RESEARCH to PRACTICE

Exercise: A Prescription to Delay the Effects of Aging

Loretta DiPietro, PhD, MPH; James Dziura, MPH

THE PHYSICIAN AND SPORTSMEDICINE - VOL 28 - NO. 10 - OCTOBER 2000

Aging is associated with marked alterations in body composition. Of greater importance than the prevention of obesity for health and function in older age is the maintenance of body weight, specifically, preservation of lean muscle mass. Past the seventh decade of life, a decline in body weight occurs, which is at least partially explained by a loss of muscle mass, a process known as sarcopenia. Evidence suggests that muscle mass decreases 3% to 6% per decade after age 60.

Not totally distinct from sarcopenia is the age-dependent increase in the proportion of total body fat, with preferential deposition in central and visceral areas, rather than as subcutaneous fat. As a result of such shifts in body composition, older individuals are at increased risk of several functional disorders. Thus, the preservation of skeletal muscle (both quantity and quality) plays an important role in adequate functional and metabolic resilience in older age.

Aging, Activity, and Muscles

Functional sequelae related to the loss of muscle tissue include insulin resistance, leading to type 2 diabetes mellitus, and impairments in muscle strength, maximal aerobic capacity, resting metabolic rate, immune response, and physical function and mobility. Although the loss of alpha-motor neurons with aging contributes to this muscle atrophy, increased sedentary behavior, catabolic illness, medications, and undernutrition also play important roles.

Inactivity. Bortz (1) was an early proponent of the hypothesis that disuse—or inactivity—causes many of the functional losses commonly attributed to aging, at every level from molecular to organ system. He noted that many of the physiologic changes attributed to aging per se are similar to those induced by enforced inactivity, such as during bed rest or during prolonged spaceflight. Indeed, hypogravity can serve as a useful model for studying the decline in functional reserve in aging, especially since physical inactivity increases as we age, and we depend more on automated processes in our society.

Bortz further proposed that the decline in physiologic function can be attenuated, or even reversed, by exercise (table 1). Ample epidemiologic and experimental data have demonstrated the positive relation between physical activity and physical function in aging (2,3). Perhaps of greater importance for older populations, however, is the relation between physical activity and the preservation of muscle mass, as sarcopenia has been linked to defects in carbohydrate metabolism as well as to frailty. Fiatarone-Singh (4) provides a comprehensive summary of the current data relating the benefits of aerobic, resistance, and lifestyle activity to body composition and indicators of physical and metabolic function in older people.

TABLE 1. Selected Health Benefits of Physical Activity Delays onset of or prevents some chronic diseases (eg, type 2 diabetes mellitus, coronary artery disease) Improves heart function Improves psychological well-being Lowers blood pressure Maintains everyday functional abilities (eg, walking up stairs, lifting objects) Preserves lean muscle mass Promotes weight maintenance

Mitigating the Effects of Aging

Unfortunately, there is a paucity of data relating exercise to weight maintenance and functional reserve in aging, especially in people older than 85. Future research should focus on the longitudinal study of muscle loss and functional resilience in older people and the extent to which this relationship can be modified by exercise. Further, study of interventions designed to improve the basic components of metabolic and physical function (eg, muscle size, strength, and fiber integrity) needs to demonstrate how these physiologic or metabolic improvements translate into better functioning in activities of daily living (5).

Public health recommendations. These now focus on regular, moderate physical activity, accumulated throughout the day, as sufficient for achieving a wide array of health benefits. The surgeon general's report (6) calls for incorporating at least 30 minutes of any physical activity into the daily schedule. When coupled with adequate calorie intake, regular participation in moderate-intensity activities (such as walking, gardening, housework, or yardwork) will promote weight maintenance and muscle strength, flexibility, coordination, and endurance. Therefore, such activity should be encouraged among older patients to preserve physical and metabolic function and independence.

Physician advice. Perhaps the first step in meeting these recommendations is a discussion about the benefits of exercise and an actual exercise prescription (written on a pad for patient reference) from the physician during a routine office visit. Each subsequent visit should include discussion about the patient's progress. Reminders to be active, along with safety tips, can also be sent periodically from the physician's office via postcards or newsletters.

Activity impediments. Finally, many other factors may affect physical activity behavior throughout life, and these factors become even more important in older age (see "Overcoming Barriers to Increased Physical Activity"). Many of these determinants, particularly some of the psychosocial and environmental factors, are especially amenable to change and should be the focus of regular physician-patient interactions, as well as community intervention efforts.

How to Increase Activity

Strategies for increasing physical activity among older patients include: (1) increased physician counseling and public education about the health effects of moderate physical activity, (2) increased senior and community center programs that are supervised and provide social support and other incentives for exercise, and (3) increased community availability and accessibility of safe physical activity and recreational facilities such as hiking, biking, and fitness trails; public swimming pools; and acres of park space.

References

1. Bortz WM II: Disuse and aging. JAMA 1982;248(10):1203-1208
2. DiPietro L: The epidemiology of physical activity and physical function in older people. Med Sci Sports Exerc 1996;28(5):596-600
3. Haskell WL, Phillips WT: Exercise training, fitness, health, and longevity, in Lamb DR, Grisolfi CV, Nadel E (eds): Perspectives in Exercise Science and Sports Medicine: Exercise in Older Adults, vol 8. Carmel, IN, Cooper Publishing Group, 1995, pp 11-52
4. Fiatarone-Singh MA: Body composition and weight control in older adults, in Lamb DR, Murray R (eds): Perspectives in Exercise Science and Sports Medicine: Exercise, Nutrition, and Weight Control, vol 11. Carmel, IN, Cooper Publishing Group, 1998, pp 243-293
5. King AC, Rejeski WJ, Cuchner DM: Physical activity interventions targeting older adults: a critical review and recommendations. Am J Prev Med 1998;15(4):316-333
6. US Department of Health and Human Services: Physical Activity and Health: A Report of the Surgeon General. Atlanta, DHHS, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, 1996, pp 29-37

Dr DiPietro is an associate professor in the department of epidemiology and public health and associate fellow in the John B. Pierce Laboratory at Yale University School of Medicine in New Haven, Connecticut. Mr Dziura is a predoctoral fellow in the department of epidemiology and public health at Yale University School of Medicine. Address correspondence to Loretta DiPietro, PhD, MPH, Dept of Epidemiology and Environmental Health, The John B. Pierce Laboratory, 290 Congress Ave, New Haven, CT 06519; e-mail to ldipietro@jbpierce.org.