Sport Science In Successful Aging

Soon Ahn, M.D., Physical Medicine
and Rehabilitation, Jacksonville, FL

Advancing age is associated with changes in body composition. Loss in muscle mass causes the age-associated decreases in basal metabolic rate, muscle strength, and activity levels, which in turn cause the decreased energy requirements of the elderly. In sedentary individuals, the main determinant of energy expenditure is fat free mass, which declines by about 15% between the third and eighth decades of life. Increased body fat, along with increased abdominal obesity, are thought to be directly linked to the greatly increased incidence of Type II diabetes among the elderly. Sarcopenia (loss in muscle mass) is a direct cause of the age-related decrease in muscle strength. Reduced muscle strength in the elderly is a major cause of their increased disability. The high prevalence of falls among the institutionalized elderly may be a consequence of their lower muscle strength.

To what extent are these changes inevitable consequence of aging? Data examining young and middle-aged endurance trained men demonstrate that body fat stores and maximal aerobic capacity were not related to age but rather to the total number of hours of exercise per week.

Klitgaard and colleagues ³ found that older endurance athletes (runners and swimmers) display fat free mass and muscle strength similar to those seen in sedentary aged-matched controls, an indication that endurance exercises alone may not prevent sarcopenia.

Ballor and colleagues ⁴ compared the effects of resistance training to those of diet restrictions alone in obese women. They found that resistance exercise training results in increased strength and gains in muscle size as well as preservation of fat free mass during weight loss.

The two-hour plasma glucose level during an oral glucose tolerance test increases by an average of 5.3 mg/dl per decade, and fasting plasma glucose increases by an average of 1mg/dl per decade. ⁵

Per study by Shimokata and co-workers ⁶, by assessing level of obesity, patterns of body fat distribution, activity and fitness levels, they examined the independent effect of age on glucose tolerance. They found no significant differences between the young and middle-aged groups; however, the old groups had higher glucose and insulin values than young or middle-aged groups. The major finding of this study is that the decline in glucose tolerance from the early-adult to the middle-age years is explained by secondary influences (fatness and fitness) whereas the decline from mid-life to old age still is also influenced by chronologic age. This age associated change in glucose tolerance can result in NIDDM. Hughes and co-workers ⁷ demonstrated that regularly performed aerobic exercise without weight loss resulted in improved glucose tolerance, rate of insulin stimulated glucose disposal and increased skeletal muscle glucose transport protein levels in older glucose intolerant subjects. Aerobic exercises combined with weight loss has been demonstrated to increase insulin action to a greater extent than weight loss through diet restriction alone. Aerobic exercise has been an important recommendation for the prevention and treatment of many of the chronic diseases associated with old age such as NIDDM, hypertension, heart disease and osteoporosis.

Age-related decreases in functional status:

What are the possible contributory factors to musculoskeletal injury in the older athlete?

• Decreasing flexibility with aging - primary cause is disuse.
• Decreased nerve conduction and reaction time-15% decrease between age 30-70.
• Decreased hearing and/or vision associated with unsteady gait-use of a stationary bicycle may be useful for those with balance problems.
• Degenerative joint disease.
• Rheumatoid arthritis-increased incidence with aging: women > men.
• Gout-increased incidence over age 60: men > women, should curtail activity during acute attack, utilizing adequate rest periods, appropriate splinting and medications.
• Decreased muscle mass-results in decreased strength and shock absorption.
• Osteoporosis-more significant for females, may predispose older individuals to increased fractures. Regular weight bearing exercise may play a role in prevention.

What are the guidelines for achieving cardiorespiratory and muscular fitness and how do they relate to the mature athlete?

The American College of Sports Medicine (ACSM) guidelines for developing and maintaining cardiorespiratory and muscular fitness recommend exercise at intensity levels of ¹ 50-85% VO2max; ² 60-90% HRmax: or ³ 40-85 METS (maximum MET level). Three to five sessions per week (frequency), for 20-60 minutes (duration) completes the prescription. Resistance training recommendations include one set (8-12 repetitions) of 8-10 exercises that condition major muscle groups at least two times each week. The mature athlete may have pre-existing medical conditions (e.g. arthritis, coronary artery disease, COPD) or certain age-related changes that limit the ability to achieve the ACSM's guidelines. Starting an older athlete at levels far below those outlined may be indicated. Exercising at lower levels may provide some modest aerobic benefit.

What are some of the specific benefits of regular exercise in the mature athlete?

Among some of the specific adaptations to exercise, one may see improvements in cardiac output, a decline in resting heart rate, improved cholesterol, a decline in blood pressure, and increased cardiovascular fitness. Improvements in minute ventilation and vital capacity but not chest wall compliance also are observed. Bone density, muscle strength, flexibility, and coordination also are improved. Perhaps just as important are improvements in mood and self-esteem with opportunities for contact with peers. An organized program of regular physical activity may enhance their socialization and decrease their idle time.

Conclusion

There is no other group that can benefit more from regularly performed exercise than the elderly. While balance, aerobic and strength conditioning are highly recommended, only strength training can stop or reverse sarcopenia. Increased muscle strength and mass in the elderly can be the first step for maintaining independence.

References

1. Garrett W.E., Kirkendall DT. Exercise and Sport Science 2000
2. Mellion M.B., Sports Medicine Secrets 2^nd Edition.
3. Klitgaard H, Zhou M, Schiaffino S, Betto R, Salviati G, Saltin B, Aging alters the myosin heavy chain composition of single fibers from human skeletal muscle. Acta Physio Scand 1990; 140:55-62.
4. Ballor DL, Katch VL, Becque MD, Marks CR, Resistance weight training during caloric restriction enhances lean body weight maintenance. Am J Clin Nutr 1988;47:19-25.
5. Davidson MB, The effect of aging on carbohydrate metabolism. A review of the English literature and a practical approach to the diagnosis of diabetes mellitus in the elderly. Metabolism 1979; 28:688-705.
6. Shimokata H, Muller DC, Fleg JL, Sorkin J, Ziemba AW, Andes R. Age as independent determinant of glucose tolerance. Diabetes 1991;40:44-51.
7. Hughes VA, Fiatarone MA, Fielding RA, et al. Exercise increases muscle GLUT 4 levels and insulin action in subjects with impaired glucose tolerance. Am J Physiol 1993;264:E855-E862.

Jacksonville Medicine / August/September, 2001

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