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