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Strength Training For Older Adults
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During the past few years there has been considerable interest in the aging process, and several studies have examined strategies for delaying various degenerative responses (Campbell et al 1994, Fiatarone et al 1990, Frontera et al 1988, Koffler et al 1992, Menkes et al 1993, Nelson et al 1994, Risch et al 1993, Tufts 1994, Westcott and Guy 1996).
Perhaps the most obvious and misunderstood aspect of the aging process is the undesirable change in body composition and physical appearance. It is estimated that approximately 80 percent of Americans are sedentary (Anderson et al 1997) and that 75 percent of adults are overweight (Scripps 1996), and there would appear to be a strong association between doing too little exercise and having too much bodyweight.
Generally, men and women add about 10 pounds of bodyweight every decade during the midlife years. The typical response is dieting, and according to a Tufts University study (1994) about 40 percent of American adults are presently following restricted-calorie diets. Unfortunately, dieting without exercise does not have a very high record of success. First, only 50 percent of those who begin dieting complete the program (McClernan 1992). Second, of those individuals who do lose weight, more than 90 percent regain it within one year (Brehm and Keller 1990). Third, about 25 percent of the weight lost during low-calorie diets is actually muscle tissue, which is already in short supply among most older adults (Ballor et al).
Research shows that men and women lose more than five pounds of lean body mass (mostly muscle) every decade of life due to disuse (Evans and Rosenberg 1992, Forbes 1976). So the 10-pound per decade increase in bodyweight actually represents a 20-pound problem with respect to body composition. That is, on a decade-by-decade basis, the aging adult has about five pounds less muscle and about 15 pounds more fat for a 20-pound change in physical appearance. This process is illustrated in Figure 1.
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Changes in bodyweight and body fat for two and three day per week training groups (N=1132).
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Because our muscles are the engines of our bodies, muscle loss has a profound impact on our physical ability and functional capacity. Losing muscle is similar to going from an eight-cylinder engine to a four-cylinder engine. As engine size is closely associated with fuel utilization, it is not hard to understand why less muscle leads to a lower metabolic rate. In fact, the progressive reduction in muscle tissue is largely responsible for a two-to-five percent-per-decade decrease in our resting metabolism (Evans and Rosenberg 1992, Keyes et al 1973).
When our resting metabolic rate slows down, calories that were previously used by muscle tissue are now routed into fat storage. In other words, the progressive weight gain known as creeping obesity is typically due to fewer calories being burned rather than more calories being consumed. That is why dieting does not solve the problem. In fact, dieting exacerbates the problem by further reducing muscle tissue and metabolic rate.
While adults should perform regular endurance exercise, such as walking and cycling, to enhance cardiovascular function, aerobic activities do little to prevent the gradual deterioration of the musculoskeletal system. In a study of elite middle-aged runners, the subjects lost about five pounds of muscle over a 10-year period in spite of extensive aerobic training (Pollack et al 1987).
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Copyright © 1998
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