EXERCISE

the training of the body to improve its function and enhance its fitness. The benefits of exercising are numerous. People who are physically fit are better able to carry out ordinary activities without fatigue or exhaustion and to resist disease, infection, and undue physical deterioration. Among adults, the health-related benefits of physical fitnessparticularly the fitness of the heart muscleare usually the major concern. Improved cardiovascular and respiratory function can be achieved through a program of aerobic (oxygen-requiring) exercises. In order to obtain these benefits, the exerciser must work his heart at training levels for at least 20 minutes three times a week. An individual's training level, measured in heartbeats per minute, can be reliably estimated by subtracting one's age from 220 and then multiplying the result by 65 percent. Thus the training heart rate for a 35-year-old is about 120 beats per minute. Walking, jogging, cycling, swimming, and exercise dancing are popular forms of aerobic training. In addition to aerobic conditioning, a balanced fitness program should include exercises that build muscular strength and those that increase flexibility (i.e., the range of movement around the joints). Weight training (q.v.) can achieve the first objective, as can the performance of push-ups, chin-ups, sit-ups, and other calisthenics that use the body's own weight as a resistance load. Stretching exercises serve to increase flexibility. Performance-related fitness (as opposed to health-related fitness) is important for individuals who require special skills in coordination, strength, and endurance. Athletes, for example, usually develop their muscles more fully. In most cases, the muscle tissues simply become harder and stronger as more fibres in the tissue are brought into use. Muscles do not increase in size unless they are deliberately forced to by repetitive contractions. Although there is no definitive evidence that exercise prolongs life, several epidemiological studies have shown that increased levels of physical activity are correlated with lowered risk of coronary heart disease, the major killer of adults in developed countries. Regular exercise has also been shown to be of benefit in controlling type II (adult-onset) diabetes and in lowering high blood pressure in at least some persons. The benefits of exercise do not, however, last more than a few months after the cessation of regular training. Even athletes who have attained a high level of conditioning will regress rapidly to a pre-training level once exercising stops. The desirable amount of activity for fitness varies from person to person according to the factors of age, build, health, and gender. Too much exercise can cause wear on the joints, leading to articular disease in later life, but this is a condition found most commonly in top-ranking athletes. The pitfall of most beginners is simply overexercising. Many people experience stiffness after the first few days of exercise, but this is harmless and transient. Those who are overweight, past middle age, or suffer from heart disease should consult a physician prior to starting any exercise program. the training of the body to improve its function and enhance its fitness. The terms exercise and physical activity are often used interchangeably, but this article will distinguish between them. Physical activity is an inclusive term that refers to any expenditure of energy brought about by bodily movement via the skeletal muscles; as such, it includes the complete spectrum of activity from very low resting levels to maximal exertion. Exercise is a component of physical activity. The distinguishing characteristic of exercise is that it is a structured activity specifically planned to develop and maintain physical fitness. Physical conditioning refers to the development of physical fitness through the adaptation of the body and its various systems to an exercise program. Additional reading Exercise as a key to health maintenance is found in Kenneth H. Cooper, The Aerobics Program for Total Well-being: Exercise, Diet, Emotional Balance (1982); Michael L. Pollock, Jack H. Wilmore, and Samuel M. Fox III, Exercise in Health and Disease: Evaluation and Prescription for Prevention and Rehabilitation (1984); Philip L. White and Therese Mondeika (eds.), Diet and Exercise: Synergism in Health Maintenance (1982); Bud Getchell and Wayne Anderson, Being Fit: A Personal Guide (1982); John E. Beaulieu, Stretching for All Sports (1980). Specific aspects of exercise for middle-aged or older people are the topic of Herbert A. Devries and Dianne Hales, Fitness After 50 (1982). Other special topics are treated in the Journal of the American Medical Association: Larry W. Gibbons et al., The Acute Cardiac Risk of Strenuous Exercise, J.A.M.A., 244(16):17991801 (Oct. 17, 1980); John J. Duncan et al., The Effects of Aerobic Exercise on Plasma Catecholamines and Blood Pressure in Patients with Mild Essential Hypertension, J.A.M.A., 254(18):260913 (Nov. 8, 1985); Ralph S. Paffenbarger et al., A Natural History of Athleticism and Cardiovascular Health, J.A.M.A., 252(4):491495 (July 27, 1984); and Steven N. Blair et al., Physical Fitness and Incidence of Hypertension in Healthy Normotensive Men and Women, J.A.M.A., 252(4):487490 (July 27, 1984). See also Kenneth H. Cooper, Running Without Fear: How to Reduce the Risk of Heart Attack and Sudden Death During Aerobic Exercise (1985); and Sidney Alexander, Running Healthy: A Guide to Cardiovascular Fitness (1980).What happens to the body during exercise and other intense physical activity is explained in many informative sources and texts. See Per-Olof Astrand and Kaare Rodahl, Textbook of Work Physiology: Physiological Bases of Exercise, 2nd ed. (1977); and George A. Brooks and Thomas D. Fahey, Exercise Physiology: Human Bioenergetics and Its Applications (1984). Public health aspects of physical activities and exercise are explored in a collection of articles in Public Health Reports, vol. 100, no. 2 (MarchApril 1985). Roy J. Shephard (ed.), Frontiers of Fitness (1971), discusses the physiology of exercise and desirable limits of fitness for people of different ages.The usefulness of recreational exercise was studied in Greek antiquity by Galen; see Robert Montraville Greene, A Translation of Galen's Hygiene (De sanitate tuenda) (1951). For a historical treatment of exercise and sport, see Richard D. Mandell, Sport, a Cultural History (1984), a scholarly study of physical activity as a component of culture; William J. Baker, Sports in the Western World (1982); and HISPA (International Association for the History of Physical Education and Sport), The History, the Evolution and Diffusion of Sports and Games in Different Cultures (1976). Kenneth H. Cooper Steven N. Blair