic Rate

The rate at which the body uses energy is known as
the metabolic rate. When measured while a person is
at rest, the resulting value represents the lowest (i.e.,
basal) rate of energy expenditure necessary to main-
tain basic body functions. Resting metabolic rate is
measured under highly controlled resting condi-
tions following a 12-hour fast and a good night's
sleep (Turley, McBride, Wilmore 1993). To quantify
the rate of energy expenditure during exercise, the
metabolic rate at rest is defined as 1 metabolic
equivalent (MET); a 4 MET activity thus represents
an activity that requires four times the resting meta-
bolic rate. The use of METS to quantify physical
activity intensity is the basis of the absolute intensity
scale. (See Chapter 2 for further information.)

Maximal Oxygen Uptake

During exercise,\iO, increases in direct proportion to
the rate of work. The point at which a person's 30, is
no longer able to increase is defined as the maximal

oxygen uptake (\iO,max) (Figure 3-3). A person's
VO,max is in part genetically determined; it can be
increased through training until the point that the
genetically possible maximum is reached.\iO,max is
considered the best estimate of a person's cardio-
respiratory fitness or aerobic power (Jorgensen et al.
1977).

f acta te Threshold
Lactate is the primary by-product of the anaerobic
glycolytic energy system. At lower exercise intensi-
ties, when the cardiorespiratory system can meet the
oxygen demands of active muscles, blood lactate
levels remain close to those observed at rest, because
some lactate is used aerobically by muscle and is
removed as fast as it enters the blood from the
muscle. As the intensity of exercise is increased,
however, the rate of lactate entry into the blood from
muscle eventually exceeds its rate of removal from
the blood, and blood lactate concentrations increase
above resting levels. From this point on, lactate
levels continue to increase as the rate of work in-
creases, until the point of exhaustion. The point at
which the concentration of lactate in the blood
begins to increase above resting levels is referred to
as the lactate threshold (Figure 3-3).
Lactate threshold is an important marker for endur-
ance performance, because distance runners set their
race pace at or slightly above the lactate threshold
(Farrell et al. 1979). Further, the lactate thresholds
of highly trained endurance athletes occur at a much
higher percentage of their VO,max, and thus at higher
relative workloads, than do the thresholds of un-
trained persons. This key difference is what allows
endurance athletes to perform at a faster pace.

Hormonal Responses to Exercise
The endocrine system, like the nervous system,
integrates physiologic responses and plays an im-
portant role in maintaining homeostatic conditions
at rest and during exercise. This system controls the
release of hormones from specialized glands through-
out the body, and these hormones exert their actions
on targeted organs and cells. In response to an
episode of exercise, many hormones, such as cat-
echolamines, are secreted at an increased rate, though
insulin is secreted at a decreased rate (Table 3-l).
The actions of some of these hormones, as well as

66


Physiologic Responses and Long-Term Adaptations to Exercise

Figure 3-3. Changes in oxygen uptake and blood lactate concentrations with increasing rates of work on the
     cycle ergometer*

  55



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Ti
2

30



25

VO,max
t

                      oxygen uptake (00, max) are indicated.

I        I        I        I        I        I        I        I        I

50

75

100

                         t
125    150    175    200    225    250    275
  Power (watts)

25

their specific responses to exercise, are discussed in
more detail in Chapter 4.

Immune Responses to Exercise
The immune system is a complex adaptive system
that provides surveillance against foreign proteins,
viruses, and bacteria by using the unique functions of
cells produced by the bone marrow and the thymus
gland. By interacting with neural and endocrine
factors, the immune system influences the body's
overall response to exercise (Reichlin 1992). A grow-
ing body of literature indicates that the incidence of
some infections may be influenced by the exercise
history of the individual (Nieman 1994; Hoffman-
Goetz and Pedersen 1994).

  Moderate exercise has been shotin to bolster the
function of certain components of the human immune
system- such as natural killer cells, circulatingl- and
B-lymphocytes, and cells of the monocyte-macroph-
age system -thereby possibly decreasing the inci-
dence of some infections (Keast, Cameron, Morton
1988; Pedersen and Ullum 1994; Woods and Davis
1994) and perhaps of certain types of cancer (Shephard
and Shek 1995).

Exercise of high intensity and long duration or
exercise that involves excessive training may have
adverse effects on immune function. In general, a
high-intensity, single episode of exercise results in a
marked decline in the functioning of all major cells of
the immune system (Newsholme and Parry-Billings
1994; Shephard and Shek 1995). In addition, over-
training may reduce the response of T-lymphocytes to
mutagenic stimulation, decrease antibody synthesis
and plasma level of immunogiobins and complement,
and impair macrophage phagocytosis. The reduced
plasma glutamine levels that occur with high-intensity
exercise or excessive training are postulated to con-
tribute to these adverse effects on the immune system
(Newsholme and Parry-Billings 1994).

Long-Term Adaptations to
Exercise Training

Adaptations of Skeletal Muscle and Bone
Skeletal muscle adapts to endurance training chiefly
through a small increase in the cross-sectional area
of slow-twitch fibers, because low- to moderate-

67


Physical Activity and Health

Table 3-1. A summary of hormonal changes during an episode of exercise

Hormone

Exercise
resoonse  Soecial relationshios         Probable imoortance

Catecholamines

Growth hormone (GH)

Adrenocorticotropic
hormone (ACTH)-cortisol

Thyroid-stimulating
hormone (TSH)-thyroxine

Luteinizing hormone (LH)

Testosterone

Estradiol-progesterone

Insulin

Glucagon

Renin-angiotensin-
aldosterone

Antidiuretic hormone
(ADI-

Parathormone
(PTH)-calcitonin

Erythropoietin

Prostaglandins

Increases  Greater increase with intense
     exercise; norepinephrine >
     epinephrine; increases less after
     training

Increases  Increases more in untrained
     persons; declines faster in trained
       persons

Increases  Greater increase with intense
      exercise; increases less
     after training with
      submaximal exercise

Increases  Increased thyroxine turnover
     with training but no toxic effects
      are evident

No change None
increases   None

Increases  Increases during luteal phase
     of the menstrual cycle

Decreases  Decreases less after training

Increases  Increases less after training

Increases  Same increase after training
       in rats

Expected   None
increase

Unknown None

Unknown None

May    May increase in response to
increase  sustained isometric contractions;
     may need ischemic stress

Increased blood glucose;
increased skeletal muscle and
liver glycogenolysis; increased
lipolysis

Unknown

Increased gluconeogenesis in
liver; increased mobilization of
fatty acids

Unknown

None

Unknown

Unknown

Decreased stimulus to use blood
glucose
Increased blood glucose via
glycogenolysis and
gluconeogenesis
Sodium retention to maintain
plasma volume

Water retention to maintain
plasma volume
Needed to establish proper
bone development
Would be important to increase
erythropoiesis
May be local vasodilators

Adapted from Wilmore JH, Costill DL. Physiplogy of sport and exercise. Champaign, IL: Human Kinetics, 1994, p. 136.

68


Physiologic Responses and Long-Term Adaptations to Exercise

intensity aerobic activity primarily recruits these
fibers (Abernethy, Thayer, Taylor 1990). Prolonged
endurance training (i.e., months to years) can lead to
a transition of FT, fibers to FTa fibers, which have a
higher oxidative capacity (Abernethy, Thayer, Taylor
1990). No substantive evidence indicates that fast-
twitch fibers will convert to slow-twitch fibers under
normal training conditions (lolesz and Sreter 1981).
Endurance training also increases the number of
capillaries in trained skeletal muscle, thereby allow-
ing a greater capacity for blood flow in the active
muscle (Terjung 1995).

  Resistance-trained skeletal muscle exerts con-
siderably more force because ofboth increased muscle
size (hypertrophy) and increased muscle fiber re-
cruitment. Fiber hypertrophy is the result of in-
creases in both the size and number of myofibrils in
both fast-twitch and slow-twitch muscle fibers
(Kannus et al. 1992). Hyperplasia, or increased fiber
number, has been reported in animal studies, where
the number of individual muscle fibers can be counted
(Gonyea et al. 1986), and has been indirectly demon-
strated during autopsies on humans by using direct
fiber counts to compare dominant and nondominant
paired muscles (Sjostrom et al. 1991).
During both aerobic and resistance exercise,
active muscles can undergo changes that lead to
muscle soreness. Some soreness is felt immediately
after exercise, and some can even occur during exer-
cise. This muscle soreness is generally not physically
limiting and dissipates rapidly. A more limiting sore-
ness, however, may occur 24 to 48 hours following
exercise. This delayed-onset muscle soreness is pri-
marily associated with eccentric-type muscle action,
during which the muscle exerts force while lengthen-
ing, as can happen when a person runs down a steep
hill or lowers a weight from a fully flexed to a fully
extended position (e.g., the two-arm curl). Delayed-
onset muscle soreness is the result of structural dam-
age to the muscle; in its most severe form, this damage
may include rupture of the cell membrane and disrup-
tion of the contractile elements of individual muscle
fibers (Armstrong, Warren, Warren 1991). Such dam-
age appears to result in an inflammatory response
(MacIntyre, Reid, McKenzie 1995).
Total inactivity results in,muscle atrophy and
loss of bone mineral and mass. Persons who are
sedentary generally have less bone mass than those
who exercise. but the increases in bone mineral and

mass that result from either endurance or resistance
training are relatively small (Chesnut 1993). The
role of resistance training in increasing or maintain-
ing bone mass is not well characterized. Endurance
training has little demonstrated positive effect on
bone mineral and mass. Nonetheless, even small
increases in bone mass gained from endurance or
resistance training can help prevent or delay the
process of osteoporosis (Drinkwater 1994). (See
Chapter 4 for further information on the effects of
exercise on bone.)

Themusculoskeletalsystemcannotfunctionwith-
out connective tissue linking bones to bones (liga-
ments) and muscles to bones (tendons). Extensive
animal studies indicate that ligaments and tendons
become stronger with prolonged and high-intensity
exercise. This effect is the result of an increase in the
strength of insertion sites between ligaments, ten-
dons, and bones, as well as an increase in the cross-
sectional areas of ligaments and tendons. These
structures also become weaker and smaller with sev-
eral weeks of immobilization (Tipton andvailas 1990),
which can have important implications for muscu-
loskeletal performance and risk of injury.

Metabolic Adaptations

Significant metabolic adaptations occur in skeletal
muscle in response to endurance training. First, both
the size and number of mitochondria increase sub-
stantially, as does the activity of oxidative enzymes.
Myoglobin content in the muscle can also be aug-
mented, increasing the amount of oxygen stored in
individual muscle fibers (Hickson 1981), but this
effect is variable (Svedenhag, Henriksson, Sylven
1983). Such adaptations, combined with the increase
in capillaries and muscle blood flow in the trained
muscles (noted in a previous section), greatly enhance
the oxidative capacity of the endurance-trained muscle.

Endurance training also increases the capacity of
skeletal muscle to store glycogen (Kiens et al. 1993).
The ability of trained muscles to use fat as an energy
source is also improved, and this greater reliance on
fat spares glycogen stores (Kiens et al. 1993). The
increased capacity to use fat following endurance
training results from an enhanced ability to mobilize
free-fatty acids from fat depots and an improved
capacity to oxidize fat consequent to the increase in
the muscle enzymes responsible for fat oxidation
(Wilmore and Costill 1994).

69


Physical Activity and Health

These changes in muscle and in cardiorespi-
ratory function are responsible for increases in
both \iO,max and lactate threshold. The endurance-
trained person can thus perform at considerably higher
rates of work than the untrained person. Increases in
30,max generally range from 15 to 20 percent follow-
ing a 6-month training period (Wilmore and Costill
1994). However, individual variations in this response
are considerable. In one study of 60- to 71-year-old
men and women who endurance trained for 9 to 12
months, the improvement in 30,max varied from 0
to 43 percent; the mean increase was 24 percent

(Kohrt et al. 1991). This variation in response may
be due in part to genetic factors and to initial levels
of fitness. To illustrate the changes that can be
expected with endurance training, a hypothetical
sedentary man's pretraining values have been com-
pared with his values after a 6-month period of
endurance training and with the values of a typical
elite endurance runner (Table 3-2).

Responses to endurance training are similar for
men and women. At all ages, women and men show
similar gains in strength from resistance training

(Rogers and Evans 1993; Holloway and Baechle 1990)

Table 3-2.  A hypothetical example of alterations in selected physiological variables consequent to a C-month
    endurance training program in a previously sedentary man compared with those of a typical elite
       endurance runner

Sedentary man

Variable              Pretraining

Posttraining

Runner

Cardiovascular
HR at rest (beats o min-`1
HR max (beats o min-`1
SV rest (ml)

SV max (ml)

Q rest (L o min.`)
Q max (L o min.`)
Heart volume (ml)
Blood volume (L)
Systolic BP rest (mmHg)
Systolic BP max (mmHg)
Diastolic BP rest (mmHg)
Diastolic BP max (mmHg)

71                   59                36
185                  183                 174
65                  80                125
120                   140                200
4.6                   4.7                4.5
22.2                 25.6               32.5
750                  820            1,200
4.7                  5.1                 6.0
135                  130                120
210                  205                210
78                  76                 65
82                   80                 65

Respiratory
vE rest (L o min.`)
V, rest (L o min-`1
TV rest (L)
TV max (L)
RR rest (breaths o min-`1
RR max (breaths o min-`1

Metabolic
A-CO, diff rest (ml o 100 ml-`)
A-CO, diff max (ml o 100 ml-`)
i.`O, rest (ml o kg-' o min-`1
90, max (ml o kg-' o min-`1
Blood lactate rest (mmol o L-7
Blood lactate max (mmol o L-`)

7                    6                  6
110                  135                195
0.5                  0.5               0.5
2.75                 3.0                3.9
14                   12                 12
40                  45                50



6.0                  6.0                6.0
34.5                 15.0               16.0
3.5                  3.5                3.5
40.5                 49.8               76.5
1 .o                  1 .o                1 .o

7.5

8.5

9.0

Adapted from Wilmore JH, Costill DL. Physiology ofsport and exercise. Champaign, IL: Human Kinetics, 1994, p. 230.
HR = heart rate; max = maximal; SV = stroke volume; 0 = cardiac output; BP = blood pressure;i/, = ventilatory volume; TV = tidal volume;
RR = respiration rate; A-60, diff = arterial-mixed venous oxygen difference;\jO, = oxygen consumption.

70


and similar gains in \iO,max from aerobic'endurance
training (Kohrt et al. 1991; Mitchell et al. 1992).

Cardiovascular and Respiratory Adaptations
Endurance training leads to significant cardiovascu-
lar and respiratory changes at rest and during steady-
state exercise at both submaximal and maximal rates
of work. The magnitude of these adaptations largely
depends on the person's initial fitness level; on mode,
intensity, duration, and frequency of exercise; and
on the length of training (e.g., weeks, months, years).

Long-Term Cardiovascular Adaptations
Cardiac output at rest and during submaximal exer-
cise is essentially unchanged following an endur-
ance training program. At or near maximal rates of
work, however, cardiac output is increased sub-
stantially, up to 30 percent or more (Saltin and
Rowe11 1980). There are important differences in
the responses of stroke volume and heart rate to
training. After training, stroke volume is increased
at rest, during submaximal exercise, and during
maximal exercise; conversely, posttraining heart
rate is decreased at rest and during submaximal
exercise and is usually unchanged at maximal rates
of work. The increase in stroke volume appears to
be the dominant change and explains most of the
changes observed in cardiac output.
  Several factors contribute to the increase in
stroke volume from endurance training. Endurance
training increases plasma volume by approximately
the same percentage that it increases stroke volume
(Green, Jones, Painter 1990). An increased plasma
volume increases the volume of blood available to
return to the right heart and, subsequently, to the
left ventricle. There is also an increase in the end-
diastolic volume (the volume of blood in the heart
at the end of the diastolic filling period) because of
increased amount of blood and increased return of
blood to the ventricle during exercise (Seals et al.
1994). This acute increase in, the'left ventricle's
end-diastolic volume stretches its walls, resulting
in a more elastic recoil.

Endurance training also results in long-term
changes in the structure of the heart that augment
stroke volume. Short-term adaptive responses in-
clude ventricular dilatation; this increase in the vol-
ume of the ventricles allows end-diastolic volume to

Physiologic Responses and Long-Term Adaptations to Exercise

increase without excessive stress on the ventricular
walls. Long-term adaptive responses include hyper-
trophy of the cardiac muscle fibers (i.e., increases in
the size of each fiber). This hypertrophy increases
the muscle mass of the ventricles, permitting greater
force to be exerted with each beat of the heart.
Increases in the thickness of the posterior and septal
walls of the left ventricle can lead to a more forceful
contraction of the left ventricle, thus emptying more
of the blood from the left ventricle (George, Wolfe,
Burggraf 1991).

Endurance training increases the number of cap-
illaries in trained skeletal muscle, thereby allowing a
greater capacity for blood flow in the active muscle
(Terjung 1995). This enhanced capacity for blood
flow is associated with a reduction in total peripheral
resistance; thus, the left ventricle can exert a more
forceful contraction against a lower resistance to
flow out of the ventricle (Blomqvist and Saltin 1983).
Arterial blood pressure at rest, blood pressure
during submaximal exercise, and peak blood pres-
sure all show a slight decline as a result of endurance
training in normotensive individuals (Fagard and
Tipton 1994). However, decreases are greater in
persons with high blood pressure. After endurance
training, resting blood pressure (systolic/diastolic)
will decrease on average -3/-3 mmHg in persons with
normal blood pressure; in borderline hypertensive
persons, the decrease will be -6/-7 mmHg; and in
hypertensive persons, the decrease will be -lo/-8
mmHg (Fagard and Tipton 1994). (See Chapter 4 for
further information.)

Respiratory Adaptations

The major changes in the respiratory system from en-
durance training are an increase in the maximal rate of
pulmonary ventilation, which is the result of increases
in both tidal volume and respiration rate, and an
increase in pulmonary diffusion at maximal rates of
work, primarily due to increases in pulmonary blood
flow, particularly to the upper regions of the lung.

Maintenance, Detraining, and
Prolonged Inactivity
Most adaptations that result from both endurance
and resistance training will be reversed if a person
stops or reduces training. The greatest deterioration

71


Physical Activity and Health

in physiologic function occurs during prolonged bed
rest and immobilization by casts. A basic mainte-
nance training program is necessary to prevent these
losses in function.

Maintaining Fitness and Muscular Strength
Muscle strength and cardiorespiratory capacity are
dependent on separate aspects of exercise. After a per-
son has obtained gains in VO,max by performing
cardiorespiratory exercise six times per week, two
to four times per week.is the optimal frequency of
training to maintain those gains (Hickson and
Rosenkoetter 1981). Further, a substantial part of
the gain can be retained when the duration of each
session is reduced by as much as two-thirds, but
only if the intensity during these abbreviated ses-
sions is maintained at 270 percent of VO,max
(Hickson et al. 1985). If training intensity is reduced
by as little as one-third, however, a substantial
reduction in \iO,max can be expected over the next
15 weeks (Hickson et al. 1985).
In previously untrained persons, gains in mus-
cular strength can be sustained by as little as a single
session per week of resistance training, but only if
the intensity is not reduced (Graves et al. 1988).

Detraining

With complete cessation of exercise training, a sig-
nificant reduction in iTO,max and a decrease in
plasma volume occur within 2 weeks; all prior func-
tional gains are dissipated within 2 to 8 months, even
if routine low- to moderate-intensity physical activ-
ity has taken the place of training (Shephard 1994).
Muscular strength and power are reduced at a much
slower rate than \iO,max, particularly during the
first few months after an athlete discontinues resis-
tance training (Fleck and Kraemer 1987). In fact, no
decrement in either strength or power may occur for
the first 4 to 6 weeks after training ends (Neufer et al.
1987). After 12 months, almost half of the strength
gained might still be retained if the athlete remains
moderately active (Wilmore and Costil! 1994).

Prolonged Inactivity

The effects of prolonged inactivity have been studied
by placing healthy young male athletes and sedentary
volunteers in bed for up to 3 weeks after a control
period during which baseline measurements were

made. The'resulting detrimental changes in physi-
ologic function and performance are similar to those
resulting from reduced gravitational forces during
space flight and are more dramatic than those result-
ing from detraining studies in which routine daily
activities in the upright position (e.g., walking, stair
climbing, lifting, and carrying) are not restricted.
Results of bed rest studies show numerous physi-
ologic changes, such as profound decrements in
cardiorespiratory function proportional to the dura-
tion of bed rest (Shephard 1994; Saltin et al. 1968).
Metabolic disturbances evident within a few days of
bed rest include reversible glucose intolerance and
hyperinsulinemia in response to a standard glucose
load, reflecting cell insulin resistance (Lipman et al.
1972); reduced total energy expenditure; negative
nitrogen balance, reflecting loss of muscle protein;
and negative calcium balance, reflecting loss of bone
mass (Bloomfield and Coyle 1993). There is also a
substantial decrease in plasma volume, which affects
aerobic power.

From one study, a decline in VO,max of 15 per-
cent was evident within 10 days of bed rest and
progressed to 27 percent in 3 weeks; the rate of loss was
approximately 0.8 percent per day of bed rest
(Bloomfieldand Coyle 1993). The decrement inVO,max
from bed rest and reduced activity results from a
decrease in maximal cardiac output, consequent to a
reduced stroke volume. This, in turn, reflects the
decrease in end-diastolic volume resulting from a
reduction in total blood and plasma volume, and
probably also from a decrease in myocardial contrac-
tility (Bloomfield and Coyle 1993). Maximal heart
rate and A-TO, difference remain unchanged
(Bloomfield and Coyle 1993). Resting heart rate
remains essentially unchanged or is slightly in-
creased, whereas resting stroke volume and cardiac
output remain unchanged or are slightly decreased.
However, the heart rate for submaximal exertion is
generally increased to compensate for the sizable
reduction in stroke volume.

Physical inactivity associated with bed rest or
prolonged weightlessness also results in a progres-
sive decrement in skeletal muscle mass (disuse
atrophy) and strength, as well as an associated
reduction in bone mineral density that is approxi-
mately proportional to the duration of immobiliza-
tion or weightlessness (Bloomfield and Coyle 1993).
The loss of muscle mass is not as great as that which

77


Physiologic Responses and Long-Term Adaptations to Exercise

~,c~~~rs \vith immobilization of a limb by a plaster
ilaSt. but it exceeds that associated with cessation of
rcsist;lnce exercise training. The muscle groups
n,05t affected by prolonged immobilization are the
.,ntlgravity postural muscles of the lower extremi-
t,cs (Bloomfield and Coyle 1993). The loss of nor-
m&,1 mechanical strain patterns from contraction of
,hcsc muscles results in a corresponding loss of
Llcllsit\ in the bones of the lower extremity, particu-
1.~~1~ the heel and the spine (Bloomfield and Coyle
IQQJ). Muscles atrophy faster than bones lose their
Llcn%ity. For example, 1 month of bed rest by healthy
VoIIII$ men resulted in a 10 to 20 percent decrease
,,, Inl~sclc fiber cross-sectional areaand a 21 percent
, L~d~~ction in peak isokinetic torque of knee exten-
sc,~~ (Bloomfield and Coyle 1993), whereas a simi-
I,\r period of bed rest resulted in a reduction in bone
InlncraI density of only 0.3 to 3 percent for the
I~lmhar spine and 1.5 percent for the heel.
c!Llantitative histologic examination of muscle
I,lc,ljsics of the vastus lateralis of the leg following
~~llmobilization shows reduced cross-sectional area
1,)~ hot11 slow-twitch and fast-twitch fibers, actual
~~c~.rolic` changes in affected fibers., loss of capillary
clwsily. and a decline in aerobic enzyme activity,
L I MI Ininc phosphate, and glycogen stores (Bloomfield
.IIKI (:oylc 1993). On resuming normal activity,
I c.\,cr\il,iliry of these decrements in cardiorespiratory,
In~*r.tholic. and muscle function is fairly rapid (within
~I.I\.\ to weeks) (Bloomfield and Coyle 1993). By
h ~~IILI'A~~, the reversal of the decrement of bone min-
~.KII clcnsity requires weeks to months.

Special Considerations

111~ l~hysiologic responses to exercise and physi-
olo::ic adaptations to training and detraining, re-
\ I~.\\uI in the preceding sections, can be influenced
!I\ J Ill~ml~cr of factors, including physical disability,
~`ll\`lronmcntal conditions, age, and sex.

Disability

.\l~ll~~ugh there is a paucity of information about
Ptl!~~i~~logic responses to exercise among persons
`A Ith disabilities, existing information supports the
:l~ill~ln that the capacity of these persons to adapt to
"`( rcascd levels of physical activity is similar to that
"I I'crsons without disabilities. Many of the acute

effects of physical activity on the cardiovascular,
respiratory, endocrine, and musculoskeletal systems
have been demonstrated to be similar among persons
with disabilities, depending on the specific nature of
the disability. For example, physiologic responses to
exercise have been studied among persons with
paraplegia (Davis 1993), quadriplegia (Figoni 1993),
mental retardation (Fernhall 1993), multiple sclero-
sis (Ponichtera-Mulcare 1993), and postpolio syn-
drome (Birk 1993).

Environmental Conditions

The basic physiologic respbnses to an episode of
exercise vary considerably with changes in environ-
mental conditions. As environmental temperature
and humidity increase, the body is challenged to
maintain its core temperature. Generally, as the
body's core temperature increases during exercise,
blood vessels in the skin begin to dilate, diverting
more blood to the body's surface, where body heat
can be passed on to the environment (unless envi-
ronmental temperature exceeds body temperature).
Evaporation of water from the skin's surface signifi-
cantly aids in heat loss; however, as humidity in-
creases, evaporation becomes limited.
These methods for cooling can compromise car-
diovascular function during exercise. Increasing
blood flow to the skin creates competition with the
active muscles for a large percentage of the cardiac
output. When a person is exercising for prolonged
periods in the heat, stroke volume will generally
decline over time consequent to dehydration and
increased blood flow in the skin (Rowe11 1993;
Montain and Coyle 1992). Heart rate increases sub-
stantially to try to maintain cardiac output to com-
pensate for the reduced stroke volume.
High air temperature is not the only factor that
stresses the body's ability to cool itself in the heat.
High humidity, low air velocity, and the radiant heat
from the sun and reflective surfaces also contribute
to the total effect. For example, exercising under
conditions of 32oC (90oF) air temperature, 20 per-
cent relative humidity, 3.0 kilometers per hour (4.8
miles per hour) air velocity, and cloud cover is much
more comfortable and less stressful to the body than
the same exercise under conditions of 24oC (75oF)
air temperature, 90 percent relative humidity, no air
movement, and direct exposure to the sun.

73


Physical Activity and Health

Children respond differently to heat than adults
do. Children have a higher body surface area to body
mass ratio (surface area/mass), which facilitates heat
loss when environmental temperatures are below
skin temperature. When environmental tempera-
ture exceeds skin temperature, children are at an
even greater disadvantage because these mecha-
nisms then become avenues of heat gain. Children
also have a lower rate of sweat production; even
though they have more heat-activated sweat glands,
each gland produces considerably less sweat than
that of an adult (Bar-Or 1983).
The inability to maintain core temperature can
lead to heat-related injuries. Heat cramps, character-
ized by severe cramping of the active skeletal muscles,
is the least severe of three primary heat disorders.
Heat exhaustion results when the demand for blood
exceeds what is available, leading to competition for
the body's limited blood supply. Heat exhaustion is
accompanied by symptoms including extreme fa-
tigue, breathlessness, dizziness, vomiting, fainting,
cold and clammy or hot and dry skin, hypotension,
and a weak, rapid pulse (Wilmore and Costill 1994).
Heatstroke, the most extreme of the three heat disor-
ders, is characterized by a core temperature of 40oC
(104oF) or higher, cessation of sweating, hot and dry
skin, rapid pulse and respiration, hypertension, and
confusion or unconsciousness. If left untreated, heat-
stroke can lead to coma, then death. People experi-
encing symptoms of heat-related injury should be
taken to a shady area, cooled with by whatever means
available, and if conscious given nonalcoholic bever-
ages to drink. Medical assistance should be sought.
To reduce the risk of developing heat disorders, a
person should drink enough fluid to try to match
that which is lost through sweating, avoid extreme
heat, and reduce the intensity of activity in hot
weather. Because children are less resistant to the
adverse effects of heat during exercise, special atten-
tion should be given to protect them when they
exercise in the heat and to provide them with'extra
fluids to drink.

Stresses associated with exercising in the ex-
treme cold are generally less severe. For most situa-
tions, the problems associated with cold stress can be
eliminated by adequate clothing. Still, cold stress can
induce a number of changes in the physiologic re-
sponse to exercise (Doubt 1991; Jacobs, Martineau,

Vallerand 1994; Shephard 1993). These include the
increased generation of body heat by vigorous activ-
ity and shivering, increased production of catechola-
mines, vasoconstriction in both the cutaneous and
nonactive skeletal muscle beds to provide insulation
for the body's core, increased lactate production, and
a higher oxygen uptake for the same work (Doubt
1991). For the same absolute temperature, exposure
to cold water is substantially more stressful than
exposure to cold air because the heat transfer in
water is about 25 times greater than in air (Toner and
McArdle 1988). Because the ratio of surface area to
mass is higher in children than in adults, children
lose heat at a faster rate when exposed to the same
cold stress. The elderly tend to have a reduced
response of generating body heat and are thus more
susceptible to cold stress.

Altitude also affects the body's physiologic re-
sponses to exercise. As altitude increases, barometric
pressure decreases, and the partial pressure of inhaled
oxygen is decreased proportionally. A decreased par-
tial pressure of oxygen reduces the driving force to
unload oxygen from the air to the blood and from the
blood to the muscle, thereby compromising oxygen
delivery (Fulco and Cymerman 1988). VO,max is
significantly reduced at altitudes greater than 1,500
meters. This effect impairs the performance of endur-
ance activities. The body makes both short-term and
long-term adaptations to altitude exposure that en-
able it to at least partially adapt to this imposed stress.
Because oxygen delivery is the primary concern, the
initial adaptation that occurs within the first 24 hours
of exposure to altitude is an increased cardiac output
both at rest and during submaximal exercise. Ventila-
tory volumes are also increased. An ensuing reduction
in plasma volume increases the concentration of red
blood cells (hemoconcentration), thus providing more
oxygen molecules per unit of blood (Grover, Weil,
Reeves 1986). Over several weeks, the red blood cell
mass is increased through stimulation of the bone
marrow by the hormone erythropoietin.
Exercising vigorously outdoors when air qual-
ity is poor can also produce adverse physiologic
responses. In addition to decreased tolerance for
exercise, direct respiratory effects include increased
airway reactivity and potential exposure to harmful
vapors and airborne dusts, toxins, and pollens
(Wilmore and Costill 1994).

74


Physiologic Responses and Long-Term Adaptations to Exercise

Effects of Age

When absolute values are scaled to account for
differences in body size, most differences in physi-
ologic function between children and adults dis-
appear. The exceptions are notable. For the same
absolute rate of work on a cycle ergometer, chil-
dren will have approximately the same metabolic
cost, orVO,demands, but they meet those demands
differently. Because children have smaller hearts,
their stroke volume is lower than that for adults for
the same rate of work. Heart rate is increased to
compensate for the lower stroke volume; but be-
cause this increase is generally inadequate, cardiac
output is slightly lower (Bar-Or 1983). The A-GO,
difference is therefore increased to compensate for
the lower cardiac output to achieve the sameV0,.
The iTO,max, expressed in liters per minute, in-
creases during the ages of 6-18 years for boys and
6-14 years for girls (Figure 3-4) before it reaches a
plateau (Krahenbuhl, Skinner, Kohrt 1985). When
expressed relative to body weight (milliliters per
kilogram per minute),VO,max remains fairly stable
for boys from 6-18 years of age but decreases

steadily for girls during those years (Figure 3-4)
(Krahenbuhl, Skinner, Kohrt 1985). Most likely,
different patterns of physical activity contribute to
this variation because the difference in aerobic
capacity between elite female endurance athletes
and elite male endurance athletes is substantially
less than the difference between boys and girls in
general (e.g., 10 percent vs. 25 percent) (Wilmore
and Costill 1994).

The deterioration of physiologic function with
aging is almost identical to the change in function
that generally accompanies inactivity. Maximal heart
rate and maximal stroke volume are decreased in
older adults; maximal cardiac output is thus de-
creased, which results in a VO,max lower than that
of a young adult (Raven and Mitchell 1980). The
decline inVOzmax approximates 0.40 to 0.50 milli-
liters per kilogram per minute per year in men,
according to data from cross-sectional studies; this
rate of decline is less in women (Buskirk and
Hodgson 1987). Through training, both older men
and women can increase their30,max values by
approximately the same percentage as those seen

Figure 3-4. Changes in CiO, max with increasing age from 6 to 18 years of age in boys and girls*

4.0 1

r 60

E 3.5
.-
E
p 3.0
al
.=
=
2 2.5
m
FL
3 2.0
5
$
;: 1.5

-5
E  1.0
.-
::
2 0.5

60~s. ml/kg                -- c- 4

              II ."            @`-
H-50 t
    Girls, ml/kg ,R'               x.

                         .                 3

       /-- 0'                 40 ;
          HH

  *CM- --- -0-- @@(Boys, L/min          2
                                          30 =
                              _--- __---______      -D
ed c-            ---- -7-c                         G
                                                            k

             c- /-- o-            _---     Girls, I h-tin
   /j/A- /----- -cc-

s--- -- &Z--

1     ?D
20 zj
     -
$

`Values are expressed in both liters per minute and  t 10 g.
relative to body weight (milliliters Per kilogram PP~ minlltej

0.0 I       I       I       I       I       I       I       I       I       I       I       I   1 0
   6     7     8     9    IO    11    12    13    14    15    16    17    18
                     Age (years)

Data were taken from Krahenbuhl GS, Skinner IS, Kohrt WM 198S and Bar-Or 0 1983

75


Physical Activity and Health

in younger adults (Kohrt et al. 1991). The inter-
relationships of age, \i02max, and training status
are evident when the loss inVO,max with age is
compared for active and sedentary individuals
(Figure 3-5).

When the cardiorespiratory responses of an older
adult are coinpared with those of a young or middle-
aged adult at the same absolute submaximal rate of
work, stroke volume for an older person is generally
lower and heart rate is higher from the attempt to
maintain cardiac output. Because this attempt is
generally insufficient, the A-+0, difference must
increase to provide the same submaximal oxygen
uptake (Raven and Mitchell 1980; Thompson and
Dorsey 1986). Some researchers have shown, how-
ever, that cardiac output can be maintained at both
submaximal and maximal rates of work through a
higher stroke volume in older adults (Rodeheffer et
al. 1984).

The deterioration in physiological function nor-
mally associated with aging is, in fact, caused by a
combination of reduced physical activity and the

aging process itself. By maintaining an active
lifestyle, or by increasing levels of physical activ-
ity if previously sedentary, older persons can
maintain relatively high levels of cardiovascular
and metabolic function, including irO,max (Kohrt
et al. 199 1)) and of skeletal muscle function (Rogers
and Evans 1993). For example, Fiatarone and col-
leagues (1994) found an increase of 113 percent in
the strength of elderly men and women (mean age of
87.1 years) following a lo-week training program of
progressive resistance exercise. Cross-sectional thigh
muscle area was increased, as was stair-climbing
power, gait velocity, and level of spontaneous activ-
ity. Increasing endurance and strength in the elderly
contributes to their ability to live independently.

Differences by Sex

For the most part, women and men who participate
in exercise training have similar responses in car-
diovascular, respiratory, and metabolic function
(providing that size and activity level are normal-
iced). Relative increases in\jO,max are equivalent

Figure 3-5. Changes in 00, max with aging, comparing an active population and sedentary population (the
    figure also illustrates the expected increase in VO, max when a previously sedentary person begins
     an exercise program)

A-  Active adults

R&&on in
activity plus
weight gain

Sedentary adults

0 (              I              I              I
    20         30          40          50
                        Age (years)
Adapted, by permission, from Buskirk ER, Hodgson JL. Federation Proceedings 1987.

I              I              I
60          70          80

76


Physiologic Responses and Long-Term Adaptations to Exercise

for women and men (Kohrt et al. 1991; Mitchell et
al. 1992). Some evidence suggests that older women
accomplish this increase inVO,max mainly through
an increase in the AGO, difference, whereas younger
women and men have substantial increases in stroke
volume, which increases maximal cardiac output
(Spina et al. 1993). With resistance training, women
experience equivalent increases in strength (Rogers
and Evans 1993; Holloway and Baechle 1990),
although they gain less fat-free mass due to less
muscle hypertrophy.

  Several sex differences have been noted in the
acute response to exercise. At the same absolute
rate of exercise, women have a higher heart rate
response than men, primarily because of a lower
stroke volume. This lower stroke volume is a func-
tion of smaller heart size and smaller blood volume.
In addition, women have less potential to increase
the A-CO, difference because of lower hemoglobin
content. Those differences, in addition to greater
fat mass, result in a lower V02max in women, even
when normalized for size and level of training
(Lewis, Kamon, Hodgson 1986).

Conclusions

1. Physical activity has numerous beneficial physi-
ologic effects. Most widely appreciated are its
effects on the cardiovascular and musculo-
skeletal systems, but benefits on the functioning
of metabolic, endocrine, and immune systems
are also considerable.

2. Many of the beneficial effects of exercise train-
ing-from both endurance and resistance ac-
tivities-diminish within 2 weeks if physical
activity is substantially reduced, and effects
disappear within 2 to 8 months if physical
activity is not resumed.

3. People of all ages, both male and female, undergo
beneficial physiologic adaptations to physical
activity.

Research Needs
1. Explore individual variations in response to
exercise.

2.





3.







4.



5.

Better characterize mechanisms through which
the musculoskeletal system responds differen-
tially to endurance and resistance exercise.
Better characterize the mechanisms by which
physical activity reduces the risk of cardiovascular
disease, hypertension, and non-insulin-
dependent diabetes mellitus.
Determine the minimal and optimal amount of
exercise for disease prevention.

Better characterize beneficial activity profiles for
people with disabilities.

References

Abernethy PJ, Thayer R, Taylor AW. Acute and chronic
responses of skeletal muscle to endurance and sprint
exercise: a review. Sports Medicine 1990;10:365-389.

American College of Sports Medicine. Position stand:
physical activity, physical fitness, and hypertension.
Medicine and Science in Sports and Exercise 1993;25:i-x.
Armstrong RB, Warren GL, Warren JA. Mechanisms of
exercise-induced muscle fibre injury. Sports Medicine
1991;12:184-207.

Bar-Or 0. Pediatric sports medicine for the practitioner:
from physiologic principles to clinical applications. New
York: Springer-Verlag. 1983.

Birk TJ. Poliomyelitis and the post-polio syndrome: exer-
cise capacities and adaptations--current research, fu-
ture directions, and widespread applicability. Medicine
and Science in Sports and Exercise 1993;25:466-472.

Blomqvist CG, Saltin B. Cardiovascular adaptations to
physical training. Annual Review of Physiology
1983;45:169-189.

Bloomfield SA, Coyle EF. Bed rest, detraining, and reten-
tion of training-induced adaptation. In: Durstine JL,
King AC, Painter PL, Roitman JL, Zwiren LD, editors.
ACSM's resource manualfor guidelinesfor exercise test-
ing and prescription. 2nd ed. Philadelphia: Lea and
Febiger, 1993: 115-128.

Buskirk ER, Hodgson JL. Age and aerobic power: the rate
of change in men and women. Federation Proceedings
1987;46: 1824-1829.

Chesnut CH Ill. Bone mass and exercise. American journal
oJMedicine 1993;95(5A Suppl):34S-365.

77


Physical Activity and Health

Coyle EF. Cardiovascular function during exercise: neural
control factors. Sports Science Exchange 1991;4:1-6.

Davis GM. Exercise capacity of individuals with para-
plegia. Medicine and Science in Sports and Exercise
1993;25:423-432.

Doubt TJ. Physiology of exercise in the cold. Sports
Medicine 1991;11:367-381.

Drinkwater BL. Physical activity, fitness, and osteoporosis.
In: Bouchard C, Shephard RJ, Stephens T, editors.
Physical activity,fitness, and health: international proceed-
ings and consensus statement. Champaign, IL: Human
Kinetics, 1994:724-736.

Fagard RH, Tipton CM. Physical activity, fitness, and
hypertension. In: Bouchard C, Shephard RJ, Stephens T,
editors. Physical activily,fitness, and health: international
proceedings and consensus statement. Champaign, IL:
Human Kinetics, 1994:633-655.

Farrell PA, Wilmore JH, Coyle EF, Billing JE, Costill DL.
Plasma lactate accumulation and distance running
performance. Medicine and Science in Sports 1979;ll:
338-344.

Fernhall B. Physical fitness and exercise training of indi-
viduals with mental retardation. Medicine and Science
in Sports and Exercise 1993;25:442-450.

Fiatarone MA, O'Neill EF, Ryan ND, Clements KM, Solares
GR, Nelson ME, et al. Exercise training and nutritional
supplementation for physical frailty in very elderly
people. New England Journal of Medicine 1994;
330:1769-1775.

Figoni SF. Exercise responses and quadriplegia. Medicine
and Science in Sports and Exercise 1993;25:433-441.

Fleck SJ, Kraemer WJ. Designing resistance training pro-
grams. Champaign, IL: Human Kinetics, 1987:264.

Fulco CS, Cymerman A. Human performance and acute
hypoxia. In: Pandolf KB, Sawka MN, Gonzalez RR,
editors. Human performance physiology and environ-
mental medicine at terrestrial extremes. Indianapolis:
Benchmark Press, 1988:467-495.

George KP, Wolfe LA, Burggraf GW. The "athletic heart
syndrome": a critical review. Sports Medicine
1991;11:300-331.

Gledhill N, Cox D, Jamnik R. Endurance athletes' stroke
volume does not plateau: major advantage is diastolic
function. Medicine and Science in Sports and Exercise
1994;26:1116-1121.

Gonyea WJ, Sale DG, Gonyea FB, Mikesky A. Exercise-
induced increases in muscle fiber number. European
Journal of Applied Physiology 1986;55:137-141.

Gordon NF, Kohl HW III, Pollock ML, Vaandrager
H, Gibbons LW, Blair SN. Cardiovascular safety of
maximal strength testing in healthy adults. American
Journal of Cardiology 1995;76:851-853.

Graves JE, Pollock ML, Leggett SH, Braith RW, Carpenter
DM, Bishop LE. Effect of reduced training frequency
on muscular strength. lntemational Journal of Sports
Medicine 1988;9:316-319.

Green HJ, Jones LL, Painter DC. Effects of short-term
training on cardiac function during prolonged exer-
cise. Medicine and Science in Sports and Exercise
1990;22:488-493.

Grover RF, Weil JV, Reeves JT. C&diovascular adaptation
to exercise at high altitude. Exercise and Sport Sciences
Reviews 1986;14:269-302.

Hickson RC. Skeletal muscle cytochrome c and myoglo-
bin, endurance, and frequency of training. Journal of
Applied Physiology 1981;51:746-749.

Hickson RC, Foster C, Pollock ML, Galassi TM, Rich S.
Reduced training intensities and loss of aerobic power,
endurance, and cardiac growth. Journal of Applied
Physiology 1985;58:492-499.

Hickson RC, Rosenkoetter MA. Reduced training fre-
quencies and maintenance of increased aerobic power.
Medicine and Science in Sports and Exercise 1981;13:
13-16.

Hoffman-Goetz L, Pedersen BK. Exercise and the immune
system: a model of the stress response? Immunology
Today 1994;15:382-387.

Holloway JB, Baechle TR. Strength training for female
athletes: a review of selected aspects. Sports Medicine
1990;9:216-228.

Isea JE, Piepoli M, Adamopoulos S, Pannarale G, Sleight
P, Coats AJS. Time course of haemodynamic changes
after maximal exercise. European Journal of Clinical
Investigation 1994;24:824-829.
Jacobs I, Martineau L, Vallerand AL. Thermoregulatory
thermogenesis in humans during cold stress. Exercise
and Sport Sciences Reviews 1994;22:221-250.

Jolesz F, Sreter FA. Development, innervation, and activity-
pattern induced changes in skeletal muscle. Annual
Review of Physiology 1981;43:531-552.

Jorgensen CR, Gobel FL, Taylor HL, Wang Y. Myocardial
blood flow and oxygen consumption during exercise.
Annals offhe New York Academy of Sciences 1977;301:
213-223.

78


Physiologic Responses and Long-Term Adaptations to Exercise

Kannus P, Jozsa L, Renstrijm P, Jarvinen M, Kvist M,
Lehto M, et al. The effects of training, immobiliza-
tion, and remobilization on musculoskeletal tissue.
ScandinavianJournal of Medicine and Science in Sports
1992;2: 100-l 18.

Keast D, Cameron K, Morton AR. Exercise and the im-
mune response. Sports Medicine 1988;5:248-267.
Kiens B, Lessen-Gustavsson B, Christensen NJ, Saltin B.
Skeletalmusclesubstrate utilizationduringsubmaximal
exercise in man: effect of endurance training.]oumal of
Physiology 1993;469:459-478.

Kohrt WM, Malley MT, Coggan AR, Spina RJ, Ogawa T,
Ehsani AA, et al. Effects of gender, age, and fitness level
on response of VO, max to training in 60-71 yr olds.
Journal ofApplied Physiology 1991;71:2004-2011.

Krahenbuhl GS, Skinner JS, Kohrt WM. Developmental
aspects of maximal aerobic power in children. Exercise
and Sport Sciences Reviews 1985;13:503-538.
Lewis DA, Kamon E, Hodgson JL. Physiological differ-
ences between genders: implications for sports condi-
tioning. Sports Medicine 1986;3:357-369.

Lipman RL, Raskin P, Love T, Triebwasser J, Lecocq FR,
Schnure JJ. Glucose intolerancg during decreased
physical activity in man. Diabetes 1972;21:101-107.

Maclntyre DL, Reid WD, McKenzie DC. Delayed muscle
soreness: the inflammatory response to muscle injury
and its clinical implications. Sports Medicine 1995;20:
24-40.

Marcus ML. The coronary circulation in health and disease.
New York: McGraw Hill, 1983.

Mitchell JH, Tate C, Raven P, Cobb F, Kraus W, Moreadith
R, et al. Acute response and chronic adaptation to
exercise in women. Medicine and Science in Sports and
Exercise 1992;24(6 Suppl):S258-S265.

Montain SJ, Coyle EF. Influence of graded dehydration on
hyperthermia and cardiovascular drift during exercise.
Journal oJApplied Physiology 1992;73:1340-1350.

Neufer PD, Costill DL, Fielding R4, Flynn MG, Kirwan
JP. Effect of reduced training on muscular strength and
endurance in competitive swimmers. Medicine and
Science in Sports and Exercise 1987;19:486-490.

Newsholme EA, Parry-Billings M. Effects of exercise on the
immune system. In: Bouchard C, Shephard RJ, Stephens
T, editors. Physical activity,fitness, and health: intema-
tionaf proceedings and consensus statement. Champaign,
IL: Human Kinetics, 1994:451-455.

Nieman DC. Exercise, infection, and immunity. Intema-
tional Journal of Sports Medicine 1994;15(3 Suppl):
s131-s141.

Pedersen BK, Ullum H. NK cell response to physical
activity: possible mechanisms of action. Medicine and
Science in Sports and Exercise 1994;26:140-146.
Ponichtera-Mulcare JA. Exercise and multiple sclerosis.
Medicine and Science in Sports and Exercise 1993;25:
45 l-465.

Raven PB, Mitchell J. The effect of aging on the cardiovas-
cular response to dynamic and static exercise. In:
Weisfeldt ML, editor. The aging heart. New York:
Raven Press, 1980:269-256:

Reichlin S. Neuroendocrinology. In: Wilson JD, Foster
DW, editors. Williams' textbook of endocrinology. 8th
ed. Philadelphia: W.B. Saunders, 1992:201.

Rodeheffer RJ, Gerstenblith G, Becker LC, Fleg JL,
Weisfeldt ML, Lakatta EG. Exercise cardiac output
is maintained with advancing age in healthy human
subjects: cardiac dilatation and increased stroke
volume compensate for a diminished heart rate.
Circulation 1984;69:203-213.

Rogers MA, Evans WJ. Changes in skeletal muscle with
aging: effects of exercise training. Exercise and Sport
Sciences Reviews 1993;21:65-102.

Rowe11 LB. Human cardiovascular control. New York:
Oxford University Press, 1993.
Rowe11 LB. Human circulation regulation during physical
stress. New York: Oxford University Press, 1986.

SaltinB,Blomqvist G,MitchellJH,JohnsonRL,Wildenthal
K, Chapman CB. Response to exercise after bed rest
and after training: a longitudinal study of adaptive
changes in oxygen transport and body composition.
Circulation 1968;38(Suppl 7):1-78.

Saltin B, Rowell LB. Functional adaptations to physical
activity and inactivity. Federation Proceedings 1980;39:
1506-1513.

Scruggs KD, Martin NB, Broeder CE, Hofman Z, Thomas
EL, Wambsgans KC, et al. Stroke volume during
submaximal exercise in endurance-trained normo-
tensive subjects and in untrained hypertensive sub-
jects with beta blockade (propranolol and pindolol).
AmericanJournal ofCardiology 1991;67:416-421.

Seals DR. HagbergJM, Spina RJ, Rogers MA, Schechtman
KB, Ehsani AA. Enhanced left ventricular perfor-
mance in endurance trained older men. Circulation
1994:89:198-205.

79


Physical Activity and Health

Shephard RJ. Aerobic fitness and health. Champaign, IL:
Human Kinetics, 1994.

Shephard RJ. Metabolic adaptations to exercise in the
cold: an update. Sports Medicine 1993;16:266-289.

Shephard RJ, Shek PN. Cancer, immune function, and
physical activity. CanadianJournal ofApplied Physiology
1995;20: l-25.

Sjostrdm M, Lexell J, Eriksson A, Taylor CC. Evidence of
fibre hyperplasia in human skeletal muscles from
healthy young men? A left-right comparison of the
fibre number in whole anterior tibialis muscles. Euro-
peanJoumal o/Applied Physiology 1991;62:301-304.

Spina RJ, Ogawa T, Miller TR, Kohrt WM, Ehsani AA.
Effect of exercise training on left ventricular perfor-
mance in older women free of cardiopulmonary dis-
ease. AmericanJournal of Cardiology 1993;71:99-104.

Svedenhag J, Henriksson J, Sylven C. Dissociation of
training effects on skeletal muscle mitochondrial en-
zymes and myoglobin in man. Acta Physiologica
Scandinavica 1983;117:213-218.

Terjung RL. Muscle adaptations toaerobic training. Sports
Science Exchange 1995;B: l-4.

Thompson PD, Dorsey DL. The heart of the masters
athlete. In: Sutton JR, Brock RM, editors. Sports medi-
cine for the mature athlete. Indianapolis: Benchmark
Press, 1986:309-318.

Tipton CM. Exercise, training, and hypertension: an
update. Exercise and Sport Sciences Reviews 1991;19:
447-505.

Tipton CM, Vailas AC. Bone and connective tissue adap-
tations to physical activity. In: Bouchard C, Shephard
RJ, Stephens T, Sutton JR, McPherson BD, editors.
Exercise,fitness, and health: a consensus ofcurrent knowl-
edge. Champaign, IL: Human Kinetics, 1990:331-344.
Toner MM, McArdle WD. Physiological adjustments of
man to the cold. In: Pandolf KB, Sawka MN, Gonzalez
RR, editors. Human performance physiology and envi-
ronmental medicine at terrestrial extremes. Indianapolis:
Benchmark Press, 1988:361-399.

Turley KR, McBride PJ, Wilmore JH. Resting metabolic
rate measured after subjects spent the night at home vs
at a clinic. American Journal of Clinical Nutrition
1993;58:141-144.

Wilmore JH, Costill DL. Physiology of sport and exercise.
Champaign, IL: Human Kinetics, 1994.

Woods JA, Davis JM. Exercise, monocyte/macrophage
function, and cancer. Medicine and Science in Sports
and Exercise 1994;26:147-157.

80


             CHAPTER 4
THE EFFECTS OF PHYSICAL ACTIVITY ON
        HEALTH AND DISEASE

Contents

Introduction  .......................


Overall Mortality  ...................
Conclusions  .....................


Cardiovascular Diseases  ..............

. .

.

.

.....................................  85




.....................................  85

.....................................  87




.....................................  87

                                  . .
Cardiovascular Diseases Combined  ..........................................  87
Coronary Heart Disease  ...................................................  87

CVD Risk Factors in Children  ..............................................  91

Stroke   ................................................................ 102
HighBloodPressure  ......... . ............................................ 103
Biologic Plausibility  ...................................................... 110

Atherosclerosis  ........................................................ 110
Plasma Lipid/Lipoprotein Profile  .......................................... 111

BloodPressure   ........................................................ 111

lschemia  ............................................................. 111

Thrombosis  ........................................................... 112
Arrhythmia  ........................................................... 112

Conclusions  ............................................................ 112

Cancer  ................................................................... 112

Colorectal Cancer  ......................................................... 113

  Colon Cancer  ......................................................... 113

  RectalCancer  ......................................................... 116
Hormone-Dependent Cancers in Women  ..................................... 116

  BreastCancer  ......................................................... 117
  Other Hormone-Dependent Cancers in Women  .......................... 1 ... 120


Contents, continued

Cancers in Men . . . . . . . . .

Prostate Cancer . . . . . . .
Testicular Cancer . . . . .
Other Site-Specific Cancers
Biologic Plausibility . . . .
Conclusions . . _ . . . . . . . .

.......

.......

.......

.......

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

.............................. 121


.............................. 124


.............................. 124


..............................  124


.......................... . ... 124

Non-Insulin-Dependent Diabetes Melhtus  ...................................... 125
Physical Activity and NIDDM  .............................................. 125
Biologic Plausibility  ...................................................... 128

Conclusions  ............................................................ 129

Osteoarthritis  ............................................................. 129
Physical Activity in Persons with Arthritis ..................................... 129
Biologic Plausibility  ......................................................  130

Conclusions  ............... . ............................................ 130

Osteoporosis  .............................................................. 130
Biologic Plausibility  ...................................................... 13 1
Physical Activity and the Prevention of Fractures and Falling  .....................  132
Conclusions  ............................................................ 132

Obesity  .................................................................. 133
Physical Activity and Obesity  ............................................... 133
Biologic Plausibility  ...................................................... 134

Conclusions  ............................................................ 135

MentalHealth  ............................................................. 135
Physical Activity and Mental Health  ......................................... 136
Biologic Plausibility  ...................................................... 141

Conclusions  ............................................................. 141

Health-Related Quality of Life  ................................................ 141
Conclusions  ............................................................ 142


Contents, continued

Adverse Effects of Physical Activity  ............................................. 142
Types of Adverse Effects  .................................................... 142
  Musculoskeletal Injuries  .................................................. 142

  Metabolic Abnormalities .................................................. 143
  Hematologic and Body Organ Abnormalities  .................................. 143

  Hazards ........................................................ . .... ..14 3
  Infectious, Allergic, and Inflammatory Conditions  ............................. 143

  Cardiac Events  ......................................................... 143

Occurrence of Adverse Effects  ............................................... 144

Conclusions  ........................................................... ..14 4

Nature of the Activity/Health Relationship  ....................................... 144
Causality  ................................................................ 144
Population Burden of Sedentary Living  ........................................ 145

Dose  ................................................................... 146

Conclusions  ............................................................. 148

ChapterSummary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .._..... 149

Conclusions  ............................................................. ..14 9

ResearchNeeds  ........................................................... 150

References . . . . . . . . .._........................._............................ 151


             CHAPTER 4
THE EFFECTS OF PHYSICAL ACTIVITV ON
        HEALTH AND DISEASE

Introduction

T his chapter examines the relationship of physi-
cal activity and cardiorespiratory fitness to a
variety of health problems. The primary focus is on
diseases and conditions for which sufficient data exist
to evaluate an association with physical activity, the
strength of such relationships, and their potential
biologic mechanisms. Because most of the research to
date has addressed the health effects of endurance-
type physical activity (involving repetitive use of
large muscle groups, such as in walking and bicy-
cling), this chapter focuses on that type of activity.
Unless otherwise specified, the term physical activity
should be understood to refer to endurance-type
physical activity. Less well studied are the health
effects of resistance-type physical activity (i.e., that
which develops muscular strength); when this type
of physical activity is discussed, it is specified as
such. Much of the research summarized is based on
studies having only white men as participants; it
remains to be clarified whether the relationships
described here are the same for women, racial and
ethnic minority groups, and people with disabilities.
Physical activity is difficult to measure directly.
Three types of physical activity measures have been
used in observational studies over the last 40 years.
Most studies have relied on self-reported level of
physical activity, as recalled by people prompted by
a questionnaire or interview. A more objectively
measured characteristic is cardiorespiratory fitness
(also referred to as cardiorespiratory endurance)
which is measured by aerobic power (see Chapter 2
for more information on measurement issues). Some
studies have relied on occupation to classify people
according to how likely they were to be physically
active at work.

Epidemiologic studies of physical activity and
health have compared the activity levels of people
who have or develop diseases and those who do not.
Cohort studies follow populations forward in time to
observe how physical activity habits affect disease
occurrence or death. In case-control studies, groups
of persons who have disease and separate groups of
people who do not have disease are asked to recall
their previous physical activity. Cross-sectional stud-
ies assess the association between physical activity
and disease at the same point in time. Clinical trials,
on the other hand, attempt to alter physical activity
patterns and then assess whether disease occurrence
is modified as a result.

Results from epidemiologic studies can be used
to estimate the relative magnitude or strength of an
association between physical activity and a health
outcome. Two such measures used in this chapter
are risk ratio (RR) and odds ratio (OR). For these
measures, an estimate of 1 .O indicates no association,
when the risk of disease is equivalent in the two
groups being compared. RR or OR estimates greater
than 1.0 indicate an increase in risk; those less than
1.0 indicate a decreased risk. Confidence intervals
(CI) reported with estimates of association indicate
the precision of the estimate, as well as its statistical
significance. When the CI range includes 1.0, the
effect is considered likely to have occurred by chance;
therefore the estimate of association is not consid-
ered statistically significantly different from the null
value of 1.0.

Overall Mortality

Persons with moderate to high levels of physical
activity or cardiorespiratory fitness have a lower
mortality rate than those with sedentary habits or


Physical Activity and Health

low cardiorespiratory fitness. For example, com-
pared with people who are most active, sedentary
people experience between a 1.2-fold to a 2-fold
increased risk of dying during the follow-up interval
(Slattery and Jacobs 1988; Slattery, Jacobs, Nichaman
1989; Leon and Connett 1991; Stender et al. 1993;
Sandvik et al. 1993; Chang-Claude and Frentzel-
Beyme 1993; Kaplan et al. 1987; Arraiz, Wigle, Mao
1992; Paffenbarger et al. 1993).
Associations are generally stronger for measured
cardiorespiratory fitness than for reported physical
activity (Blair, Kohl, Paffenbarger 1989). Blair, Kohl,
and Barlow (1993) showed that low levels of cardio-
respiratory fitness were strongly associated with
overall mortality for both women (RR = 5.35; 95%
CI, 2.44-11.73) and men (RR= 3.16; 95% CI, 1.92-
5.20). The association with physical inactivity was
weaker for men (RR = 1.70; 95% CI, 1.06-2.74), and
there was no association for women (RR = 0.95; 95%
CI, 0.54-1.70).

Though cardiorespiratory fitness may be the
better indicator of regular physical activity, the level
of reported physical activity has been associated with
reduced all-cause mortality. Paffenbarger, Lee, and
Leung (1994) evaluated several types of recalled
activity (walking, stair climbing, all sports, moderate-
level sports, and total energy expended in activity per
week) as predictors of all-cause mortality among
male Harvard alumni. Among these men, the relative
risk of death within the follow-up period was reduced
to 0.67 with walking 15 or more kilometers per week
(reference group, < 5 kilometers/week), to 0.75 with
climbing 55 or more flights of stairs per week (refer-
ence group, < 20 flights/week), to 0.63 with involve-
ment in moderate -sports (reference group, no
involvement), and to 0.47 with 3 or more hours of
moderate sports activities per week (reference group,
< 1 hour/week). Most importantly, there was a signifi-
cant trend of decreasing risk of death across increas-
ing categories of distance walked, flights of stairs
climbed, and degree of intensity of sports play.
Researchers have also examined age.-specific ef-
fects of different levels of physical activity on all-
cause mortality. Kaplan and colleagues (1987) have
shown that physical activity level has an effect on
death rates among both older and younger persons.
Data from a study of 9,484 Seventh-Day Adventist
men aged 30 years or older in 1958 who were

followed through 1985 indicated that both moderate
and intense levels of activity reduced overall risk of
death even late in life (Lindsted, Tonstad, Kuzma
1991). Both moderate and vigorous levels of activity
were equally protective at age 50 years. The protec-
tive effect of high levels of activity lasted only until
age 70, but the protective effect for moderate activity
lasted beyond age 80.

The studies cited thus far in this section assessed
physical activity or cardiorespiratory fitness at
baseline only and then followed up for mortality. A
stronger test for a causal relationship is to examine
the effect that changing from lower to higher levels
of physical activity or cardiorespiratory fitness has
on subsequent mortality. Two large studies provide
such evidence. Among middle-aged Harvard male
alumni who were sedentary in 1962 or 1966, those
who took up moderately intense sports activity dur-
ing the study's 11 years of follow-up had a 23 percent
lower death rate (RR= 0.77; 95% CI, 0.58-0.96) than
those who remained sedentary (Paffenbarger et al.
1993). (By comparison, men who quit smoking
during the interval had a 41 percent decrease in
death rate [RR = 0.59; 95% CI, 0.43-0.801.) Men
45-84 years of age who took up moderately intense
sports extended their longevity on average by 0.72
years; added years of life were observed in all
age groups, including men 75-84 years of age
(Paffenbarger et al. 1993).

  Similar reductions in death rates with increases
in cardiorespiratory fitness were reported for men in
the Aerobics Center Longitudinal Study. Blair and
colleagues (1995) reported a reduction in death rates
among healthy men (aged 20-82 years) who im-
proved their initially low levels of cardiorespiratory
fitness. The men performed two maximal exercise
tests an average of 4.8 years apart; follow-up for
mortality after the second test occurred an average of
4.7 years later. Among men in the bottom fifth of the
cardiorespiratory fitness distribution, those who
improved to at least a moderate fitness level had a 44
percent lower death rate than their peers who re-
mained in the bottom fifth (RR = 0.56; 95% CI, 0.41-
0.75). After multivariate adjustment, those who
became fit had a significant 64 percent reduction in
their relative mortality rate. In comparison, men
who stopped smoking reduced their adjusted RR by
about 50 percent.

86


Conclusions

The data reviewed here suggest that regular physical
activity and higher cardiorespiratory fitness decrease
overall mortality rates in a dose-response fashion.
Whereas most studies of physical activity and health
address specific diseases and health conditions, the
studies in this chapter provide more insight into the
biologic mechanisms by which mortality rate reduc-
tion occurs.

Cardiovascular Diseases

Despite a progressive decline since the late 196Os,
cardiovascular diseases (CVDs), including coronary
heart disease (CHD) andstroke, remain major causes
of death, disability, and health care expenditures in
the United States (NCHS 1994; Gillum 1994). In
1992, more than 860,000 deaths in the United States
were attributed to heart disease and stroke (DHHS
1994). High blood pressure, a major risk factor for
CVD, affects about 50 million Americans (National
Institutes of Health [NIH] 1993), including an esti-
mated 2.8 million children and adolescents 6-17
years of age (Task Force on Blood Pressure Control
in Children 1987). The prevalence of CVD increases
with age and is higher among African Americans than
whites. The majority of population-based research in
the area of physical activity and health has focused on
some aspect of CVD.

Cardiovascular Diseases Combined
Most of the reported studies relating physical activity
to CVD have reported CVD mortality as an endpoint;
two also reported on nonfatal disease, and one re-
ported on CVD hospitalization (Table 4-l). Seven
cohort studies evaluated the association between
level of physical activity and the risk of total CVD
(Kannel and Sorlie 1979; Paffenbarger et al. 1984;
Kannel et al. 1986; Lindsted, Tonstad, Kuzma 1991;
Arraiz, Wigle, Mao 1992; Shermanet al. 1994; LaCroix
et al. 1996). All relied on a single point-in-time
estimate of physical activity, in some cases assessed
as long as 26 years before the end of the observational
period, and four had follow-up periods of 114 years.
Four of the seven studies found both an inverse
association and a dose-response gradient between
level of physical activity and risk of CVD outcome
(Kannel and Sorlie 1979; Paffenbarger et al. 1984;

Kannel et al. 1986; LaCroix et al. 1996). One study
among men found an inverse association among the
moderately active group but less of an effect in the
vigorously active group (Lindsted, Tonstad, Kuzma
199 1). One study of women 50-74 years of age found
no relationship of physical activity with CVD mor-
tality (Sherman et al. 1994).

Five large cohort studies have related cardiores-
piratory fitness to the risk of CVD mortality (Arraiz,
Wigle, Mao 1992; Ekelund et al. 1988; Blair, Kohl,
Paffenbarger 1989; Sandvik et al. 1993; Blair et al.
1995), but only one provided a separate analysis for
women (Blair, Kohl, Paffenbarger 1989). Each of
these studies demonstrated an inverse dose-response
relationship between level of cardiorespiratory fit-
ness and CVD mortality. Three of the five studies
relied on a maximal or near-maximal exercise test to
estimate cardiorespiratory fitness. One study (Blair
et al. 1995) demonstrated that men with low cardio-
respiratory fitness who became fit had a lower risk of
CVD mortality than men who remained unfit.
Taken together, these major cohort studies indi-
cate that low levels of physical activity or cardiores-
piratory fitness increase risk of CVD mortality.
Findings seem to be more consistent for studies of
cardiorespiratory fitness, perhaps because of its
greater precision of measurement, than for those of
reported physical activity. The demonstrated dose-
response relationship indicates that the benefit de-
rived from physical activity occurs at moderate levels
of physical activity or cardiorespiratory fitness and
increases with increasing levels of physical activity
or higher levels of fitness.

Coronary Heart Disease

Numerous studies have examined the relationship
between physical activity and CHD as a specific CVD
outcome. Reviews of the epidemiologic literature
(Powell et al. 1987; Berlin and Colditz 1990; Blair
1994) have concluded that physical activity is strongly
and inversely related to CHD risk. Although physical
exertion may transiently increase the risk of an acute
coronary event among persons with advanced coro-
nary atherosclerosis, particularly among those who
do not exercise regularly (Mittleman et al. 1993;
Willich et al. 1993; Siscovick et al. 1984), physically
active people have a substantially lower overall risk
for major coronary events.

The Effects of Physical Activity on Health and Disease

87


Physical Activity and Health

Table 4-1. Population-based studies of association of physical activity or cardiorespiratory fitness with total
      cardiovascular diseases

Study
Physical activity
Kannel and
Sorlie (1979)

Paffenbarger et al.
(1984)

Kannel et al.
(1986)

Lindsted, Tonstad,
Kuzma
(1991)

Arraiz, Wigle,
Mao (1992)

Sherman et al
(1994)

LaCroix et al.
(1996)

Population

Definition of physical activity     Definition of
or cardiorespiratory fitness       cardiovascular disease

1,909 Framingham (MA)
men and 2,311 women
aged 35-64 years at
14-year follow-up

16,936 US male college
alumni who entered
college between 1916
and 1950; followed
from 1962-l 978

1 ,166 Framingham (MA)
men aged 45-64 years;
24-year follow-up

9,484 Seventh-Day
Adventist men aged
2 30 years; 26-year
follow-up

Stratified probability
sample of Canadians
aged 30-69 years,
conducted in 1978-
1979; 7-year follow-up

1,404 Framingham (MA)
women aged 50-74
years; 16-year
follow-up

1,645 HMO members
age 2 65 years; 4.2-year
average follow-up

Cardiorespiratory fitness
Ekelund et al.     3,106 North American
(1988)        men aged 30-69
          years; 8.5-year
          average follow-up

Blair et al.
(1989)

10,244 men and 3,120
women aged 2 20 years;
8.1 -year average
follow-up

Physical activity index based
on hours per day spent at
activity-specific intensity

Physical activity index estimated
from reports of stairs climbed,
city blocks walked, and sports
played each week

Physical activity index based on
hours per day at activity-specific
intensity; occupational physical
activity classified by physical
demand of work

Self-report to single physical
activity question

Physical activity index
summarizing frequency, intensity,
and duration of leisure-time
activity and household chores

Physical activity index based on
hours per day spent at activity-
specific intensity

Hours of walking per week

Submaximal aerobic capacity
estimated from exercise test

Maximal aerobic capacity
estimated by exercise test

CVD fatal and nonfatal
in men (n = 140 deaths,
n = 435 total cases) and
women (n = 101 deaths)

Death due to CVD
(n = 640)

Death due to CVD
(n = 325)

Death due to CVD
(ICD-8 41 O-458)
(n = 410)

Death due to CVD
(n = 256)

CVD incidence (n = 994)
and mortality (n = 303)

CVD hospitalization
(ICD-9 390-448)
(n = 359)

Death due to CVD
(KID-8 390-458)
(n = 45)

Death due to CVD
(ICD-9 390-448)
in men (n = 66)
and women (n = 7)

88


The Effects of Physical Activity on Health and Disease

Main findings

Dose     Adjustment for confounders
resDonse*    and other comments

Inverse association between physical activity
index and CVD mortality for both men
and women

Inverse association; relative to highest
category (2,000+ kcal/week), relative risk
estimates were 1.28 and 1.84, respectively

Inverse association; for physical activity
index, age-adjusted RR relative to high
activity category = 1.62 for low activity,
I .30 for moderate; for occupational activity,
age-adjusted RR relative to heavy physical
demand category = 1.34 for sedentary, 1.26
for light, 1.09 for medium

Inverse association relative to inactive group;
moderately active RR = 0.79
(95% Cl, 0.58-l .07), highly active RR = 1.02
(95% Cl,O.66-1.58)

Null association across categories of physical
activity index

Null association across quartiles of physical
activity index

Inverse association; compared with walking
4 hrs/week, RR = 0.90 (95% Cl 0.69-l .17)
for walking l-4 hrs/week; RR = 0.73
(95% Cl 0.55-0.96) for walking > 4 hrs/week

Inverse association; adjusted risk estimate of
2.7-fold increased risk of CVD death for a
35 beat/min increase in heart rate for stage II
of exercise test

Inverse association; for men, age-adjusted RR
for lowest 20% compared with upper 40% =
7.9; for middle 40% = 2.5; for women, 9.2
and 3.6

Yes

Control for several confounding variables;
statistical significance only for men after
multivariate adjustment

Yes

Significant dose-response after adjusting for age,
smoking, and hypertension prevalence

Yes

Inverse association constant across all analyses;
inverse association maintained after multivariate
analyses

No

No statistical significance after controlling for
sociodemographic variables, BMI, and dietary
pattern

No

Point estimates adjusted for age, BMI, sex, and
smoking

No

No statistical significance after controlling for
several clinical and sociodemographic
confounding variables

Yes

Multivariate analysis adjusted for age, sex,
functional status, BMI, smoking, chronic
illnesses, and alcohol

Yes

Extensive control for clinical and
sociodemographic confounding influences

Yes

Significant linear dose-response association;
adjusted for age

89


Physical Activity and Health

Table 4-1. Continued

Study
Arraiz, Wigle,
Mao (1992)

Population
Stratified probability
sample of Canadians
aged 30-69 years,
conducted in 1978-
1979; 7-year follow-up

Definition of physical activity     Definition of
or cardiorespiratory fitness       cardiovascular disease

Submaximal aerobic capacity      Death due to CVD
estimated from home step test     (n = 37)

Sandvik et al.
(1993)

1,960 Norwegian men
aged 40-59 years;
average 16-year
follow-up

Maximal aerobic capacity
estimated by exercise test

Death due to CVD
(n = 144)

Blair et al.
(1995)

9,777 US men aged
20-82 years with 2
evaluations; 5.1 -year
average follow-up

Maximal aerobic capacity
estimated by exercise test

Death due to CVD
(ICD-9 390-449.9)
(n = 87)

Thirty-six studies examining the relationship of
physical activity level to risk of CHD have been
published since 1953 (Table 4-2). Studies published
before 1978 predominantly classified physical activ-
ity level byjob title or occupational activities. Studies
thereafter usually defined activity level by recall of
leisure-time activity or by such activity combined
with occupational activity. These later studies were
also able to control statistically for many potentially
confounding variables in addition to age. Most of
these studies focused on men in the age ranges
associated with increasingriskof CHD (30-75 years);
only four included women. Although in several stud-
ies, CHD mortality was the sole outcome variable,
most included both fatal and nonfatal disease. All but
one (Morris et al. 1973) were cohort studies; lengths
of follow-up from baseline assessment ranged from 4
to 25 years. All studies related a single baseline
estimate of physical activity level to risk of CHD
during the follow-up period.

Some study populations have had more than one
follow-up assessment for CHD. For example, three
follow-up assessments (at 10,12, and 23 years) have
been reported for men in the Honolulu Heart Pro-
gram (Yano, Reed, McGee 1984; Donahue et al. 1988;
Rodriguez et al. 1994). Each represented follow-up
further removed from the original determination of
physical activity. Thus, the diminishing effect seen
over time might indicate changing patterns of physical

activity- and thereby a lessening of validity of the
original physical activity classification (Table 4-2).
Oddly, in the 12-year follow-up, the reduction in
CHD risk observed among both active middle-aged
men (RR = 0.7) and active older men (RR = 0.4)
when compared with their least active counterparts
was not diminished by bivariate adjustment for
serum cholesterol, body mass index (BMI), or blood
pressure (Donahue et al. 1988). In the 23-year
follow-up, however, the reduction in CHD risk
among active men (RR = 0.8) was greatly diminished
by simultaneous adjustment for serum cholesterol,
BMI, blood pressure, and diabetes, (RR = 0.95),
leading the authors to conclude that the beneficial
effect of physical activity on CHD risk is likely
mediated by the beneficial effect of physical activity
on these other factors (Rodriguez et al. 1994). These
reports thus illustrate not only the problem of lengthy
follow-up without repeated assessments of physical
activity but also the problem of lack of uniformity in
adjustment for potential confounding factors, as well
as the underlying, thorny problem of adjustment for
multiple factors that may be in the causal pathway
between physical activity and disease. Studies have
in fact varied greatly in the extent to which they have
controlled for potential confounding and in the
factors selected for adjustment.
  Although early studies were not designed to dem-
onstrate a dose-response gradient between physical

90


The Effects of Physical Activity on Health and Disease

Main findings
Inverse association; relative to highest fitness
level, persons in "moderate" and "low"
categories had risks of 0.8 (95% Cl, 0.1-7.6)
and 5.4 (95% Cl, 1.9-l 5.9), respectively

Dose
response*

No

Adjustment for confounders
and other comments
Point estimates adjusted for age, BMI, sex, and
smoking

Inverse association; relative to men in lowest
fitness quartile, multivariate adjusted RR in
quartiles 2, 3, and 4 were 0.59, 0.45, and
0.41, respectively

Yes      Extensive control for confounding influences

Inverse association; relative to men who
remained unfit (lowest 20% of distribution),
those who improved had an age-adjusted RR

Yes

For each minute of improvement in exercise test
time, adjusted CVD mortality risk was reduced
8.6%

of 0.48 (95% Cl,`O.3 l-0.74)

Abbreviations: BMI = body mass index (wt [kg] /ht [ml2 ); CVD = cardiovascular disease: Cl = confidence interval; HMO = health
maintenance organization; ICD = International Classification of Diseases (8 and 9 refer to editions); RR = relative risk.
`A dose-response relationship requires more than 2 levels of comparison. In this column, "NA" means that there were only 2 levels of
comparison: "No" means that there were more than 2 levels but no dose-response gradient was found; "Yes" means that there were
more than 2 levels and a dose-response gradient was found.

activity level and CHD, most found an inverse asso-
ciation: more active persons were found to be at
lower risk of CHD than their more sedentary coun-
terparts. Of the 17 recent studies that found an
inverse relationship and were able to examine dose-
response relationships, 13 (76 percent) demonstrated
an inverse dose-response gradient between level of
physical activity and risk of CHD, whereas 2 showed
a dose-response gradient only for some subgroups.
The relationship between cardiorespiratory fit-
ness and risk of CHD was examined in seven cohort
studies (follow-up range, 4-20 years). All but two
(Lie, Mundal, Erikssen 1985; Erikssen 1986) used
estimates of aerobic power based on submaximal
exercise testing. None of these studies included
women. Similar to the studies of physical activity
and CHD, these all related a single baseline assess-
ment of cardiorespiratory fitness to risk of CHD
during the follow-up period. Most controlled statis-
tically for possible confounding variables. All seven
studies showed an inverse association between
cardiorespiratory fitness and CHD. Of the six
studies that had more than two categories of cardio-
respiratory fitness, all demonstrated an inverse
dose-response gradient.

Two recent meta-analyses of studies of physical
activity and CHD have included independent scoring
for the quality of the methods used in each study
(Powell et al. 1987; Berlin and Colditz 1990). Both
concluded that studies with higher-quality scores
tended to show higher relative risk estimates than
those with lower-quality scores. In the Berlin and
Colditz quantitative meta-analysis, the pooled rela-
tive risk for CHD-comparingrisk for the lowest level
of physical activity with risk for the highest level-
was 1.8 among the studies judged to be of higher
quality. In contrast, the pooled relative risk for the
studies with low-quality scores was in the null range.

CVD Risk Factors in Children

Because CHD is rare in children, the cardiovascular
effects of physical activity in children are assessed
through the relationship of physical activity with
CHD risk factors such as elevated low-density lipo-
protein cholesterol (LDL-C), lowered high-density
lipoprotein cholesterol (HDL-C), and elevated blood
pressure. The presence of CHD risk factors in chil-
dren is of concern because of evidence that athero-
sclerosis begins in childhood (Star-y 1989), that
presence of CHD in adults is related to elevated blood

91


Physical Activity and Health

Table 4-2.  Population-based studies of association of physical activity or cardiorespiratory fitness with coronary
       heart disease

Study

Population

Definition of physical activity
or cardiorespiratory fitness

Definition of coronary
heart disease

Kahn (1963)

Morris et al.
(1966)

Cassel et al.
(1971)

Physical activity

Morris et al.
(1953)

31,000 male employees
of London Transport
Executive aged 35-64
years

Morris and
Crawford (1958)

3,731 case necropsy
studies (decedents aged
45-70 years) conducted
in Scotland, England,
and Wales

Taylor et al.
(1962)

191,609 US white male
railroad industry
employees aged 40-64
years

2,240 Postal Service
employees in the
Washington, D.C., Post
Office between 1906
and 1940; followed
through December 1961

667 London bus
conductors and drivers
aged 30-69 years;
5-year follow-up

3,009 male residents
of Evans County,
Georgia, aged over 40
years in 1960-l 962;
7.25-year average
follow-up

Morris et al.
(1973)

British male executive
grade civil servants
aged 40-60 years;
232 heart attack case-
patients and 428
matched controls .

Brunner et al.
(1974)

5,288 male and 5,229
female residents of 58
Israeli kibbutzim aged
40-69 years; 15-year
follow-up

Occupational classification of job
duties: sedentary drivers and
active conductors

Physical activity at work defined
by coding of last known job title
before death (light, active, heavy)

Physical activity at work defined
by job title for clerks, switchmen,
and section men

Physical activity at work defined
by job title for clerks and carriers

Occupational classification of job
duties as sedentary drivers
and active conductors

Incidence of CHD
(n = 47)

Occupational classification of job   Incidence of CHD
duties as active or sedentary      (n = 337)

48-hour recall of leisure-time
physical activities; activities
defined as capable of reaching
7.5 kcal/min were defined as
vigorous

Work types classified as sedentary
or nonsedentary

First clinical episode of
CHD

Necropsy evaluation of
IMF among persons
dying from
noncoronary causes

Death due to
arteriosclerotic disease
(ICD 420, 422)
in 1955-l 956

Death due to CHD

First CHD attack
(fatal and nonfatal)

Fatal and nonfatal CHD,
males (n = 281) and
females (n = 70)

92


The Effects of Physical Activity on Health and Disease

Main findings

Dose     Adjustment for confounders
response*   and other comments

Inverse association; relative to men whose
main job responsibility was driving buses,
conductors had an age-adjusted risk of first
coronary episode of 0.70

Inverse association; RR for IMF for persons
in light occupations was 1.97 relative to
heavy group; active group rate was
intermediate

Inverse association; RR for arteriosclerotic
disease among clerks was 2.03 relative to
that for section men; risk estimate for
switchmen was 1.46

Inverse and null associations; among
employees classified by their original
occupational category, the age-adjusted risk
for CHD death for clerks relative to carriers
was 1.26

Inverse association; age-adjusted risk of CHD
incidence among drivers was 1.8 relative to
that for conductors

Inverse association; age-adjusted risk of CHD
among sedentary, nonfarm occupations
relative to that for active nonfarm
occupations was 1.8

Inverse association; RR estimate for first
attack among vigorous group = 0.33
compared with nonvigorous group

Inverse association; risk for CHD incidence
among those engaged in sedentary work
compared with that for nonsedentary peers
was 2.52 for men and 3.28 for women

NA

No control for confounding; results were
similar in subgroup of men who died of
CHD-associated conditions

Yes

No control for confounding; one of few
pathology studies

Yes

NA

NA

NA

NA

No control for confounding; specific analyses
were consistent with overall results

No control for confounding; extensive efforts
made to consider and evaluate job transfers

Medical evaluation data used to control
for confounding variables

Data also available on black residents;
comparisons between sedentary and active
occupations not possible

Only study to analyze 48-hour recall
of leisure-time physical activity
(5-minute intervals)

NA

No differences in serum cholesterol
and body weight between groups

93


Physical Activity and Health

Table 4-2. Continued
                   Definition of physical activity    Definition of coronary
Study       Population       or cardiorespiratory fitness      heart disease

Paffenbarger and
Hale (1975)

Paffenbarger et al.
(1977)

Rosenman, Bawol,
Oscherwitz
(1977)

Chave et al.
(1978)

Paffenbarger,
Wing, Hyde
(1978)

Morris et al.
(1980)

Salonen et al.
(1982)

Pomrehn et al.
(1982)

6,351 San Francisco
Bay Area longshoremen
aged 35-74 years;
followed for 22 years,
from 1951 to death
or to age 75

3,686 San Francisco
Bay Area longshoremen
aged 35-74 years;
followed for 22 years,
from 195 1 to death
or to age 75

2,065 white male San
Francisco Bay Area
federal employees aged
35-59 years; 4-year
follow-up

3,591 British male
executive-grade civil
servants aged 40-64
years; 8.5-year average
follow-up from
1968 to 1970

16,936 Harvard male
alumni aged 35-74
years; followed up for
6-l 0 years

17,944 British male
executive grade civil
servants aged 40-64
years; 8.5-year average
follow-up from
1968 to 1970

3,829 women and
4,110 men aged 30-59
years from Eastern
Finland; 7-year
follow-up

61,922 deaths from
1964-l 978 among
Iowa men aged 20 to
64 years

Work-years according to
required energy output: heavy
(5.2-7.5 kcal/min), moderate
(2.4-5.0 kcal/min), and light
(1.5-2.0 kcal/min)

Work-years according to
required energy output: high
(5.2-7.5 kcal/min), intermediate
(2.4-5.0 kcaI/min), and light
(1.5-2.0 kcal/min)

Occupational physical activity;,
estimated caloric expenditure for
work and nonwork activity

48-hour leisure-time physical
activity recall; activities capable
of reaching 7.5 kcal/min defined
as vigorous

Physical activity index based on
self-report of stairs climbed, blocks
walked, and strenuous sports play

48-hour recall of leisure-time
physical activities; activities
defined as capable of reaching
7.5 kcal/min were defined as
vigorous

Dichotomous assessment of
occupational and leisure-time
physical activity (low/high)

Occupational classification;
farmers vs. nonfarmers

CHD death (ICD-7 420)
(n = 598)

CHD death ([CD-7 420)
(n = 395)
     i

Fatal and nonfatal CHD
(n = 65)

Fatal and nonfatal first
CHD attack (n = 268)

Fatal and nonfatal first
heart attack (n = 572)

Fatal and nonfatal first
heart attack (n =l ,138)

Fatal acute ischemic heart
disease (ICD-8, 410-412)
(n = 89 men and 14 women)
and acute myocardial
infarction (ICD-8,41 O-41 1)
(n = 210 men and 63 women)

Death from ischemic
heart disease

94


The Effects of Physical Activity on Health and Disease

Main findings

Dose     Adjustment for confounders
resuonse'   and other comments

Inverse association; relative to heavy
category, age-adjusted RR of CHD death was
1.70 in moderate and 1.80 in light categories

Yes

No control for confounding variables; efforts
made to evaluate job changes in the cohort
over time

Inverse association overall, inverse for
younger birth cohorts and null for older
cohorts; relative to high category,
age-adjusted RRs of CHD death were 1.8
in intermediate and 1.60 in light categories

No/Yes

Dose response noted in age-adjusted rates
only for two younger groups; two older
groups exhibited no association

Null association

No

Relatively short-term follow-up

Inverse association; risk of CHD attack
among men reporting nonvigorous exercise
relative to men reporting vigorous exercise
was 2.2

NA

Inverse association; age-adjusted RR of first     Yes
heart attack for men who expended fewer than
2,000 kcal/week was 1.64 compared with
men who expended 2,000 or more kcal/week

Inverse association; age-adjusted risk
of CHD attack among men reporting
nonvigorous exercise relative to those
reporting vigorous exercise was 2.2

NA

Inverse association; RR of acute
myocardial infarction for men and women
with low levels of physical activity at work =
1.5 (90% Cl, 1.2-2.0) for men and 2.4
(90% Cl, 1.5-3.7) for women

NA

Preliminary report of further data of
Morris et al. 1980

History of athleticism not associated with
lower risk unless there was also current
energy expenditure

Increased risk similar for fatal and
nonfatal attacks

No associations with leisure-time physical
activity; extensive adjustment for
confounding

Farm men had significantly less mortality than   NA      No adjustment for confounding
expected from the experience in the general
Population of Iowa men (SMR = 0.89)

95


Physical Activity and Health

Table 4-2. Continued
                   Definition of physical activity    Definition of coronary
Study        Population       or cardiorespiratory fitness       heart disease

Garcia-Palmieri
et al. (1982)

Paffenbarger et al.
(1984)

Yano, Reed,
McGee (1984)

Menotti and
Seccareccia
(1985)

Kannel et al.
(1986)

Lapidus and
Bengtsson (1986)

Leon et al.
(1987)

Pekkanen et al.
(1987)

Sobolski et al.
(1987)

8,793 Puerto Rican
men aged 45-64 years;
followed for up to 8.25
years

16,936 US male college
alumni who entered
college between 1916
and 1950; followed
from 1962 to 1978

7,705 Hawaiian men of
Japanese ancestry aged
45-68 years with no
history of heart disease;
1 O-year follow-up

99,029 Italian male
railroad employees
aged 40-59 years;
S-year follow-up

1 ,166 Framingham (MA)
men aged 45-64 years.;
24-year follow-up

1,462 Swedish women
aged 38-60 years;
follow-up between
1968 and 1981

12,138 North American  Leisure-time physical activity
men at high risk for    index; energy expenditure
CHD, aged 35-57 years;  (minutes/week)

Usual 24hour physical activity
index based on hours/day at
specific intensity

Physical activity index estimated
from reports of stairs climbed,
city blocks walked, and sports
played each week

Self-report of 24hour habitual
physical activity in 1965-l 968

Occupational physical activity
(heavy, moderate, sedentary)

Physical activity index based on
hours per day at activity-specific
intensity; occupational physical
activity classified by physical
demand of work

Physical activity at work and
during leisure hours, lifetime, and
during previous years

7-year average follow-up

636 apparently healthy  Occupational and transport/
Finnish men aged     recreational physical activity
45-64 years, followed  (high or low)
for 20 years from   .
1964 baseline

2,109 Belgian men
aged 40-55 years in
1976-l 978; 5-year
follow-up

Occupational and leisure-time
physical activity (4 categories
each)

CHD incidence other than
angina pectoris (n = 335)

Death due to CHD
(n = 441)

Incident cases of fatal and
nonfatal CHD (n = 511)

Fatal myocardial infarction
(n = 614)

Death due to CHD
(n = 220)

Nonfatal myocardial
infarction and angina
pectoris

Fatal and nonfatal CHD
(n = 781; 368 fatal)

Death due to CHD
(n = 106)

Incident cases of fatal and
nonfatal myocardial
infarction and sudden
death (n = 36)

96


The Effects of Physical Activity on Health and Disease

                              Dose
Main findings                response'
Inverse association; physical activity index     Yes
was significantly related to lower risk of CHD
in urban as well as rural men

Inverse association; relative to highest
category of index (2,000+ kcal/week),
risk estimates in next two lower categories
were 1.28 and 1.84, respectively

Yes

Inverse association; significant only for all
CHD; no significant association for various
subtypes

NA

Inverse association; relative to sedentary,
men in moderate and heavy occupational
activity had RRs of 0.97 and 0.64,
respectively

Yes

Inverse association; age-adjusted RR (relative   Yes
to high category) = 1.38 (low), 1.21 (moderate);
for occupational activity, age-adjusted RR
(relative to heavy category) = 1.27 (sedentary),
1.22 (light), 0.99 (medium)

Inverse association only for leisure-time
physical activity; RR = 2.8 (95% Cl, 1.2-
6.5) comparing low leisure-time physical
activity with all other categories

NA      Adjusted for age

Inverse association; multivariate adjusted
risk estimate (relative to low activity tertile)
was 0.90 (95% Cl, 0.76-l .06) for more
active and 0.83 (95% Cl, 0.70-0.99) for
most active

Yes

Inverse association; adjusted RR for men
in low physical activity group was 1.30
fp = 0.17)

NA

Null association for both leisure-time and
occupational physical activity

No

Adjustment for confounders
and other comments

Significant inverse relationship for CHD
after multivariate adjustment

Significant dose-response after adjusting for
age, smoking, and hypertension prevalence

Adjusted for age, blood pressure, cholesterol,
BMI, serum glucose, vital capacity, etc.

Adjusted for age

Inverse association constant across all
analyses and maintained after controlling
for multivariate confounding

Dose response for fatal and nonfatal cases
combined but not for CHD death or sudden
death separately

Association limited to second half
of follow-up period

One of two studies to simultaneously
evaluate associations of physical activity,
fitness, and CHD

97


Physical Activity and Health

Table 4-2. Continued
                   Definition of physical activity    Definition of coronary
Study       Population       or cardiorespiratory fitness      heart disease

Donahue et al.
(1988)

Salonen et al.
(1988)

lohansson et al.
(1988)

Slattery, Jacobs,
Nichaman
(1989)

Morris et al.
(1990)

Lindsted,
Tonstad,
Kuzma
(19911

Shaper and
Wannamethee
(1991)

Seccareccia and
Menotti (1992)

Hein,
Suadicani,
Gyntelberg
(1992)

7,644 Hawaiian men of
Japanese ancestry aged
45-64 years with no
history of heart disease;
12-year follow-up

15,088 Eastern Finnish
men and women aged
30-59 years; 6-year
follow-up

7,495 Goteburg men
aged 47-55 years at
entry; 11.8-year
average follow-up

3,043 US male
railroad employees;
followed for
17-20 years

9,376 British male
middle grade
executives aged 45-64
years; 9.3-year
average follow-up

9,484 Seventh-Day
Adventist men aged
2 30 years; 26-year
follow-up

7,735 British men aged
40-59 years; 8.5-year
follow-up

1,712 men from
Northern and Central
Italy, aged 40-59 years,
initially examined in
1960; 25-year follow-up

4,999 Copenhagen
men aged 40-59 years;
17-year follow-up

Self-report of 24hour habitual
physical activity in 1965-l 968;
3-point scale defined by tertiles
of distribution

Self-reported leisure-time and
occupational physical activity
(4 levels collapsed into 2
categories each)

Physical activity at work and
physical activity during leisure
time (4-point scale for each)

Leisure-time physical activity
index (kcal/week)

Leisure-time physical activity
reported over previous 4 weeks;
energy expenditure values
ascribed to reported activities

Self-report to single physical
activity question

Self-report of physical activity at
baseline; 6-point scale

Occupational physical activity
(self-report): sedentary,
moderate, and heavy

Leisure-time physical activity
(4-point scale)

Incident cases of fatal
and nonfatal CHD
(n = 444)

Death due to CHD

(ICD-8 41 O-41 4)
(n=102
90 men, 12 women)

Incident cases of fatal
and nonfatal CHD

Death due to CHD
(ICD-8 41 o-41 4)

Fatal and nonfatal CHD
(ICD-8 41 o-41 4)
(n = 474)

lschemic heart disease
mortality
(ICD-8 410-414)
(n = 1,351)

Fatal and nonfatal heart
attack (n = 488)

Death due to CHD

Fatal myocardial
infarction
(ICD-8 41 o-41 4)
(n = 266)

from 1970/l 971

98


The Effects of Physical Activity on Health and Disease

Dose     Adjustment for confounders

Main findings

response*

and other comments

Inverse association; RR among active men
relative to sedentary men was 0.69 (95% Cl,
0.53-0.88) for men aged 45-64 and 0.43
(95% Cl, 0.1 g-0.99) for older men aged 65-74

Inverse association; occupational: adjusted
RR among inactive was 1.3 (95% Cl,
1.1-1.6) relative to active; adjusted RR of
CHD among leisure-time active was 1.2
(95% Cl, 1.0-l .5)

Null association between physical activity at
work and CHD risk; inverse association (not
statistically significant) between leisure-time
physical activity and CHD

Inverse association; adjusted risk estimate
(relative to highest physical activity category)
was 1.28 for sedentary group (not statistically
significant)

Inverse association; age-adjusted RR for
3 episodes per week of vigorous physical
activity relative to sedentary group was 0.36

Null association; risk estimates of CHD
death exhibited a U-shaped relationship
with increasing physical activity levels

Inverse association only for 2 activity levels;
RR compared with sedentary for increasing
physical activity levels: occasional 0.9
(95%CI, 0.5-l .3), light 0.9 (95% Cl, 0.6-l .4),
moderate 0.5 (95% Cl, 0.2-0.8), moderately
vigorous 0.5 (95% Cl, 0.3-0.9), and
vigorous 0.9 (95% Cl, 0.5-l .8)
Inverse association; age-adjusted RRfor
moderate and heavy categories compared
with that for sedentary group was 0.69 and
0.58, respectively

Inverse association; relative to more active
men (categories 2-4 of index), least active
men had an adjusted RR of CHD of 1.59
(95% Cl, 1.14-2.21)

Yes

Adjusted for age, alcohol use, and smoking;
bivariate adjustment for cholesterol, BMI,
and blood pressure did not alter findings;
follow-up to Yano, Reed, McGee (1984)

NA

Point estimate for low leisure-time physical
activity was adjusted toward the null after
consideration of other CHD risk factors

No

Extensive control for confounding variables;
ancillary analysis on postinfarction patients
also yielded null association

Yes

Adjusted for age, smoking, cholesterol,
and blood pressure

Yes

No adjustment for confounding; association
only noted for vigorous physical activity

No

No

Yes

Possible protective association among
moderate activity group

No clear linear trend

Inverse association remained statistically
significant after adjustment for confounding

No

One of two studies to simultaneously
evaluate activity and fitness in relation
to CHD mortality

99


Physical Activity and Health

Table 4-2. Continued
                   Definition of physical activity    Definition of coronary
Study       Population       or cardiorespiratory fitness      heart disease

Shaper,
Wannamethee,
Walker (1994)

5,694 British men aged
40-59 years; 9.5-year
follow-up

Rodriguez et al.
(1994)

7,074 Hawaiian men
of Japanese ancestry
aged 45-68 years;
23-year follow-up

Cardiorespiratory fitness
Peters et al.
(1983)

2,779 male Los Angeles
County public safety
employees aged
< 55 years; 4.8-year
average follow-up

Lie, Mundal,
Erikssen
(1985)

Erikssen (1986)

Sobolski et al.
(1987)

Ekelund et al.
(1988)

Slattery et al.
(1988)

2,431 US male railroad
employees; 17- through
20-year follow-up

Hein,        4,999 Copenhagen
Suadicani,      men aged 40-59 years;
Gyntelberg     17-year follow-up
(1992)         from 1970/l 971

2,014 Norwegian
employed men aged
40-59 years; 7-year
follow-up

1,832 Norwegian
men aged 40-59 years;
-/-year average
follow-up

2,109 Belgian men
aged 40-55 years in
1976-l 978; 5-year
follow-up

3,106 North American
men aged 30-69 years;
8.5-year average
follow-up

Self-report of physical activity at
baseline; 6-point scale data
analyzed by hypertensive status

Self-report of 24hour habitual
physical activity in 1965-l 968

Submaximal aerobic capacity
estimated from cycle ergometer
test; age-specific median split used
to determine low/high fitness

Near maximal cycle ergometer
exercise test; total work in
quartiles

Near maximal cycle ergometer
exercise test; total work in
quartiles

Submaximal aerobic capacity
estimated from cycle ergometry
test

Submaximal aerobic capacity
estimated from exercise test

Submaximal exercise heart rate on
standard (3 min) treadmill test
evaluation

Submaximal aerobic capacity
estimated from cycle ergometer
exercise test

Fatal and nonfatal heart
attack (n = 311; 165
normotensive, 146
hypertensive)
Incident cases of fatal
and nonfatal CHD
(n = 340)

Incident cases of fatal
and nonfatal myocardial
infarction (n = 36)

Incident cases of fatal
and nonfatal CHD

Incident cases of fatal
and nonfatal myocardial
infarction and CHD death

Incident cases of fatal
and nonfatal myocardial
infarction and sudden
death (n = 36)

Death due to CHD
(ICD-8 41 o-41 4)

Death due to CHD
(ICD-8 41 o-41 4)

Fatal myocardial infarction
(ICD-8 41 o-41 4)
(n = 266)

100


The Effects of Physical Activity on Health and Disease

Main findings

Dose     Adjustment for confounders
response*    and other comments

Inverse association; statistically significant
trend among nonhypertensive participants,
U-shaped association among hypertensive
participants

Inverse association when adjusted only for
age; null association when adjusted for
cholesterol, blood pressure, BMI, diabetes,
etc.

inverse association; RR for CHD incidence in
low fitness group was 2.2 (95% Cl, 1.1-4.7)
compared with high fitness

Inverse association; point estimates and
significance not reported

Inverse association; point estimates and
significance not reported

Inverse association; RR for myocardial
infarction and sudden death in low fit
group was 1.6 relative to high fit

Inverse association; adjusted risk estimate of
3.2-fold increased risk of CHD death for a
35 beat/min increase in heart rate for stage II
of exercise test

Inverse association; adjusted risk estimate for
highest heart rate response group relative to
lowest was 1.20 (95% Cl, 1 .l O-l .26)

Inverse association; relative to more fit men,
least fit men had an adjusted risk of 1.46
(95% Cl, 0.94-2.26)

Yes/No

In hypertensive men, the protective
effect of physical activity was eliminated
with vigorous activity

No

Follow-up report to that of Yano, Reed,
McGee (1984) and Donahue et al. (1988)

NA

Yes

Yes

Similar results seen when men with
electrocardiogram evidence of heart
disease were excluded

No adjustment for confounding variables

No adjustment for confounding variables

Yes

One of two studies to simultaneously
evaluate associations of activity, fitness,
and CHD

Yes

Extensive control for confounding
influences

Yes

Risk estimate attenuated substantially after
adjustment for other CHD risk factors

Yes

One of two studies to simultaneously
evaluate activity and fitness in relation
to CHD mortality

Abbreviations: BMI = Body mass index (wt [kg/ /ht [ml2 ); CHD = coronary heart disease; Cl = confidence interval; ICD = International
Classification of Diseases (8 and 9 refer to editions); IMF = ischemic myocardial fibrosis; RR = relative risk.
`A dose-response relationship requires more than 2 levels of comparison. In this column, "NA" means that there were only
2 levels of comparison; "No" means that there were more than 2 levels but no dose-response gradient was found: "Yes" means
that there were more than 2 levels and a dose-response gradient was found.

101


Physical Activity and Health

lipids in children (Lee, Lauer, Clarke 1986), and that
CHD risk factor patterns persist from childhood to
adulthood (Webber et al. 1991; Mahoney et al. 1991).
Recently, Armstrong and Simons-Morton (1994)
reviewed the research literature on physical activity
and blood lipids in children and adolescents, includ-
ing over 20 observational and 8 intervention studies.
They concluded that the cross-sectional observa-
tional studies did not demonstrate a relationship
between physical activity level or cardiorespiratory
fitness and total cholesterol, LDL-C, or HDL-C,
especially when differences in body weight or fat
were taken into account, suggesting that activity and
body fat are not independently related to serum
lipids. However, highly physically active or fit chil-
dren and adolescents tended to have higher HDL-C
than their inactive or unfit peers. The intervention
studies generally showed favorable effects of exer-
cise on LDL-C or HDL-C -only in children and
adolescents who were at high risk for CHD because
of obesity, insulin-dependent diabetes mellitus, or
having a parent with three or more CHD risk factors.
  Alpert and Wilmore (1994) recently reviewed
the research literature on physical activity and blood
pressure in children and adolescents; including 18
observational and 11 intervention studies. These
authors found evidence in studies of normotensive
children and adolescents that higher levels of physi-
cal activity tended to be related to lower blood
pressure. The associations were generally reduced in
magnitude in those studies that adjusted for BMI,
suggesting that lower body far mass may at least
partly explain why physical activity is related to
lower blood pressure. Intervention studies tended to
show that training programs lowered blood pressure
by 1-6 mm Hg in normotensive children and adoles-
cents, although the effects were inconsistent for boys
and girls and for systolic and diastolic blood pres-
sure. In hypertensive childrenand adolescents, physi-
cal activity interventions lowered blood pressure to
a greater degree than in their normotensive peers
(by approximately 10 mm Hg), although statistical
significance was not always achieved because of
small sample sizes.

Interpreting these studies on lipids and blood
pressure in children and adolescents is hindered by
several factors. Studies used a variety of physical
activity categorizations, and the interventions cov-
ered a wide range of frequency, type, duration, and

intensity, which were not all specified. The difficul-
ties of assessing physical activity by self-report in
children and adolescents, together with the highly
self-selected population in the observational studies,
may account for the less consistent findings on lipids
and physical activity that were reported for children
and adolescents than for adults. The relationship
between dose of physical activity and amount of
effect on blood pressure or serum lipids in children
has not been adequately addressed.
Nonetheless, there appears to be some evidence,
although not strong, of a direct relationship between
physical activity and HDL-C. level in children and
adolescents. There is also evidence that increased
physical activity can favorably influence the lipid
profile in children and adolescents who are at high
risk of CHD. Similarly, the evidence suggests that
physical activity can lower blood pressure in chil-
dren and adolescents, particularly in those who have
elevated blood pressure.

Stroke

A major cardiovascular problem in developed coun-
tries, stroke (ischemic stroke and hemorrhagic stroke)
is the third leading cause of death in the United States
(NCHS 1994). Atherosclerosis of the extracranial
and intracranial arteries, which triggers thrombosis,
is thought to be the underlying pathologic basis of
ischemic stroke. Cigarette smoking and high blood
pressure are major risk factors for ischemic stroke,
whereas high blood pressure is the major determi-
nant of hemorrhagic stroke. The studies cited in this
section examined the association between reported
level of physical activity and stroke. No published
studies have examined the association between car-
diorespiratory fitness and stroke.
Fourteen population-based studies (four that
include women) relate physical activity to risk of all
types of stroke; these closely parallel the study
designs and populations previously cited for CVD
and CHD (Table 4-3). Thirteen of the studies were
cohort studies (follow-up range, 5-26 years). Only
eight found an inverse association. As with the
earlier studies on CHD, the earlier studies of stroke
did not permit a dose-response evaluation. Among
later studies that could do so by virtue of design,
half did not find a gradient. This outcome, coupled
with some suggestion of a "U-shaped" association

102


in two studies (Menotti and Seccareccia 1985;
Lindsted, Tonstad, Kuzma 199 l), casts doubt on the
nature of the association between physical activity
and risk of both types of strokes combined.
Because of their different pathophysiologies,
physical activity may not affect ischemic and hemor-
rhagic stroke in the same way; this issue requires
more research. Only one study distinguished be-
tween ischemic and hemorrhagic stroke (Abbott et
al. 1994). In this study, inactive men were more likely
than active men to have a hemorrhagic stroke; physi-
cal activity was also associated with a lower risk of
ischemic stroke in smokers but not in nonsmokers.
Thus the existing data do not unequivocally
support an association between physical activity and
risk of stroke..

High Blood Pressure

High blood pressure is a major underlying cause of
cardiovascular complications and mortality. Organ
damage and complications related to elevated blood
pressure include left ventricular hypertrophy (which
can eventually lead to left ventricular dysfunction
and congestive heart failure), hemorrhagic stroke,
aortic aneurysms and dissections, renal failure, and
retinopathy. Atherosclerotic complications of high
blood pressure include CHD, ischemic stroke, and
peripheral vascular disease. Although rates of hyper-
tension have been declining in the United States
since 1960, nearly one in four Americans can be
classified as being hypertensive (DHHS 1995).

Prospective observational studies relating physi-
cal activity level or cardiorespiratory fitness to risk
of hypertension are summarized in Table 4-4.
Several cohort studies have followed male college
alumni after graduation. One found later develop-
ment of hypertension to be inversely related to the
reported number of hours per week of participation
in sports or exercise while in college (Paffenbarger,
Thorne, Wing 1968). In a later follow-up of the
same cohort, using information'on physical ac-
tivity during mid-life, vigorous sports were asso-
ciated with a 19-30 percent reduction in risk of
developing hypertension over the 14-year period
(Paffenbarger et al. 1991). Follow-up of a different
cohort of male college alumni similarly showed the
least active men to have a 30 percent increased risk
of developing hypertension (Paffenbarger et al.

The Effects of Physical Activity on Health and Disease

1983). In a study of 55- through 69-year-old women
followed for 2 years, the most active women were
found to have a 30 percent reduced risk of develop-
ing hypertension (Folsom et al. 1990).
One randomized trial for the primary prevention
of hypertension has been conducted. A 5-year trial of
a nutrition and physical activity intervention showed
that the incidence of hypertension for the interven-
tion group was less than half that of the control group
(Stamler et al. 1989). Participants in the intervention
group lost more weight than those in the control
group, reduced more of their sodium and alcohol
intake, and were more likely to become more physi-
cally active. Although the effects of the nutritional
and physical activity components of this interven-
tion cannot be separated, the study does show that
the risk for developing hypertension among persons
who are at high risk for the disease can be lowered by
weight loss and improvements in dietary and physi-
cal activity practices.

Like physical inactivity, low cardiorespiratory
fitness in middle age is associated with increased risk
for high blood pressure. After adjustment for sex,
age, baseline blood pressure, and body mass index,
persons with low cardiorespiratory fitness had a 52
percent higher risk of later developing high blood
pressure than their fit peers (Blair et al. 1984).
Taken together, the cohort studies show that
physical inactivity is associated with an increased
risk of later developing hypertension among both
men and women. Three of the studies had more than
two categories of physical activity for comparison,
and each demonstrated a dose-response gradient
between amount of activity and degree of protection
from hypertension. Point estimates for quantifica-
tion of risk suggest that those least physically active
have a 30 percent greater risk of developing hyper-
tension than their most active counterparts. Unfor-
tunately, none of these studies was conducted in
minority populations, which have a disproportion-
ate burden of hypertensive disease (DHHS 1995).
  Several randomized controlled trials have been
conducted to determine the effects of exercise on
blood pressure in people with elevated blood pres-
sure levels. The reduction of elevated blood pressure
is important for preventing stroke and CHD, for
which high blood pressure is a risk factor with a
dose-response relationship (NIH 1992). Thirteen

103


Physical Activity and Health

Table 4-3.  Population-based studies of association of physical activity with stroke (CVA)
                        Definition of              Definition of
Study       Population       physical activity            stroke

Paffenbarger and
Williams (1967)

Paffenbarger
(1972)

Kannel and
Sorlie (1979)

Salonen et al.
(1982)

Herman et al.
(1983)

Paffenbarger et al
(1984)

Menotti and
Seccareccia
(1985)

Lapidus and
Bengtsson
(1986)

Menotti et ai.

(1990)

> 50,000 US male
college alumni
aged 30-70years

3,991 US longshoremen
aged 35 years and older;
18.5-year follow-up
from 1951

1,909 Framingham (MA)
men aged 35-64 at
4th biennial examina-
tion; 14-year follow-up

3,829 women and
4,110 men aged 30-59
years from Eastern
Finland; 7-year
follow-up

132 hospitalized Dutch
stroke case-patients and
239 age- and sex-.
matched controls; men
and women aged
40-74 years

16,936 US male college
alumni who entered
college between 1916
and 1950; followed
from 1962-l 978

99,029 Italian males
railroad employees
aged 40-59 years;
5-year follow-up

1,462 Swedish women
aged 38-60; follow-up
between 1968 and 1981

8,287 men aged 40-59
years in six of seven
countries from Seven
Countries Study;
20-year follow-up

Participation in college varsity
athletics (yes/no)

Occupational activity (cargo
handler or not)

Physical activity index based on
hours per day spent at activity-
specific intensity

Dichotomous assessment of
occupational physical activity
(low/high)

Leisure-time physical activity
(greatest portion of one's lifetime)
ranging from little to regular-heavy

Physical activity index estimated
from reports of stairs climbed, city
blocks walked, and sports played
each week

Classification of occupational
physical activity (heavy, moderate,
sedentary)

Work and leisure physical activity
assessed via 4-scales for lifetime
and for the time before 1968
baseline

Classification of occupational
physical activity (heavy, moderate,
sedentary)

Hemorrhagic and
ischemic stroke death
(n = 171)

Hemorrhagic and
ischemic stroke death
(n = 132)

Cerebrovascular accident
(n = 87)

Cerebral stroke
(ICD-8 430-437) morbidity
and mortality among men
(n = 71) and women
(n = 56)

Rapidly developed clinical
signs of focal or global
disturbance of cerebral
function lasting more
than 24 hours or leading
to death with no apparent
cause other than
vascular origin

Death due to stroke
(n = 103)

Fatal stroke (n = 187)

Fatal and nonfatal stroke
(n = 13)

Fatal stroke
(cohort analysis)

104


The Effects of Physical Activity on Health and Disease

Main findings

Dose     Adjustment for confounders
response*    and other comments

Inverse association; nondecedents were 2.2
times as likely to have participated in varsity
sports than were decedents; hemorrhagic
strokes = 2.1, occlusive strokes = 2.5

Noncargo handlers were 1.11 times as likely
as cargo handlers to die from stroke

Inverse association between physical activity
index and 14-year incidence of stroke

Inverse association with statistically significant
RRs for men and women with low levels of
physical activity at work were-l.5 (95% Cl,
1.2-2.0) for men and 2.4 (95% Cl, 1.5-3.7)
for women

Inverse association; relative to lowest
physical activity category, risk estimates were
0.72 (95% Cl, 0.37-l .42) for moderate and
0.41 (95% Cl, 0.21-0.84) for high categories

Inverse association; relative to highest
category of index (2,000+ kcal/week), risk
estimates in next two lower categories were
1.25 and 2.71, respectively

Nonlinear "U" shape association; relative to
sedentary category, men in moderate and
heavy occupational activity categories had
risks of 0.65 and 1 .O, respectively

Inverse association; women with low physical
activity at work were 7.8 times as likely as
others to have stroke (95% Cl, 2.7-23.0);
womenwith low physical activity leisure were
10.1 times as likely as others to have stroke
(95% Cl, 3.8-27.1)

Null association

NA

Results adjusted for age only

NA

Results adjusted for age only

Yes

No statistical significance ,after controlling
for several confounding variables

NA

Evidence for inverse association for low
activity during leisure time, but no statistical
significance after adjustment for other factors

Yes

Adjusted for a variety of potential
confounding influences

Yes

No

Significant dose-response trend after adjusting
for differences in age, cigarette smoking, and
hypertension prevalence

Age-adjusted only

NA

Age-adjusted only

No

No association after statistical adjustment
for risk factors

10.5


Physical Activity and Health

Table 4-3. Continued

                          Definition of              Definition of
Study       Population       physical activity             stroke

Harmsen et al.
(1990)

Lindsted,
Tonstad,
Kuzma,
(1991)

Wannamethee
and Shaper
(1992)

Abbott et al.
(1994) j

Kiely et al.
(1994)

7,495 Swedish men
aged 47-55 years at
baseline examination;
11.8-year average
follow-up

9,484 male Seventh-
Day Adventists aged
2 30 years; 26year
follow-up

7,735 British men aged
40-59 years; 8.5-year
follow-up

7,530 Hawaiian men of
Japanese ancestry aged
45-68 years; 22-year
follow-up

Four cohorts of
Framingham (MA) men
and women: cohort I-
1,897 men aged 35-69
years; cohort II-2,299
women aged 35-68
years; cohort Ill-men
aged 49-83 years;
cohort IV-women
aged 49-83 years;
follow-up for cohorts I
and II up to 32 years,
for cohorts III and IV
up to 18 years

Physical activity at work and
leisure hours (low, high)

Self-report of physical activity
level in 1960 (highly active,
moderately active, low activity)

Self-report of physical activity at
baseline; 6-point scale defined on
the basis of type and frequency
of activity

Self-report of 24hour habitual
physical activity in 1965-l 968
(inactive, partially active, active)

Self-report of daily activity level;
composite score formulated from
index and categorized into high,
medium, and low physical activity

Fatal stroke
(all and subtypes)
(n = 230)

Fatal stroke (n = 410)

Fatal and nonfatal stroke
(n = 128)

Fatal and nonfatal
neurologic deficit
with sudden
occurrence and remaining
present for at least 2 weeks
or until death (subtypes)
(n = 537)

Fatal and nonfatal
first occurrence of
atherothrombotic brain
infarction, cerebral
embolism, or other stroke
(cohort I, n = 195;
cohort II, n = 232;
cohort III, n = 113;
cohort IV, n = 140)

106


The Effects of Physical Activity on Health and Disease

Main findings

Dose     Adjustment for confounders
response*    and other comments

Null association; relative to low physical
activity category, slightly elevated estimates
were observed for all strokes and subtypes
for high activity group

Nonlinear "U" shape association; relative to
low activity level, risk estimates were 0.78
(95% Cl, 0.61-l .OO) for moderate activity
and 1.08 (95% Cl, 0.58-2.01) for high activity

Inverse association; statistically significant
linear trend of lower risk of stroke with higher
physical activity scale

Null association seen for all strokes and all
subtypes for men aged 45-54 years

Inverse association seen for all strokes and
subtypes for men aged 55-68 years

Risk estimate relative to low
physical activity group:
cohort l-nonsignificant inverse association
for medium group = 0.90 (0.62-l .31)
and for high group = 0.84 (0.59-l .18);
cohort II-nonsignificant nonlinear association
for medium group = 1.21 (0.89-l .63)
and for high group = 0.89 (0.60-l .3 1);
cohort Ill-significant inverse association
for medium group = 0.41 (0.24-0.69)
and for high group = 0.53 (0.34-0.84);
cohort IV-nonsignificant nonlinear association
for medium group = 0.97 (0.64-l .47)

and for high group = 1.21

Abbreviations: BMI = body mass index (wt [kg] /ht [ml2 ); CVA = cerebrovascular accident; Cl = confidence interval; ICD = International
Classification of Diseases (8 and 9 refer to editions); RR = relative risk.
`A dose-response relationship requires more than 2 levels of comparison. In this column, "NA" means that there were only 2 levels of
comparison; "No" means that there were more than 2 levels but no dose-response gradient was found; "Yes" means that there were
more than 2 levels and a dose-response gradieht was found.

No

No

Yes

Yes, in
older

No in
younger

Yes, C I
Yes, C I

No, C II
No, C II
Yes, C III

No, C IV

No association after statistical adjustment
for risk factors

Adjusted for sociodemographic factors, BMI,
and dietary pattern

Linear trend observed in men both with and
without existing ischemic heart disease

No association of physical activity to risk
of stroke in older smokers

Control for many confounding factors;
nonlinear association in women only
(cohorts III and IV); suggestion of threshold
relationship (cohort III)

107


Physical Activity and Health

Table 4-4. Population-based cohort studies of association of physical activity with hypertension
                        Definition of              Definition of
study -    Population       physical activity         hypertension

Paffenbarger,
Thorne,
Wing
(1968)

7,685 men who
attended the University
of Pennsylvania
between 193 1 and
1940 and who
responded to a
questionnaire in 1962

Reported hours per week of
participation in sports or exercise
in college

Self-reported incidence of
physician-diagnosed
hypertension from mail-
back health questionnaire
(n = 671 I

Paffenbarger et al.
(1983)

Blair et al.
(1984)

Stamler et al.
(1989)

Folsom et al.
(1990)

Paffenbarger et al
(1991)

14,998 US male college
alumni who entered
college between 1916
and 1950; followed
from 1962-l 972
(for 6-l 0 years)

Physical activity index (kcal/week)
estimated from reports of stairs
climbed, city blocks walked, and
sports played each week, assessed
by mail-back questionnaire in
1962 or 1966

4,820 US men and     Maximal aerobic capacity
1,219 US women     estimated by exercise tests,
patients of a preventive  categorized into "high" fitness
medical clinic aged    (2 85th percentile) and "low"
20-65 years at baseline   fitness

201 US men and women  Self-report of moderate physical
with diastolic blood    activity
pressure 85-89 mm Hg
or 80-84 mm Hg (if
overweight) were
randomly assigned to
control or nutritional/
hygienic intervention
(including exercise)

41,837 Iowa women   Self-reported frequency of
aged 55-69 years;    leisure-time physical activity from
2-year follow-up      mail-back survey

5,463 male college
alumni from the
University of
Pennsylvania

Self-report of physical activity from
mail-back questionnaire in 1962

Self-reported incidence of
physician-diagnosed
hypertensjon from mail-
back health questionnaire
(n = 681)

Self-reported incidence
of physician-diagnosed
hypertension (n = 240)

Initiation of hypertensive
therapy or sustained
elevation of diastolic
blood pressure
>90mm Hg

Self-reported incidence of
physician-diagnosed
hypertension

Self-reported incidence of
physician-diagnosed
hypertension from mail-
back questionnaire

in 1976 (n = 739)

108


The Effects of Physical Activity on Health and Disease

Main findings

Dose      Adjustment for confounders
response*    and other comments

Inverse association; respondents who
reported participation in sports or exercise
fewer than 5 hours per week had a
significantly increased age- and interval-
adjusted risk of physician-diagnosed
hypertension (RR = 1.30, p < 0.01)

Inverse association; alumni with
c 2,000 kcal/week of energy expenditure
had RR of 1.30 (95% Cl, 1.09-l .55)
of developing hypertension relative
to others

Patients in low fitness category were 1.52
times as likely (95% Cl, 1.08-2.15) to
develop hypertension as those in high
fitness category

Control group RR = 2.4 (90% Cl, 1.2-4.8)
of developing hypertension when compared
with the intervention group

Inverse association; relative to women
at low levels of physical activity, women
at high and moderate levels had 30% and
10% lower age-adjusted risks of developing
hypertension (RR high = 0.70, 95% Cl,
0.6-0.9; RR moderate = 0.90, 95% Cl,
0.7-l .l)

Vigorous sports play in 1962 was associated
with a 30% reduced risk of developing
hypertension

NA

Adjustments for age and follow-up
had little effect

Yes,
especially
in
heavier

men

Increased risk observed for less active alumni
with stratification of student blood pressure,
alumnus BMI, increase'in BMI since college,
and family history of hypertension

NA

Extensive control for confounding variables;
no sex-specific analyses

NA

Yes

Intervention was combined nutritional,
weight loss, and physical activity

Adjustment for BMI, waist-to-hip ratio,
cigarette smoking, and age eliminated
the association with physical activity

Yes

Adjusted for age, BMI, weight gain
since college, and parental history of
hypertension

Abbreviations: BMI = body mass index (wt [kg] /ht [ml2 ); Cl = confidence interval; RR = relative risk.
`A dose-response relationship requires more than 2 levels of comparison. In this column, "NA" means that there were only
2 levels of comparison; "No" means that there were more than 2 levels but no dose-response gradient was found; "Yes" means
that there were more than 2 levels and a dose-response gradient was found.

109


Physical Activity and Health

controlled trials of habitual activity and blood pres-
sure were analyzed in a meta-analysis by Arroll and
Beaglehole (1992), and nine randomized controlled
trials of aerobic exercise using the lower extremities
(e.g., walking, jogging, cycling) and blood pressure
were analyzed in a meta-analysis by Kelley and
McClellan (1994). The two meta-analyses indepen-
dently concluded that aerobic exercise decreases
both systolic and diastolic blood pressure by ap-
proximately 6-7 mm Hg. Some of the studies were
conducted with persons with defined hypertension
(> 140/90 mm Hg), and others were conducted with
persons with high normal blood pressure. Most of
the studies tested aerobic training of 60-70 percent
maximum oxygen uptake, 3-4 times/week, 30-60
minutes per session,

Three trials have specifically examined the effect
of different intensities of exercise on blood pressure.
Hagberg et al. (1989) randomly assigned 33 hyper-
tensive participants to a nonexercising control group
and to two groups participating in different intensi-
ties of exercise (53 percent and 73 percent of VO,
max) for 9 months. Both exercise groups had compa-
rable decreases in diastolic blood pr,essure (11-12
mm Hg), and the lower-intensity group had a greater
decrease in systolic blood pressure than the higher-
intensity group (20 mm Hg vs. 8 mm Hg). All the
decreases were statistically significant when com-
pared with the control group's blood pressure level,
except the 8 mm Hg decrease in systolic blood
pressure in the higher-intensity group. Matsusaki
and colleagues (1992) randomly assigned 26 mildly
hypertensive participants to two exercise intensities
(50 percent VOLmaxand 75 percent VO,max) for 10
weeks. The pretest-to-posttest decreases in systolic
and diastolic blood pressure in the lower-workload
group were significant (9 mm Hg/6 mm Hg), but
those in the higher-intensity group were not (3 mm
Hg/S mm Hg). Marceau and colleagues (1993) used
a randomized crossover design to compare intensi-
ties of 50 percent and 70 percent `?O,max training on
24-hour ambulatory blood pressure in persons with
hypertension. A similar reduction in 24-hour blood
pressure was observed for both training intensities
(5 mm Hg decrease), but diurnal patterns of reduc-
tion were different.

These trials provide some evidence that moderate-
intensity activity may achieve a similar, or an even

greater, blood-pressure-lowericg effect than
vigorous-intensity activity. Because few studies have
directly addressed the intensity question, however,
the research base is not strong enough to draw a firm
conclusion about the role of activity intensity in
lowering blood pressure. It is not clear, for example,
how the findings could have been affected by several
issues, such as use of antihypertensive medications,
changes in body weight, lack of direct intervention-
control comparisons, dropout rates, and total caloric
expenditure.

Biologic Plausibility

Multiple physiological mechanisms may contribute
to the protective effects of physical activity against
CVDs. Postulated mechanisms involve advantageous
effects on atherosclerosis, plasma lipid/lipoprotein
profile, blood pressure, availability of oxygenated
blood for heart muscle needs (ischemia), blood clot-
ting (thrombosis), and heart rhythm disturbances
(arrhythmias) (Haskell 1995; Leon 1991a; Gordon
and Scott 1991).

Other effects of activity that may be associated
with modifications of CVD risk include reduced
incidence of obesity, healthier distribution of
body fat, and reduced incidence of non-insulin-
dependent diabetes. These other effects are dis-
cussed in later sections of this chapter.

Atherosclerosis

Atherosclerosis begins when cholesterol is trans-
ported from the blood into the artery wall by lipopro-
teins, particularly LDL (Getz 1990; Yanowitz 1992).
The formation of atherosclerotic plaques is increased
at sites where the blood vessel lining is injured,
which may occur in areas where blood flow is uneven
(e.g., near the origin or branching of major vessels).
An inflammatory reaction leads to the formation of
atherosclerotic plaques in the wall of the artery.
In animal studies, exercise has been seen to
protect against the effects of excess cholesterol and
other contributors to the development of athero-
sclerosis (Kramsch et al. 1981). In addition, longi-
tudinal studies of men with coronary artery disease
have shown that endurance training, together with a
cholesterol-lowering diet and interventions for other
CVD risk factors, can help prevent the progression or
reduce the severity ofatherosclerosis in the coronary

110


arteries (Ornish et al. 1990; Schuler et al. 1992;
Hambrecht et al. 1993; Haskell et al. 1994). There is
also an inverse relationship between cardiorespira-
tory fitness and ultrasound-measured severity of
atherosclerosis in neck arteries to the head (carotid
arteries) (Rauramaa et al. 1995).

Plasma Lipid/Lipoprotein Profile
The relationships of physical activity to blood lipid
and lipoprotein levels in men and women have been
reviewed extensively (Leon 1991a; Krummel et al.
1993; Superko 1991; Durstine and Haskell 1994;
Stefanick and Wood 1994). Of more than 60 studies
of men and women, about half found that exercise
training is associated with an increase in HDL. HDL,
a lipid scavenger, helps protect against atherosclero-
sis by transporting cholesterol to the liver for elimi-
nation in the bile (Tall 1990). Cross-sectional studies
show a dose-response relationship between the
amount of regular physical activity and plasma levels
of HDL (Leon 1991c). In these studies, the HDL
levels of endurance-trained male and female athletes
were generally 20 to 30 percent higher than those of
healthy, age-matched, sedentary persons.
Moderate-intensity exercise training appears to
be less likely to increase HDL levels in young to
middle-aged women than men in the same age range
(Leon 1991a; Kummel et al. 1993; Durstine and
Haskelll994). Moderate-intensity exercise was seen
to increase HDL as much as more vigorous exercise
in one randomized controlled trial of women
(Duncan, Gordon, Scott 1991).
  Studies have found that even a single episode of
physical activity can result in an improved blood
lipid profile that persists for several days (Tsopanakis
et al. 1989; Durstine and Haskell 1994). Evidence
also shows that exercise training increases lipopro-
tein lipase activity, an enzyme that removes choles-
terol and fatty acids from the blood (Stefanick and
Wood 1994). Exercise training also reduces elevated
levels of triglycerides (Leon 1991c;. Durstine and
Haskell 1994), another blood lipid associated with
heart disease.

Blood Pressure

The mechanisms by which physical activity low-
ers blood pressure are complicated (Leon 1991a;
American College of Sports Medicine [ACSM]

1993; Fagard et al. 1990) and are mentioned only
briefly here (see also Chapter 3). Blood pressure is
directly proportional to cardiac output and total
resistance in the peripheral blood vessels. An epi-
sode of physical activity has the immediate and
temporary effect of lowering blood pressure through
dilating the peripheral blood vessels, and exercise
training has the ongoing effect of lowering blood
pressure by attenuating sympathetic nervous system
activity (Leon 1991a; ACSM 1993; Fagard et al.
1990). The reduced sympathetic activity may reduce
renin-angiotensin system activity, reset barorecep-
tars: and promote arterial vasodilatation-all of which
help control blood pressure: Improved insulin sensi-
tivity and the associated reduction in circulating
insulin levels may also contribute to blood pressure
reduction by decreasing insulin-mediated sodium
reabsorption by the kidney (Tipton 1984).

lschemia

Clinical symptoms of atherosclerotic CHD occur
when the heart muscle (myocardium) needs more
oxygen than can be supplied from blood flowing
through narrowed coronary arteries. This oxygen
shortage leads to ischemia in the heart muscle-that
is, to inadequate oxygenated blood for myocardial
demand. Adaptations to a gradual reduction in blood
flow may reduce the likelihood of myocardial is-
chemia. For example, new bloodvessels may develop
from other coronary arteries to provide an auxiliary
blood supply (Cohen 1985). A person with advanced
atherosclerotic CHD may remain free of symptoms at
rest but may develop ischemic chest pain (angina
pectoris) or electrocardiographic changes during
physical exertion, which generally result from too
high a myocardial oxygen demand for the blood
supply available through partially occluded coronary
arteries and collateral vessels (Smith and Leon 1992).
Less commonly, angina pectoris may result from
transient constriction (spasm) of a large coronary
artery, generally at the site of an atherosclerotic
plaque, or from spasm of small arterial vessels that
have no evidence of plaque formation.

A recent review has summarized adaptations in
the coronary circulation that are induced by endur-
ance exercise training and that can decrease the
likelihood of ischemia (Laughlin 1994). Data ob-
tained primarily from research on animals have

The Effects of Physical Activity on Health and Disease

111


Physical Activity and Health

demonstrated that exercise leads to a greater capacity
to increase coronary blood flow and an improved
efficiency of oxygen exchange between blood in the
capillaries and the heart muscle cells. These func-
tional changes are the result of a remodeled vascular
structure, improved control of blood flow dynamics,
and promotion of biochemical pathways for oxygen
transfer.

The first and most consistent structural adapta-
tion to exercise is an increase in the interior diameter
of the major coronary arteries and an associated
increase in maximal coronary blood flow (Leon and
Bloor 1968, 1976; Scheuer 1982; Laughlin 1994).
The second vascular adaptation is the formation of
new myocardial blood vessels (capillaries and coro-
nary arterioles) (Tomanek 1994; Leon and Bloor
1968). Animal studies also have shown that exercise
training alters coronary vascular reactivity and
thereby improves control of blood flow and distribu-
tion (Overholser, Laughlin, Bhatte 1994; Underwood,
Laughlin, Sturek 1994). This adaptation may reduce
the incidence of spasms in the proximal coronary
arteries and arterioles (Laughlin 1994). In addition,
exercise training results in a reduced workload on the
heart due to both an increase in compliance of the
heart and a relative reduction in peripheral resistance;
together, these reduce myocardial oxygen demand
(Jorgensen et al. 1977).

Thrombosis

An acute coronary event is usually initiated by dis-
ruption of an atherosclerotic plaque within an artery
(Smith and Leon 1992). Platelet accumulation at the
injury site initiates a cascade of processes leading to
clot formation (thrombosis), which further reduces
or completely obstructs coronary flow. A major
obstruction of flow in a coronary artery may lead to
the death of heart muscle (myocardial infarction) in
the area served by that artery. These obstructions can,
in addition, trigger potentially lethal. disturbances
in the rhythm of the heart (cardiac arrhythmia).

Thrombosis, usually occurring at the site of
rupture or fissuring of an atherosclerotic plaque, is
the precipitating event in the transition of silent or
stable coronary artery disease to acute ischemic
events, such as unstable angina, acute myocardial
infarction, or sudden cardiac death, and in the occur-
rence of ischemic stroke (Davies and Thomas 1985;

Falk 1985). Endurance training reduces thrombosis
by enhancing the enzymatic breakdown of blood
clots (fibrinolysis) and by decreasing platelet adhe-
siveness and aggregation (which helps prevent clot
formation) (Kramsch et al. 1981; Leon 1991b).

Arrhythmia

Although persons with coronary artery disease have
an increased risk of ventricular fibrillation (a life-
threatening heart rhythm disturbance) during acute
physical activity, persons with a healthy cardiovas-
cular system do not incur this elevated risk (Siscovick
et al. 1984; Mittleman et al. 1993; Willich et al. 1993;
Thompson and Mitchell 1984; Thompson, Funk, et
al. 1982; Haskelll995; Dawson, Leon, Taylor 1979).
Exercise training may reduce the risk of ventricular
fibrillation in healthy persons and in cardiac patients
by improving myocardial oxygen supply and de-
mand and by reducing sympathetic nervous system
activity (Leon 199 lc). Evidence from epidemiologic
studies shows that a physically active lifestyle re-
duces the risk of sudden cardiac death (Leon et al.
1987). A meta-analysis of studies that examined use
of physical activity for cardiac rehabilitation showed
that endurance exercise training reduced the overall
risk of sudden cardiac death even among persons
with advanced coronary atherosclerosis (O'Connor
et al. 1989).

Conclusions

The epidemiologic literature supports an inverse
association and a dose-response gradient between
physical activity level or cardiorespiratory fitness
and both CVD in general and CHD in particular. A
smaller body of research supports similar findings
for hypertension. The biological mechanisms for
these effects are plausible and supported by a wealth
of clinical and observational studies. It is unclear
whether physical activity plays a protective role
against stroke.

Cancer

Cancer, the second leading cause of death in the
United States, accounts for about 25 percent of all
deaths, and this percentage is increasing (NCHS
1996; American Cancer Society [ACS] 1996). The
ACS has estimated that 1,359,150 new cases of

112


The Effects of Physical Activity on Health and Disease

cancer and 554,740 cancer-related deaths will occur
amongAmericansduring 1996 (ACS 1996). Physical
inactivity has been examined as an etiologic factor
for some cancers.

Colorectal Cancer

Colorectal cancer has been the most thoroughly
investigated cancer in epidemiologic studies of physi-
cal activity. To date, nearly 30 published studies have
examined the association between physical activity
and risk of developing colon cancer alone.
  Studies that combined colon and rectal cancers
as a single endpoint-colorectal cancer-are only
briefly reviewed here because current research, sum-
marized in this section, suggests that the relation-
ship between physical activity and risk of colon
cancer may be different from that for rectal cancer.
Among nine studies that have examined the relation-
ship between physical activity and colorectal cancer,
one reported an inverse relationship (Wu et al.
1987), and three reported positive associations that
were not statistically significant (Garfinkel and
Stellman 1988; Paffenbarger, Hyde, Wing 1987 [for
analysis of two cohorts] ). One (Kune, Kune, Watson
1990) reported no significant associations, and in
the four other studies (Albanes, Blair, Taylor 1989;
Ballard-Barbash et al. 1990; Markowitz et al. 1992;
Peters et al. 1989), the associations lacked consis-
tency in subpopulations within the study, anatomic
subsites of the large bowel, or measures of physical
activity. Colorectal adenomas are generally thought
to be precursors to colorectal cancers. A single study
of colorectal adenomatous polyps has reported an
inverse relationship between risk of adenomas and
level of total physical activity (Sandler, Pritchard,
Bangdiwala 1995). Another study of colorectal ad-
enomas also found an inverse association, but only
for running or bicycling, and only with one of two
different comparison groups (Little et al. 1993).

Colon Cancer

Of the 29 studies of colon cancer,.18 used job title as
the only measure of physical activity and thus ad-
dressed only occupational physical activity. These
studies are a mix of mortality and incidence studies,
and few have evaluated possible confounding by
socioeconomic status, diet, and other possible risk
factors for colon cancer. Nonetheless, findings from

these 18 studies have been remarkably consistent: 14
studies (Brownson et al. 1989; Brownson et al. 1991;
Chow et al. 1993; Dosemeci et al. 1993; Fraser and
Pearce 1993; Fredriksson, Bengtsson, Hardelll989;
Garabrant et al. 1984; Gerhardsson et al. 1986; Kato,
Tominaga, Ikari 1990; Lynge and Thygesen 1988;
Marti and Minder 1989; Peters et al. 1989; Vena et al.
1985; Vena et al. 1987) reported a statistically sig-
nificant inverse relationship between estimated oc-
cupational physical activity and risk of colon cancer.
Four studies (Arbman et al. 1993; Vetter et al. 1992;
Vlajinac, Jarebinski, Adanja 1987; Vineis, Ciccone,
Magnino 1993) found no significant relationship
between occupational physical activity and risk of
colon cancer. The 18 studies were conducted in a
variety of study populations in China, Denmark,
Japan, New Zealand, Sweden, Switzerland, Turkey,
and the United States.

  Eleven studies assessed the association be-
tween leisure-time or total physical activity and
colon cancer risk in 13 different study populations
(Table 4-5). These studies either measured physical
activity and tracked participants over time to ascer-
tain colon cancer outcomes or compared recalled
histories of physical activity among colon cancer
patients with those among controls. In eight study
populations, an inverse association was reported
between physical activity and risk of colon cancer,
and results were generally consistent for men and
women. The three studies that examined the effect of
physical activity during early adulthood (Polednak
1976; Paffenbarger, Hyde, Wing 1987; Marcus,
Newcomb, Storer 1994) found no effect, which could
indicate that the earlier activity did not affect risk of
colon cancer later in life. In studies that used more
than two categories of physical activity, 10 potential
dose-response relationships between level of physi-
cal activity or cardiorespiratory fitness and colon
cancer risk were evaluated. Five of these showed a
statistically significant inverse dose-response gradi-
ent, one showed an inverse dose-response gradient
that was not statistically significant, three showed no
gradient, and one showed a positive relationship that
was not statistically significant.

Two studies of colon adenomas (Giovannucci
et al. 1995; Kono et al. 1991) reported an inverse
relationship between leisure-time physical activity
and risk of colon adenomas.

113


Physical Activity and Health

Table 4-5.  Epidemiologic studies of leisure-time or leisure-time plus occupational physical activity*
       and colon cancer

Study

Population

Definition of
physical activity

Definition of

cancer

Polednak       Cohort of 8,393 former
(1976)        US college men

Paffenbarger,
Hyde, Wing
(1987)

Cohort of 51,977 male,
4,706 female former US
college students

Gerhardsson,
Floderus,
Norell
(1988)

Slattery et al.
(1988)

Severson et al.
(1989)

Gerhardsson
et al.
(1990)

Whittemore et al.
(1990)

Lee,
Paffenbarger,
Hsieh
(1991)

Cohort of 16,936 male
US college alumni
aged 35-74 years

Cohort of 16,477
Swedish men and
women twins aged
43-82 years
Cohort of Utah men
(110 cases and
180 controls) and
women (119 cases
and 204 controls)
aged 40-79 years

Cohort of 7,925
Japanese men
aged 46-65 years

Swedish men (163
cases) and women
(189 cases) and 5 12
controls; all ages

North American
Chinese men
(179 cases and 698
controls) and women
(114 cases and 494
controls) aged
2 20 years

Asian Chinese men
(95 cases and 678 *
controls) and women
(78 cases and 618
controls) aged
20-79 years

Cohort of 7,148 male
male US college alumni
aged 30-79 years

College athletic status; major,
minor, and nonathlete
Sports play in college

Physical activity index (kcal/week)

Categories of occupational and
leisure-time activity

Occupational and leisure-time
activity were both assessed by
total energy expended

Physical activity index from
Framingham study and heart rate

Categories of occupational and
leisure-time activity

Time per day spent sleeping/
reclining, sitting, in light or
moderate activity, and in
vigorous activity

Time per day spent sleeping
reclining, sitting, in light or
moderate activity, and in
vigorous activity

Index of energy expenditure based
on stair climbing, walking, and
sports/recreation, assessed 2 times

Colon cancer mortality
(n = 107)

Colon cancer incidence
(n = 201)

Colon cancer mortality
(n = 44) ,

Colon cancer incidence

Colon cancer incidence

Colon cancer incidence
(n = 172)

Colon cancer incidence

Colon cancer incidence

Colon cancer incidence

Colon cancer incidence

> 11 years apart

114


The Effects of Physical Activity on Health and Disease

Main findings

Dose    Adjustment for confounders
response+  and other comments

No differences in mortality                No

Sports play 15 hrs/week relative to
< 5 hrs/week: RR = 0.91; p = 0.60

NA

Risk increased with physical activity index:
p for trend = 0.45

No

Least active relative to most active for work
and leisure: RR = 3.6 (95% Cl, 1.3-9.8)

NA

High activity quartile relative to low
activity quartile; men: OR total 0.70
(90% Cl, 0.38-l .29); women: OR total 0.48
(90% Cl, 0.27-0.87)

High activity tertile relative to low activity
tertile: RR 0.71 (95% Cl, 0.51-0.99); high
heart rate relative to low: RR 1.37
(95% Cl, 0.97-l .93)

Low activity relative to high: work and leisure,
RR = 1.8 (95% Cl, 1 .O-3.4)

Sedentary relative to active:
RR = 1.6 (95% Cl, 1 .l-2.4) for men,
RR = 2.0(95% Cl, 1.2-3.3) for women

Sedentary relative to active:
RR = 0.85 (95% Cl, 0.39-l .V) for men,
RR = 2.5 (95% Cl, 1 .O-6.3) for wemen

Highly active relative to inactive:
RR = 0.85 (90% Cl, 0.6-l .l);
high lifetime activity:
RR = 0.5 (90% Cl, 0.3-0.9)

Yes

No

Yes

Yes

NA

NA

No

None

Adjusted for age (2 levels of activity)

Adjusted for age, BMI, and smoking

Adjusted for age and sex (2 levels of lag ttvity);
adjustments for possible confounders 5,1t,t
to not change results

Adjusted for age, BMI, dietary fiber, allIt total
energyintake; greater effect with inten\,;
activity; population-based

Adjusted for age, BMI

Adjusted for age, sex, BMI, dietary int.ll.,,
of total energy, protein, fat, fiber, and
browned meat surface; population-b,r>,.,t

Adjusted for age (2 levels of activity);
population-based; adjustment for diet l,.,d little
effect on findings

Adjusted for age (2 levels of activity);
population-based; no effect of physic -11
activity after adjustment for diet

Adjusted for age

115


Physical Activity and Health

Table 4-5. Continued

                          Definition of              Definition of
Study       Population       physical activity                  cancer

Marcus,         Wisconsin women    Total strenuous physical activity    Colon cancer incidence
Newcomb,     aged up to 74 years,    during ages 14-22 years
Storer          536 cases and
(1994)        2,315 controls

Giovannucci et al.  47,723 US male health   Weekly recreational physical     Colon cancer incidence
(1995)        professionals aged     activity index based on 8        (n = 201)
           40-75 years       categories of moderate and
                      vigorous activities
Longnecker et al.   US men aged > 30    Leisure-time vigorous physical    Right-Gded colon cancer
(1995)        years, 163 cases      activity                   incidence
            703 controls

Dietary factors may confound or modify the
association between physical activity and colon
cancer risk (Willett et al. 1990). Five of the studies
in Table 4-5 controlled for dietary components in
analyses and continued to observe a significant
inverse association (Gerhardsson, Floderus, Norell
1988; Slattery et al. 1988; Gerhardsson et al. 1990;
Giovannucci et al. 1995; Longnecker et al. 1995),
and in one study (Whittemore et a1.1990), adjust-
ment for dietary intakes altered findings in one
study population but not in the other.
Together, the research on occupational and
leisure-time or total physical activity strongly sug-
gests that physical activity has a protective effect
against the risk of developing colon cancer.

Rectal Cancer

Many of the studies on physical activity and colon
cancer risk also studied rectal cancer as a separate
outcome. Of 13 studies that investigated occupa-
tional physical activity alone, 10 reported no statis-
tically significant association with rectal cancer risk
(Garabrant et al. 1984; Vena et al: 1985, 1987;
Gerhardsson et al. 1986; Jarebinski, Adanja, Vlajinac
1988; Lynge and Thygesen 1988; Brownson et al.
1991; Marti and Minder 1989; Peters et al. 1989;
Dosemeci et al. 1993), two reported significant in-
verse associations (Kate, Tominaga, Ikari 1990; Fraser
and Pearce 1993), and one reported a significant

direct association (i.e., increasing risk with increas-
ing physical activity) (Arbman et al. 1993).
Six of the studies that investigated the associa-
tion between leisure-time or total physical activity
and the risk of developing rectal cancer failed to
find a significant association (Gerhardsson,
Floderus, Norell 1988; Severson et al. 1989;
Gerhardsson et al. 1990; Kune, Kune, Watson 1990;
Lee, Paffenbarger, Hsieh 1991; Longnecker et al.
1995). In another study, Whittemore and colleagues
(1990) observed a statistically significant inverse
association in one study population and no effect in
the other. Paffenbarger, Hyde, and Wing (1987)
found an inverse relationship in one cohort and a
direct relationship in the other.
Taken together, study results on both occupa-
tional and leisure-time or total physical activity
suggest that risk of rectal cancer is unrelated to
physical activity.

Hormone-Dependent Cancers in Women
Of the epidemiologic studies examining the relation-
ship between physical activity and hormone-
dependent cancers in women, 13 have investigated
the risk associated with breast cancer, two with
ovarian cancer, four with uterine corpus cancer
(mostly endometrial), and one with a combination of
cancers. It should be noted that studies of physical
activity in women have been especially prone to
misclassification problems because they did not

116


The Effects of Physical Activity on Health and Disease

Main findings
Any strenuous activity relative to none:
RR = 1 .O (95% Cl, 0.8-l .3)

Dose    Adjustment for confounders
response+   and other comments

No     Adjusted for age, family history, screening
     sigmoidoscopy, BMI; population based

Most active quintile compared with least
active quintile, RR = 0.53 (95% Cl,
0.32-0.88) p for trend = 0.03

Yes

Adjusted for age, BMI, parental history of
colorectal cancer, history of endoscopic
screening or polyp diagnosis, smoking,
aspirin use, and diet

Vigorous activity > 2 hours/week relative
to none: RR = 0.6 (95% Cl, 0.4-l .O)

Yes

Adjusted for BMI, fahily history, income,
race, smoking, and intakes of alcohol, energy,
fat, fiber, and calcium

Abbreviations: BMI = body mass index (wt [kg] /ht [ml' ); Cl = confidence interval; OR = odds ratio; RR = relative risk.
`Excludes studies where only occupational physical activity was measured.
`A dose-response relationship requires more than 2 levels of comparison. In this column, "NA" means that there were only 2 levels of
comparison; "No" means that there were more than 2 levels but no dose-response gradient was found; "Yes" means that there were
more than 2 levels and a dose-response gradient was found.

include household work and child care in their
assessment. Studies of leisure-time or total physical
activity and hormone-dependent cancers in women
are summarized in Table 4-6.

Breast Cancer

Four of the 13 breast cancer studies considered only
occupational physical activity. Two of those studies
described significant inverse associations (Vena et
al. 1987; Zheng et al. 1993), and two others reported
no significant association (Dosemeci et al. 1993;
Pukkala etal. 1993). Only two (Dosemecietal. 1993;
Pukkala et al. 1993) adjusted for socioeconomic
status, and none gathered information about repro-
ductive factors and thus could not control for those
potential confounding variables.

The epidemiologic studies of leisure-time or
total physical activity and breast cancer risk have
yielded inconsistent results (Table 4:6). Of these 10
studies, two reported a significant inverse associa-
tion (Bernstein et al. 1994; Mittendorf et al. 1995),
three reported an inverse association that was not
statistically significant (Frisch et al. 1985,1987;
Friedenreich and Rohan 1995), three reported no
relationship (Paffenbarger, Hyde, Wing 1987;
Albanes, Blair, Taylor 1989; Taioli, Barone, Wynder
1995). The other two reported a direct association,

although in one this did not reach statistical signifi-
cance (Dorgan et al. 1994), and in the other it
remained statistically significant (after adjustment
for confounding) only for physical activity at age 30-
39 years (Sternfeld et al. 1993).

Even among the studies that controlled for po-
tential confounding by reproductive factors, find-
ings were inconsistent (Bernstein et al. 1994; Dorgan
et al. 1994; Sternfeld et al. 1993; Friedenreich and
Rohan 1995; Mittendorf et al. 1995; Taioli, Barone,
Wynder 1995). Results were inconsistent as well
among studies that included primarily postmeno-
pausal women (i.e., all but the study by Bernstein and
colleagues [ 19941).

Nonetheless, it is possible that physical activ-
ity during adolescence and young adulthood may
protect against later development of breast cancer.
Five of the studies cited here have examined this
possibility. Among these five studies, two found a
strong and statistically significant reduction in
risk (Bernstein et al. 1994 [RR = 0.421; Mittendorf
et al. 1995 [RR = 0.5]), one found a nonsignificant
reduction in risk (Frisch et al. 1985 [RR = 0.54]),
and two found a null association (Paffenbarger,
Hyde, Wing 1987; Taioli, Barone, Wynder 1995).
These studies thus lend limited support to the hy-
pothesis that physical activity during adolescence

117


Physical Activity and Health

Table 4-6.  Epidemiologic studies of leisure-time or leisure-time plus occupational physical activity*
     and hormone-dependent cancers in women

                           Definition of              Definition of

Study

Population

physical activity

cancer

Breast cancer

Frisch et al.
(1985 and 1987)

Paffenbarger,
Hyde, Wing
(1987)
Albanes, Blair,
Taylor (1989)

Sternfeld et al.
(1993)

Bernstein et al.
(1994)

Dorgan et al.
(1994)

Friedenreich and
Rohan (1995)

Mittendorf et al.
(1995)

Taioli, Barone,    All ages in US; 617
Wynder (1995)    cases; 531 controls

Ovarian cancers

Mink et al. (1996)

Iowa Women's
Health Study; cohort
of 3 1,396 postmeno-
pausal women

Cohort of former US
college athletes and
nonathletes; 5,398
women aged 2 l-80
years

Cohort of former US
college students,
4,706 women

NHANES cohort: 7,413
women aged 25-74
years, in US

254 cases and 201
controls in an HMO

Women 2 40 years; 545
cases and 545 controls
in California, US

Framingham Study
cohort: 2,307 women
aged 35-68 years,
Massachusetts, US

Australian women
aged 20-74 years;
451 cases and 451
controls (matched)

US women aged
17-74 years; 6,888
cases and 9,539
controls

Athletic status during college

Sports play during college

One question on nonrecreational
activity, one on recreational
activity

Age-specific recreational activity
levels

Participation in several leisure-
time activities after menarche

Physical activity index

Recreational physical activity
index

Strenuous physical activity at
ages 14-22 years

Leisure-time physical activity at
ages 15-22 years

Categories of physical activity

Breast cancer prevalence
(n = 69)

Breast cancer incidence
and mortality

Breast cancer incidence
(n = 122)

Breast cancer incidence

Breast cancer incidence
in situ and invasive

Breast cancer incidence
(n = 117)

Breast cancer incidence

Breast cancer incidence

Breast cancer incidence

Ovarian cancer incidence
(n = 97)

118


The Effects of Physical Activity on Health and Disease

Main findings

Dose
response+

Adjustment for confounders
and other comments

Nonathletes vs. athletes:
RR = 1.86 (95% Cl, 1 .O-3.47)

Sports play of 2 5 relative to < 5 hours/week
RR = 0.96 (p value = 0.92)

Sedentary relative to most active: RR = 1 .l
(95% Cl, 0.6-2.0) for nonrecreational;
RR = 1 .O (95% Cl, 0.6-l .6) for recreational

For activity from age 30-39, high activity
quartile vs. low activity quartile, postmeno-
pausal OR = 2.3 (95% Cl, 1.03-5.04); pre-
menopausal OR = 2.8 (95% Cl, 0.98-5.18)

2 3.8 hours/week relative to 0 hours
of leisure-time activity, RR = 0.42
(95% Cl, 0.27-0.64)

High activity quartile relative to low activity
quartile: RR = 1.6 (95% Cl, 0.9-2.9)

> 4,000 kcal/week in physical activity
relative to none: RR = 0.73
(95% Cl, 0.51-l .05)

1 daily strenuous activity relative
to none: RR = 0.5 (95% Cl, 0.4-0.7)

> 1,750 kcal/week relative to none:
RR = 1.1 (95% Cl, 0.5-2.6)     .

Most active relative to least active:
RR = 1.97 (95% Cl, 1.22-3.19)

NA

Adjusted for age, family history of cancer,
age at menarche, number of pregnancies,
oral contraceptive use, smoking,
use of estrogen, leanness

NA      Adjusted for age

No

Adjusted for age; adjustment for confounders
had little effect on results; suggestive of variable
effects by menopausal status

Yes
(opposite
direction)

Adjusted for age, menopausal status, and
potential confounders

Yes

Adjusted for age, race, neighborhood, age at
menarche, age at first full-term pregnancy,
number of full-term pregnancies, oral
contraceptive use, lactation, family history of
breast cancer, Quetelet index; population-based

Yes
(opposite
direction)

Adjusted for age, menopausal status, age at
first pregnancy, parity, education, occupation,
and alcohol

Yes

Adjusted for BMI and energy intake;
effects observed for premenopausal and
postmenopausal cancer and for light and
vigorous activity; population-based

Yes

Adjusted for age, parity, age at first birth, family
history, BMI, prior breast disease, age at
menopause, menopausal status, alcohol use,
and menopausal status x BMI; population-based

No

Adjusted for age, education, BMI, age at
menarche, and prior pregnancy; hospital-based

Yes
(opposite
direction)

Adjusted for age, smoking, education, live births,
hysterectomy, and family history

119


Physical Activity and Health

Table 4-6. Confirmed

                           Definition of              Definition of
Study        Population       physical activity                   cancer

Endometrial cancers

Levi et al.
(1993)

Shu et al.
(1993)

Sturgeon et al.
(1993)

Combined set

Frisch et al.
(1985 and 1987)

Switzerland/Northern   Categories of leisure-time and
Italy; 274 cases and 572  occupational activity
controls aged 31-75

Women in Shanghai,
China aged 18-74
years, 268 cases
and 268 controls

Occupational and nonoccupa-     Endometrial cancer
tional physical activity index      incidence

US women aged
20-74 years;
405 cases
and 297 controls

Recreational and nonrecreational
activity categories

Cohort of former US
college athletes and
nonathletes; 5,398
women aged 2 l-80
years

Athletic status during college

Endometrial cancer
incidence

Endometrial cancer
incidence

Cervix, uterus, ovary,
vagina cancer prevalence
(n = 37)

and young adulthood may be protective against later
development of breast cancer.

Other Hormone-Dependent Cancers in Women
Too little information is available to evaluate the
possible effect of physical activity on risk of ovarian
cancer. Zheng and colleagues (1993) found no sig-
nificant associations between occupational physical
activity and risk of ovarian cancer. On the other
hand, data from the Iowa Women's Health Study
showed that risk of ovarian cancer among women
who were most active was twice the risk among
sedentary women (Mink et al. 1996).   '
Findings are limited for uterine corpus cancers as

well. Zheng et al. (1993) found no relationship
between physical activity and risk of cancer of the
uterine corpus. Among the endometrial cancer stud-
ies, one (Levi et al: 1993) found a decreased risk
associated with nonoccupational activity, and one
(Sturgeon et al. 1993) found combined recreational

and nonrecreational activity to be protective. An-
other study (Shu et al. 1993) found no protective
effect of nonoccupational activity in any age group
and a possible protective effect of occupational activ-
ity among younger women but not among older
women.

In Frisch and colleagues' (1985) study of the
combined prevalence of cancers of the ovary, uterus,
cervix, and vagina, nonathletes were 2.5 times more
likely than former college athletes to have these
forms of cancer at follow-up. Because these cancers
have different etiologies, however, the import of this
finding is difficult to determine.

Thus the data are either too limited or too
inconsistent to firmly establish relationships be-
tween physical activity and hormone-dependent can-
cers in women. The suggestive finding that physical
activity in adolescence and early adulthood may
protect against later development of breast cancer
deserves further study.

120


The Effects of Physical Activity on Health and Disease

Main findings

Dose
response+  Adjustment for confounders
       and other comments

Sedentary relative to active for total activity:
RR = 2.4 (95% Cl, 1 .O-5.8) to RR = 8.4
(95% Cl, 3.0-25.3) for different ages

LOW average adult activity quartile relative
to high quartile: occupational age I 55 years
RR = 2.5 (95% Cl, 0.9-6.3), age > 55 years
RR = 0.6 (no Cl given); nonoccupational
RR = 0.8 (95% Cl, 0.5-l .3)

Sustained (lifetime) activity, inactive
relative to active: recreational RR = 1.5
(95% Cl, 0.7-3.2) nonrecreational RR = 1.6
(95% Cl, 0.7-3.3)

Nonathletes vs. athletes:
RR = 2.53 (95% Cl, 1 .17-5.47)

Yes

Adjusted for age, education, parity,
menopausal status, oral contraceptive use,
estrogen replacement, BMI, and caloric intake;
hospital-based

No

Adjusted for age, number of pregnancies,
BMI, and caloric intake; possible modification
of occupational activity by age;
population-based *

No

Adjusted for age, study area, education, parity,
oral contraceptive use, hormone replacement
use, cigarette smoking, BMI, and other type of
activity; recent activity also protective;
population-based

N/A

Adjusted for age, family history of cancer,
age at menarche, number of pregnancies,
oral contraceptive use, smoking, use of
estrogen, leanness

Abbreviations: BMI = body mass index (wt [kg]/ht [ml> ); Cl = confidence interval; HMO = health maintenance organization;
NHANES = National Health and Examination Survey; OR = odds ratio; RR = relative risk.
`Excludes studies where only occupational physical activity was measured.
`A dose-response relationship requires more than 2 levels of comparison. In this column, "NA" means that there were only 2 levels of
comparison; "No" means that there were more than 2 levels but no dose-response gradient was found; "Yes" means that there were
more than 2 levels and a dose-response gradient was found.

Cancers in Men

Prostate Cancer

Among epidemiologic studies of physical activity
and cancer, prostate cancer is the second most com-
monly studied, after colorectal cancer. Results of
these studies are inconsistent. Seven studies have
investigated the association between occupational
physical activity and prostate cancer risk or mortal-
ity. Two described significant inverse dose-response
relationships (Vena et al. 1987; Brownson et al.
199 1). Two showed a nonsignificant decreased risk
with heavy occupational activity (Dosemeci et al.
1993; Thune and Lund 1994). In one publication
that presented data from two cohorts, there was no
effect in either (Paffenbarger, Hyde, Wing 1987).

The remaining study (Le Marchand, Kolonel,
Yoshizawa 1991) reported inconsistent findings by
age: increasing risk with increasing activity among
men aged 70 years or older and no relationship
among men younger than age 70.
The 10 studies of leisure-time physical activity,
or total physical activity, or cardiorespiratory fitness
and risk of prostate cancer have also produced
inconsistent results (Table 4-7). Two of the studies
described significant inverse relationships (Lee,
Paffenbarger, Hsieh 1992; Oliveria et al. 1996),
although one of these (Lee, Paffenbarger, Hsieh
1992) observed this relationship only among men
aged 70 years or older. Four studies found inverse
relationships (Albanes, Blair, Taylor 1989; Severson
et al. 1989; Yu, Harris, Wynder 1988; Thune and

121


Physical Activity and Health

Table 4-7. Epidemiologic studies of leisure-time or total physical activity or cardiorespiratory fitness and
     prostate cancer
                   Definition of physical activity     Definition of
Study       Population       or cardiorespiratory fitness          cancer

Physical activity
Polednak (1976)

Paffenbarger,
Hyde, Wing
(1987)

Yu, Harris,
Wynder
(1988)

Albanes, Blair,
Taylor (1989)

Severson et al.
(1989)

West et al. (1991)

Lee, Paffenbarger,
Hsieh (1992)

Thune and Lund
(1994)

Cohort of 8,393 former
US college men

Cohort of 51,977
US male former
college students
16,936 US male alumni
aged 35-74 years

US men, all ages,
1,162 cases and
3,124 controls

NHANES cohort of
5,141 US men aged
25-74 years

Cohort of 7,925
Japanese men
in Hawaii aged
46-65 years

Utah men aged 45-74
years, 358 cases
and 679 controls

Cohort of US college
alumni, 17,719 men
aged 30-79 years

Cohort of Norwegian
43,685 men

Cardiorespiratory Fitness
Oliveria et al.     Cohort of 12,975
(1996)         Texas men
         aged 20-80 years

Cohort of 7,570
Texas men

College athletic status, major,
minor, and nonathletes
Sports play

Physical activity index

Categories of leisure-time
aerobic exercise

Categories of recreational and
nonrecreational activity

Physical activity index from
Framingham study and heart rate

Categories of energy expended

Physical activity index based on
stair climbing, walking, playing
sports

Recreational and occupational
activity based on questionnaire;
categories of occupational and
leisure-time activity

Maximal exercise test

Categories of weekly energy
expenditure in leisure time

Prostate cancer incidence
(n = 124)

Prostate cancer incidence
and mortality (n = 154 1

Prostate cancer mortality
(n = 36) '
Prostate cancer incidence

Prostate cancer incidence

Prostate cancer incidence

Prostate cancer incidence

Prostate cancer incidence
(n = 221)

Prostate cancer incidence
(n = 220)

Prostate cancer incidence
or mortality (n = 94)

Prostate cancer incidence
or mortality (n = 44)

122


The Effects of Physical Activity on Health and Disease

Main findings

Dose    Adjustment for confounders
response*  and other comments
    -

Major athletes relative to nonathletes,
RR = 1.64 (p < 0.05)
Sports play 2 5 relative to < 5 hours/week,
RR = 1.66; (p < 0.05)

No

None

NA

Adjusted for age (2 levels of activity)

Comparing 2 2,000 with < 500 kcal/week,
RR = 0.57; p = 0.33

No

Adjusted for age, BMI, and smoking

Most sedentary relative to most active
menduring leisure time,
RR = 1.3 (95% Cl, 1.0-l .6) for whites,
RR = 1.4 (95% Cl, 0.8-2.6) for blacks

Yes

Adjusted for age; in multivariate analysis,
findings no longer significant for whites;
hospital based

Least active relative to most               Adjusted for age; further adjustment for
active individuals,                      confounders said to not affect results

RR = 1.3 (95% Cl, 0.7-2.4);
for nonrecreational
RR = 1.8 (95% Cl, 1 .O-3.3);
for recreational

RR = 1.8 (95% Cl, 1 .O-3.3)
Most active relative to least active men,
RR = 1.05 (95% Cl, 0.73-l .51);
for occupation,
RR = 0.77 (95% Cl, 0.58-l .Ol );
high heart rate relative to low,
RR = 0.97 (95% Cl, 0.69-l .36)

Overall no association found

No


Ye5


No

Adjusted for age, BMI

NA


No


NA

Men aged 2 70 years: comparing > 4,000
with c 1,000 kcal/week; RR = 0.53
(95% Cl, 0.29-0.95); men aged < 70 years,
RR = 1.21 (95% Cl, 0.8-0.18)

No

For agressive tumors, physical activity was
associated with increased risk, but this was
not statistically significant
Adjusted for age; no effect of activity at
2,500 kcal, the level found protective
for colon cancer

Heavy occupational activity relative to
sedentary, RR = 0.81 (95% Cl, 0.50-l .30);
regular training in leisure time relative to
sedentary, RR = 0.87 (95% Cl, 0.57-l .34)

No

Adjusted for age, BMI, and geographic region

Among men < 60 years, most fit relative to
least fit, RR = 0.26 (95% Cl, 0.1 o-0.63);
among men > 60 years, no effect, RR not given

13,000 kcal/week relative to < 1,000
kcal/week, RR = 0.37 (95% Cl, 0.14-0.98)

Yes

No


No

Adjusted for age, BMI, and smoking

Adjusted for age, BMI, and smoking

Adjusted for age, BMI, and smoking

Abbreviations: BMI = body mass index (wt (kg]/ht [ml* ); Cl = confidence interval; RR = relative risk.
`A dose-response relationship requires more than 2 levels of comparison. In this column, "NA" means that there were only 2 levels of
comparison; "No" means that there were more than 2 levels but no dose-response gradient was found; "Yes" means that there were more
than 2 levels and a dose-response gradient was found.

123


Physical Activity and Health

Lund 1994), but these were not statistically signifi-
cant, and one of the four (Thune and Lund 1994)
showed this relationship only for those aged 60 years
or older. Two studies found that men who had been
athletically active in college had significantly in-
creased risks of later developing prostate cancer
(Polednak 1976; Paffenbarger, Hyde, Wing 1987).
One study found no overall association between
physical activity and prostate cancer risk but found
a higher risk (although not statistically significant)
of more aggressive prostate cancer (West et al. 1991).

The two studies of the association of cardiorespi-
ratory fitness with prostate cancer incidence were
also inconsistent. Severson and colleagues (1989)
found no association between resting pulse rate and
subsequent risk of prostate cancer. Oliveria and col-
leagues (1996) found a strong inverse dose-response
relationship between fitness assessed by time on a
treadmill and subsequent risk of prostate cancer.

Thus the body of research conducted to date
shows no consistent relationship between prostate
cancer and physical activity.

Testicular Cancer

Two studies investigated physical activity and risk of
developing testicular cancer; again, results are in-
consistent. A case-control study in England found
that men who spent at least 15 hours per week in
recreational physical activity had approximately half
the risk of sedentary men, and a significant trend was
reported over six categories of total time spent exer-
cising (United Kingdom Testicular Cancer Study
Group 1994). A cohort study in Norway (Thune and
Lund 1994) was limited by few cases. It showed no
association between leisure-time physical activity
and risk of testicular cancer, but heavy manual
occupational activity was associated with an ap-
proximately twofold increase in risk, although this
result was not statistically significant. Thus no mean-
ingful conclusions about a relationship between
physical activity and testicular cancer can be drawn.

Other Site-Specific Cancers
Few.epidemiologic studies have examined the asso-
ciation of physical activity with other site-specific
cancers (Lee 1994). The totality of evidence provides
little basis for a suggestion of a relationship.

Biologic Plausibility

Because the data presented in this section demon-
strate a clear association only between physical ac-
tivity and colon cancer, the biologic plausibility of
this relationship is the focus of this section. The
alteration of local prostaglandin synthesis may serve
as a mechanism through which physical activity may
confer protection against colon cancer (Shephard et
al. 1991; Lee 1994; Cordain, Latin, Beanke 1986).
Strenuous physical activity increases prostaglandin
F, alpha, which strongly increases intestinal motil-
ity, and may suppress prostaglandin E,, which re-
duces intestinal motility and, released in greater
quantities by colon tumor cells than normal cells,
accelerates the rate of colon cell proliferation (Thor
et al. 1985; Tutton and Barkla 1980). It has been
hypothesized that physical activity decreases gas-
trointestinal transit time, which in turn decreases
the length of contact between the colon mucosa and
potential carcinogens, cocarcinogens, or promoters
contained in the fecal stream (Shephard 1993; Lee
1994). This hypothesis could partly explain why
physical activity has been associated with reduced
cancer risk in the colon but not in the rectum.
Physical activity may shorten transit time within
segments of the colon without affecting transit time
in the rectum. Further, the rectum is only intermit-
tently filled with fecal material before evacuation.
Despite these hypothetical mechanisms, studies on
the effects of physical activity on gastrointestinal
transit time in humans have yielded inconsistent
results (Shephard 1993; Lee 1994).

Conclusions

The relative consistency of findings in epidemio-
logic studies indicates that physical activity is asso-
ciated with a reduced risk of colon cancer, and
biologically plausible mechanisms underlying this
association have been described. The data consis-
tently show no association between physical activ-
ity and rectal cancer. Data regarding a relationship
between physical activity and breast, endometrial,
ovarian, prostate, and testicular cancers are too
limited or too inconsistent to support any firm
conclusions. The suggestion that physical activity
in adolescence and early adulthood may protect
against later development of breast cancer clearly
deserves further study.

124


The Effects of Physical Activity on Health and Disease

Non-Insulin-Dependent
Diabetes Mellitus

An estimated 8 million Americans (about 3 percent of
the U.S. population) have been diagnosed with diabe-
tes mellitus, and it is estimated that twice that many
have diabetes but do not know it (Harris 1995). More
than 169,000 deaths per year are attributed to diabetes
as the underlying cause, making it the seventh leading
cause of mortality in the United States (NCHS 1994).
This figure, however, underestimates the actual death
toll: in 1993, more than twice this number of deaths
occurred among persons for whom diabetes was listed
as a secondary diagnosis on the death certificate.
Many of these deaths were the result of complications
of diabetes, particularly CVDs, including CHD, stroke,
peripheral vascular disease, and congestive heart fail-
ure. Diabetes accounts for at least 10 percent of all
acute hospital days and in 1992 accounted for an
estimated $92 billion in direct and indirect medical
costs (Rubin et al. 1993). In addition, by age 65 years,
about 40 percent of the general population has im-
paired glucose tolerance, which increases the risk of
CVD (Harris et al. 1987).

Diabetes is a heterogeneous group of metabolic
disorders that have in common elevated blood glucose
and associated metabolic derangements. Insulin-
dependent diabetes mellitus (IDDM, or type I) is
characterized by an absolute deficiency of circulat-
ing insulin caused by destruction of pancreatic beta
islet cells, thought to have occurred by an auto-
immune process. Non-insulin-dependent diabetes
mellitus (NIDDM, or type II) is characterized either
by elevated insulin levels that are ineffective in
normalizing blood glucose levels because of insulin
resistance (decreased sensitivity to insulin), largely
in skeletal muscle, or by impaired insulin secretion.
More than 90 percent of persons with diabetes have
NIDDM (Krall and Beaser 1989).

Nonmodifiable biologic factors implicated in the
etiology of NIDDM include a strong genetic influence
and advanced age, but the development of insulin
resistance, hyperinsulinemia, and glucose intoler-
ance are related to a modifiable factor: weight gain in
adults, particularly in those persons in whom fat
accumulates around the waist, abdomen, and upper
body and within the abdominal cavity (this is also
called the android or central distribution pattern)
(Harris et al. 1987).

Physical Activity and NIDDM
Considerable evidence supports a relationship be-
tween physical inactivity and NIDDM (Kriska, Blair,
Pereira 1994; Zimmet 1992; King and Kriska 1992;
Kriska and Bennett 1992). Early suggestions of a
relationship emerged from the observation that soci-
eties that had discontinued their traditional lifestyles
(which presumably included large amounts of regu-
lar physical activity) experienced major increases in
the prevalence of NIDDM (West 1978). Additional
evidence for the importance of lifestyle was provided
by comparison studies demonstrating that groups of
people who migrated to a more technologically ad-
vanced environment had higher prevalences of
NIDDM than their ethnic counterpartswho remained
in their native land (Hara et al. 1983; Kawate et al.
1979; Ravussin et al. 1994) and that rural dwellers
had a lower prevalence of diabetes than their urban
counterparts (Cruz-Vidal et al. 1979; Zimmet 1981;
Taylor et al. 1983; King, Taylor, Zimmet, et al. 1984).
Many cross-sectional studies have found physi-
cal inactivity to be significantly associated with
NIDDM (Taylor et al. 1983; Taylor et al. 1984; King,
Taylor, Zimmet, et al. 1984; Dowse et al. 1991;
Ramaiya et al. 1991; Kriska, Gregg, et al. 1993; Chen
and Lowenstein 1986; Frish et al. 1986; Holbrook,
Barrett-Connor, Wingard 1989). Cross-sectional
studies that have examined the relationship between
physical activity and glucose intolerance in persons
without diabetes have generally found that after a
meal, glucose levels (Lindgarde and Saltin 1981;
Cederholm and Wibell 1985; Wang et al. 1989;
Schranz et al. 1991; Dowse et al. 1991; Kriska,
LaPorte, et al. 1993) and insulin values (Lindgarde
and Saltin 1981; Wang et al. 1989; McKeigue et al.
1992; Feskens, Loeber, Kromhout 1994; Regensteiner
et al. 1995) were significantly higher in less active
than in more active persons. However, some cross-
sectional studies did not find that physical inactivity
was consistently associated with NIDDM in either
the entire population or in all subgroups (King,
Taylor, Zimmet, et al. 1984; Dowse et al. 1991;
Kriska, Gregg, et al. 1993; Montoye et al. 1977;
Taylor et al. 1983; Fisch et al. 1987; Jarrett, Shipley,
Hunt 1986; Levitt et al. 1993; Harris 1991). For
example, the Second National Health and Nutrition
Examination Survey and the Hispanic Health and
Nutrition Examination Survey found that higher

125


Physical Activity and Health

levels of occupational physical activity among
Mexican Americans were associated with less NIDDM
(Harris 199 1). However, in contrast to findings from
the First National Health and Nutrition Examination
Survey (Chen and Lewenstein 1986), this associa-
tion was not found for either occupational or leisure-
time physical activity among blacks or whites.

Two case-control studies have found physical
inactivity to be significantly associated with NIDDM
(Kaye et al. 1991; Uusitupa et al. 1985). One was a
population-basednestedcase-controlstudy, inwhich
women aged 55-69 years who had high levels of
physical activity were found to be half as likely to
develop NIDDM as were same-aged women with low
levels of physical activity (age-adjusted OR = 0.5;
95% Cl, 0.4-0.7) (Kaye et al. 1991). Moderately
active women had an intermediate risk (OR = 0.7;
95% Cl, 0.5-0.9).

Prospective cohort studies of college alumni,
female registered nurses, and male-physicians have
demonstrated that physical activity protects against
the development of NIDDM (Table 4-8). A study of

male university alumni (Helmrich et al. 1991) dem-
onstrated that physical activity was inversely related
to the incidence of NIDDM, a relationship that was
particularly evident in men at high risk for develop-
ing diabetes (defined as those with a high BMI, a
history of high blood pressure, or a parental history
of diabetes). Each 500 kilocalories of additional
leisure-time physical activity per week was associ-
ated with a 6 percent decrease in risk (adjusted for
age, BMI, history of high blood pressure, and paren-
tal history of diabetes) of developing NIDDM. This
study showed a more pronounced benefit from vig-
orous sports than from stair climbing or walking. In
a study of female registered nurses aged 34-59 years,
women who reported engaging in vigorous physical
activity at least once a week had a 16 percent lower
adjusted relative risk of self-reported NIDDM during
the 8 years of follow-up than women who reported
no vigorous physical activity (Manson et al. 1991).
Similar findings were observed between physical
activity and incidence of NIDDM in a S-year pro-
spective study of male physicians 40-84 years of age

Table 4-8.  Cohort studies of association of physical activity with non-insulin-dependent diabetes mellitus
       (NIDDM)

Definition of              Definition of

study

Population

physical activity

NIDDM

Helmrich et al.
(1991)

Male college alumni

Leisure-time physical activity
(walking, stair climbing, and
sports)

Self-reported physician-
diagnosed diabetes

Manson et al.
(1991)

Female nurses

Single questions regarding number  Self-reported diagnosed
of times per week of vigorous     diabetes, confirmed by
activity              classic symptoms plus
                fasting plasma glucose
               L 140 mg/dl; two elevated
                plasma glucose levels on
                   two different occasions;
                 hypoglycemic medication
                               use

Manson et al.
(1992)

Male phystcrans

Single questions regarding number  Self-reported physician-
of times per week of vigorous     diagnosed diabetes
activity

126


The Effects of Physical Activity on Health and Disease

(Manson et al. 1992). Although the incidence of
diabetes was self-reported in these cohorts, concerns
about accuracy are somewhat mitigated by the fact
that these were studies of health professionals and
college-educated persons. In these three cohort stud-
ies, two found an inverse dose-response gradient of
physical activity and the development of NIDDM
(Helmrich et al. 1991; Manson et al. 1992).

In a feasibility study in Malmo, Sweden, physical
activity was included as part of an intervention
strategy to prevent diabetes among persons with
impaired glucose tolerance (Eriksson and Lindgarde
1991). At the end of 5 years of follow-up, twice as
many in the control group as in the intervention
group had developed diabetes. The lack of random
assignment of participants, however, limits the
generalizability,of this finding. A study conducted in
Daqing, China, also included physical activity as an
intervention to prevent diabetes among persons with
impaired glucose tolerance (Pan, Li, Hu 1995). After
6 years of follow-up, 8.3 cases per 100 person-years
occurred in the exercise intervention group and 15.7
cases per 100 person-years in the control group.

It has been recommended that an appropriate
exercise program may be added to diet or drug
therapy to improve blood glucose control and re-
duce certain cardiovascular risk factors among per-
sons with diabetes (American Diabetes Association
1990). Diet and exercise have been found to be most
effective for controlling NIDDM in persons who
have mild disease and are not taking medications
(Barnard, Jung, Inkeles 1994). However, excessive
physical activity can sometimes cause persons with
diabetes (particularly those who take insulin for
blood glucose control) to experience detrimental
effects, such as worsening of hyperglycemia and keto-
sis from poorly controlled diabetes, hypoglycemia
(insulin-reaction) either during vigorous physical
activity or-more commonly-several hours after
prolonged physical activity, complications from pro-
liferative retinopathy (e.g., detached retina), compli-
cations from superficial foot injuries, and a risk of
myocardial infarction and sudden death, particularly
among older people with NIDDM and advanced, but
silent, coronary atherosclerosis. These risks can be
minimized by a preexercise medical evaluation and
by taking proper precautions (Leon 1989, 1992). To

Main findings
0.94 (95% Cl, 0.90-0.98) or 6% decrease in
NIDDM for each 500 kcal increment

Dose
response*

Yes

Adjustment for confounder
and other comments
Adjusted for age, BMI, hypertension
history, parental history of diabetes

0.84 (95% Cl, 0.75-0.94) for 2 1 time
per week vs. < 1 time per week
vigorous activity

No

Adjusted for age, BMI, family history
of diabetes, smoking, alcohol consumption,
hypertension history, cholesterol history,
family of history coronary heart disease

0.71 (95% Cl, 0.54-0.94) for 2 1 .time per
week vs. < 1 time per week vigorous
activity

Yes

Adjusted for age, BMI, smoking, alcohol
consumption, reported blood pressure,
hypertension history, cholesterol history,
parental history of myocardial infarction

Abbreviations: BMI = body mass index (wt [kg]/ht [ml2 ); Cl = confidence interval.
*A dose-response relationship requires more than 2 levels of comparison. In this column, "NA" means that there were only 2 levels of
comparison; "No" means that there were more than 2 levels but no dose-response gradient was found; "Yes" means that there were
more than 2 levels and a dose-response gradient was found.

127


Physical Activity and Health

reduce risk of hypoglycemic episodes, persons with
diabetes who take insulin or oral hypoglycemic drugs
must closely monitor their blood glucose levels and
make appropriate adjustments in insulin or oral hy-
poglycemic drug dosage, food intake, and timing of
physical activity sessions.

Biologic Plausibility

Numerous reviews of the short- and long-term
effects of physical activity on carbohydrate metabo-
lism and glucose tolerance describe the physiologi-
cal basis for a relationship (Bjiirntorp and Krotkiewski
1985; Koivisto, Yki-Jarvinen, DeFronzo 1986;
Lampman and Schteingart 1991; Horton 1991;
Wallberg-Henriksson 1992; Leon 1992; Richter,
Ruderman, Schneider 1981; Harris et al. 1987).
During a single prolonged session of physical activ-
ity, contracting skeletal muscle appears to have a
synergistic effect with insulin in enhancing glucose
uptake into the cells. This effect appears to be related
to both increased blood Bow in the muscle and
enhanced glucose transport into the muscle cell.
This enhancement persists for 24 hours or more as
glycogen levels in the muscle are being replenished.
Such observations suggest that many of the effects of
regular physical activity are due to the overlapping
effects of individual physical activity sessions and
are thus independent of long-term adaptations to
exercise training or changes in body composition
(Harris et al. 1987).

In general, studies of exercise training have
suggested that physical activity helps prevent NIDDM
by increasing sensitivity to insulin (Saltin et al. 1979;
Lindgarde, Malmquist, Balke 1983; Krotkiewski
1983; Trovati et al. 1984; Schneider et al. 1984;
Ronnemaa et al. 1986). These studies suggest that
physical activity is more likely to improve abnormal
glucose tolerance when the abnormality is primarily
caused by insulin resistance than when it is caused
by deficient amounts of circulating insulin (Holloszy
et al. 1986). Thus, physical activity is likely to be
most beneficial in preventing the progression of
NIDDM during the earlier stages of the disease
process, before insulin therapy is required. Evidence
supporting this theory includes intervention pro-
grams that promote physical activity together with a
low-fat diet high in complex carbohydrates (Barnard,
Jung, Inkeles 1994) or programs that promote diet

alone (Nagulesparan et al. 1981). Thesestudies have
shown that diet and physical activity interventions
are much less beneficial for persons with NIDDM
who require insulin therapy than for those who do
not yet take any medication or those who take only
oral medications for blood glucose control.
  Cross-sectional studies also show that, com-
pared with their sedentary counterparts, endurance
athletes and exercise-trained animals have greater
insulin sensitivity, as evidenced by a lower plasma
insulin concentration at a similar plasma glucose
concentration, and increased `z*I-insulin binding to
white blood cells and adipocytes ,(Koivisto et al.
1979). Insulin sensitivity and rate of glucose dis-
posal are related to cardiorespiratory fitness even in
older persons (Hollenbeck et al. 1984). Resistance or
strength-training exercise has also been reported to
have beneficial effects on glucose-insulin dynamics
in some, but not all, studies involving persons who
do not have diabetes (Goldberg 1989; Kokkinos et
al. 1988). Much of the effect of physical activity
appears to be due to the metabolic adaptation of
skeletal muscle. However, exercise training may
contribute to improved glucose disposal and glucose-
insulin dynamics in both adipose tissue and the
working skeletal muscles (Leon 1989,1992; Gudat,
Berger, Lefebvre 1994; Horton 1991).
In addition, exercise training may reduce other
risk factors for atherosclerosis (e.g., blood lipid
abnormalities and elevated blood pressure levels), as
discussed previously in this chapter, and thereby
decrease the risk of macrovascular or atherosclerotic
complications of diabetes (Leon 1991a).
Lastly, physical activity may prevent or delay the
onset of NIDDM by reducing total body fat or specifi-
cally intra-abdominal fat, a known risk factor for
insulin resistance. As discussed later in this chapter,
physical activity is inversely associated with obesity
and intra-abdominal fat distribution, and recent
studies have demonstrated that physical training can
reduce these body fat stores (Bjdrntorp, Sjdstrom,
Sullivan 1979;BrownellandStunkard 1980; Despres
et al. 1988; Krotkiewski 1988).

Conclusions

The epidemiologic literature strongly supports a
protective effect of physical activity on the likeli-
hood of developing NIDDM in the populations

128


studied. Several plausible biologic mechanisms exist
to explain this effect. Physical activity may also
reduce the risk of developing NIDDM in groups of
people with impaired glucose tolerance, but this
topic needs further study.

Osteoarthritis

Osteoarthritis, the most common form of arthritis, is
characterized by both degeneration of cartilage and
new growth of bone around the joint. Because its
prevalence increases with age, osteoarthritis is the
leading cause of activity limitation among older
persons. The etiology of osteoarthritis is unknown,
and the risk factors and pathogenesis of osteoarthri-
tis differ for each joint group.

Whether an active lifestyle offers protection
against the development of osteoarthritis is not
known, but studies have examined the risk of devel-
oping it in relation to specific athletic pursuits.
Cross-sectional studies have associated competitive-
as opposed to recreational-running at high levels
and for long periods with the development of os-
teoarthritis seen on x-rays (Marti and Minder 1989;
Kujala, Kaprio, Sarna 1994; Kujala et al. 1995). On
the other hand, both cross-sectional and cohort
studies have suggested that persons who engage in
recreational running over long periods of time have
no more risk of developing osteoarthritis of the knee
or hip than sedentary persons (Lane 1995; Lane et al.
1986,1993; Panush et al. 1995; Panush et al. 1986;
Panush and Lane 1994). There is also currently no
evidence that persons with normal joints increase
their risk of osteoarthritis by walking.
Studies of competitive athletes suggest that
some sports-specifically soccer, football, and
weight lifting-are associated with developing os-
teoarthritis of the joints of the lower extremity
(Kujala, Kaprio, Sarna 1994; Kujala et al. 1995;
Rall, McElroy, Keats 1964; Vincelette, Laurin,
Levesque 1972; Lindberg, Roos, G&sell 1993).
Other competitive sports activities in which spe-
cific joints are used excessively have also been
associated with the development of osteoarthritis.
For example, baseball pitchers are reported to have
an increased prevalence of osteoarthritis in the
elbow and shoulder joint (Adams 1965; Bennett
1941). These studies are limited because they

involve small sample sizes. Further confounding
these studies is the high incidence of fractures,
ligamentous and cartilage injuries, and other inju-
ries to joints that occur with greater-than-average
frequency among competitive participants in these
sports. Because joint injury is a strong risk factor for
the development of osteoarthritis, it may not be the
physical activity but rather the associated injuries
that cause osteoarthritis in these competitive ath-
letes. In a study by Roos and colleagues (1994),
soccer players who had not suffered knee injuries
had no greater prevalence of osteoarthritis than did
sedentary controls. Regular noncompetitive physi-
cal activity of the amount and intensity recom-
mended for improving health thus does not appear
harmful to joints that have no existing injury.

Physical Activity in Persons with Arthritis
Given the high prevalence of osteoarthritis among
older people, it is important to determine whether
persons with arthritis can safely exercise and be
physically active. Experimental work with animals
shows that use of injured joints inhibits tissue repair
(Buckwalter 1995). More specifically, several stud-
ies have indicated that running accelerates joint
damage in animal models where osteoarthritis has
beenexperimentallyinduced (Armstronget al. 1993).
In contrast, several short-term studies of human
subjects *have indicated that regular moderate-
exercise programs, whether including aerobic or
resistance training, relieve symptoms and improve
function among people with both osteoarthritis and
rheumatoid arthritis (Ettinger and Afable 1994;
Allegrante et al. 1993; Fisher et al. 1991; Fisher et al.
1994; Fisher and Pendergast 1994; Puett and Griffin
1994). For example, it has been shown that after
regular physical activity, persons with arthritis have
a significant reduction in joint swelling (Minor et al.
1988). In other studies of persons with osteoarthri-
tis, increased levels of physical activity were associ-
ated with improved psychosocial status, functional
status, and physical fitness (Minor 1991; Minor and
Brown 1993). Furthermore, regular physical activ-
ity of moderate intensity has been found to raise the
pain threshold, improve energy level, and improve
self-efficacy among persons with osteoarthritis
(Minor et al. 1989; Chow et al. 1986; Holman,
Mazonson, Lorig 1989).

The Effects of Physical Activity on Health and Disease

129


Physical Activity and Health

Biologic Plausibility

The biologic effects of physical activity on the
health and function of joints have not been exten-
sively investigated, but some level of physical activ-
ity is necessary to preserve joint function. Because
hyaline cartilage has no blood vessels or nerves,
mature cartilage cells (chondrocytes) receive nour-
ishment only from the diffusion of substances
through the cartilage matrix from joint fluid. Physi-
cal activity enhances this process. In the laboratory,
putting pressure on cartilage deforms the tissue,
creating pressure gradients that cause fluid to flow
and alter osmotic pressures within the cartilage
matrix (Hall, Urban, Gehll991). The effect of such
loading on the metabolism of chondrocytes is not
well described, but when loading is performed
within the physiologic range, chondrocytes increase
proteoglycan synthesis (Grodzinsky 1993). In con-
trast, high-intensity loading and -repetitive high-
impact loads disrupt the cartilage matrix and inhibit
proteoglycan synthesis (Lammi 1993).
  The role of normal loading is confirmed by the
effect of inactivity on articular cartilage..lmmobility
leads to decreased cartilage proteoglycan synthesis,
increased water content, and decreased cartilage
stiffness and thickness. Disuse may make the carti-
lage more vulnerable to injury, and prolonged disuse
causes loss of normal joint function as the joint
cavity is obliterated by fibrous tissue.
  Studies of running on joint function in dogs with
normal joints have confirmed that running does
affect the proteoglycan and water content of cartilage
and does not lead to degeneration of articular sur-
faces or to degenerative joint disease (Arokoski et al.
1993). In contrast, in dogs with injured joints, run-
ning has been shown to cause arthritis (Buckwalter
1995).

Conclusions

Physical activity is essential for maintaining the
health of joints and appears to be beneficial for
control of symptoms among people with osteoar-
thritis. Although there is no evidence that physical
activity itself causes osteoarthritis, injuries sus-
tained during competitive sports have been shown
to increase the risk of developing osteoarthritis.

Osteoporosis

Osteoporosis is characterized by decreased bone
mass and structural deterioration of bone tissue,
leading to bone fragility and increased susceptibility
to fractures. Because bone mass and strength pro-
gressively decline with advancing age, this disease
primarily affects older persons (Cummings et al.
1985). Osteoporosis is more common among women
than among men, for at least three reasons: women
have lower peak bone mass than men, women lose
bone mass at an accelerated rate after menopause
when estrogen levels decline, and women have a
                             '
longer life span than men.

The most common potential fracture sites are
vertebrae of the chest and lower back, the distal
radius (or wrist), the hips, and the proximal hu-
merus (NIH 1984). Vertebral fractures can occur
spontaneously or with minimal trauma (e.g., bend-
ing forward or coughing); once deformed, the verte-
brae never return to their normal shape. These
fractures may be asymptomatic and discovered only
incidentally on a chest or spine x-ray. Accumulation
of such vertebral fractures causes a bent-over or
hunchbacked posture that is generally associated
with chronic back pain and often with gastrointesti-
nal and abdominal problems related to a lowering of
the rib cage.

In the United States, fractures of the hip account
for 250,000 of the 1.5 million fractures that are
attributed each year to osteoporosis. Hip fractures
are associated with more deaths (a 15-20 percent
l-year mortality rate), permanent disability, and
medical and institutional care costs than all other
osteoporotic fractures combined (Cummings et al.
1985; Rankin 1993). By age 90, about one-third of
women and about one-sixth of men will have sus-
tained a hip fracture.

In both men and women, the development of
osteoporosis may be related to three factors: a defi-
cient level of peak bone mass at physical maturity,
failure to maintain this peak bone mass during the
third and fourth decades of life, and the bone loss
that begins during the fourth or fifth decade of life.
Physical activity may positively affect all three of
these factors.

Physical activity may play a substantial role in
the development of bone mass during childhood and
adolescence and in the maintenance of skeletal mass

130


as a young adult. This inference is partly based on
findings that athletic young adults have a higher
density of bone mineral than sedentary young adults
(Kirchner, Lewis, O'Connor 1996; Grimston, Willows,
Hanley 1993; Conroy et al. 1993; Nichols et al. 1994;
Rubin et al. 1993), on reports that athletes have a
differential density of bones according to the sport
they train for (Robinson et al. 1995; Heinonen et al.
1995), and on evidence that increase in bone mass in
university students is related to higher levels of
physical activity (Reeker et al. 1992).
Beyond this hypothesized function in youth,
physical activity plays a well-established role
throughout the life span in maintaining the normal
structure and functional strength of bone. Pro-
longed bed rest or immobility causes rapid and
marked reduction in bone mineral density (Krolner
et al. 1983; Chesnut 1993; Donaldson et al. 1970).
Of particular public health interest is the degree to
which physical activity can prevent or slow the
bone loss that begins occurring in women as a
normal process after menopause. Cross-sectional
studies of postmenopausal women have shown that
bone mineral density is correlated with muscle
strength (Sinaki et al. 1986; Sinaki and Offord
1988), physical activity (Sinaki and Offord 1988;
Shimegi et al 1994; Jacobson et al. 1984; Talmage et
al. 1986), and cardiorespiratory fitness (Pocock et
al. 1986; Chow et al. 1986). Longitudinal studies of
postmenopausal women have attributed increases
in both cardiorespiratory fitness and bone mass to
physical activity (Chow et al. 1987; Dalsky et al.
1988). There is some evidence that through physi-
cal activity, osteoporotic women can minimize bone
loss or facilitate some gain in bone mineral content
(Krslner et al. 1983; Kohrt et al. 1995). However,
other studies have failed to show such benefits
(Nelson et al. 1991; Sandler et al. 1989; Cavanaugh
and Cann 1988). The intensity of the physical
activity and the degree to which it stresses the bones
may be crucial factors in determiningwhether bone
mass is maintained. Thus it is likely that resistance
exercise may have more pronounced effects than
endurance exercise, although this has not yet been
unequivocally established.

Several investigators have found that the posi-
tive effect of physical activity on the bones of both
premenopausal and postmenopausal women depends

The Effects of Physical Activity on Health and Disease

on the presence of estrogen. In postmenopausal
women, greater gain in bone density accrues when
physical activity and estrogen replacement therapy
occur simultaneously (Prince et al. 1991; Kohrt et al.
1995). In young, premenopausal women, however,
excessive amounts of vigorous training may lead to
a low estrogen level and secondary amenorrhea, with
subsequent decreased bone mass and increased risk
of stress fractures (Marcus et al. 1985; Drinkwater et
al. 1984; Allen 1994).

The exercise-associated changes in bone mineral
density observed over time among both premeno-
pausal and postmenopausal women are much less
pronounced than those differences observed cross-
sectionally between active and sedentary persons
(Drinkwater 1993). Cross-sectional studies demon-
strate differences of lo-15 percent in bone mineral
density at various sites (Aloia et al. 1988; Lane et al.
1986; Michel, Bloch, Fries 1989; Reeker et al. 1992),
whereas intervention studies show smaller gains of
l-5 percent (Krslner et al. 1983; Dalsky et al. 1988;
Nelson et al. 1991; Pruitt et al. 1992; Drinkwater
1993). These differences may be due to differences in
comparison groups, to follow-up duration insuffi-
cient to show large changes in bone mineral density,
or to measurement at different skeletal sites. Still to
be conducted are well-designed randomized clinical
trials that are of sufficient size and duration to
determine definitively the longitudinal effects of
physical activity change or the differential effects
of resistance and endurance activity on bone mineral
density.

Biologic Plausibility

Bone is a dynamic tissue that is constantly remod-
eling its structure by resorption and formation.
Physical activity, through its load-bearing effect on
the skeleton, is likely the single most important
influence on bone density and architecture (Lanyon
1996). Bone cells respond to mechanical loading by
improving the balance between bone formation and
bone resorption, which in turn builds greater bone
mass (Lanyon 1987,1993). The higher the load, the
greater the bone mass; conversely, when the skel-
eton is unloaded (as with inactivity), bone mass
declines. Glucose-6-phosphate, prostaglandins, and
nitric oxide play a role in mediating the mechanical

131


Physical Activity and Health

loading effect on bone (Pitsillides et al. 1995; Turner
et al. 1995; Tang et al. 1995). Because it is muscle
that exerts the largest forces on bone during physi-
cal activity, the role.of muscle mass and strength in
maintaining skeletal integrity should be explored
more fully.

Nonmechanical factors, such as age, hormonal
milieu, nutritional intake, and medications, are in-
creasingly being recognized as important determi-
nants of the bone's response to mechanical loading
(Lanyon 1996). The relative contributions of each of
these factors are currently under study and are not
yet clearly delineated.  Animal studies confirm a
difference in bone response to mechanical loading
with age and by estrogen status (Turner, Takano,
Owan 1995). The potential clinical relevance of this
research is to better define the optimal amount and
type of exercise for maintaining or increasing bone
mass, particularly with aging or in the absence of
estrogen replacement therapy after menopause.

Physical Activity and the

Prevention of Fractures and Falling
Studies of physical activity in relation to hip frac-
ture in women have generally found a lower risk of
hip fracture among those who were more active.
Three cohort studies have reported such a protec-
tive effect. One showed a statistically significant
protective effect among those reporting the most
recreational activity at baseline (Farmer et al. 1989),
one showed inverse but not statistically significant
associations for both work and leisure-time physi-
cal activity (Meyer, Tverdal, Falch 1993), and one
showed a significant protective effect of walking for
exercise (Cummings et al. 1995). Case-control stud-
ies have been more equivocal. One such study
found a significant protective effect for two levels of
past activity, but for recent activity only moderate
amounts of activity showed a significant protective
effect (Jaglal, Kreiger, Darlington 1993):Another
case-control study showed inconsistent effects
across a variety of physical activity classifications
(Cumming and Klineberg 1994).
  Nonskeletal factors that increase the risk of
fractures due to falls include limitations in activi-
ties of daily living (e.g., dressing and feeding one-
self); compromised gait, balance, reaction time,

and muscle strength; impaired vision; medication
use; and environmental hazards (Dunn et al. 1992;
Gilligan, Checovich, Smith 1993; Tinetti, Speechley,
Ginter 1988; Cummings et al. 1995). Various exer-
cises may help prevent falls by improving muscle
strength, functional capacity, gait, balance, and
reaction time. Tinetti and colleagues (1994) showed
a significant decrease in falls in the elderly concomi-
tant with an improvement in balance and gait achieved
through exercise. Province and colleagues (1995)
demonstrated a protective effect against falls through
general exercise and exercises designed to improve
balance. Moreover, Fiatarone and colleagues (1994)
have shown that even frail elderly persons who have
multiple chronic diseases benefit substantially from
resistance training. This well-controlled random-
ized trial demo