There is increasing 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.

Changes in bodyweight and body fat for two and three day per week training groups (N=1132).

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).

If losing muscle is the basic problem then adding muscle should be the logical solution. But is it possible for older adults to replace the muscle they have already forfeited? Absolutely. In fact, several studies have shown that both muscle mass can be increased at essentially any age through systematic strength training (Campbell et al 1994, Fiatarone et al 1994, Frontera et al 1988, Westcott and Guy 1996).

With respect to reversing body composition problems, strength exercise is effective for adding muscle, losing fat, raising resting metabolic rate, and increasing daily energy expenditure. Consider the results of a Tuft University study conducted by Campbell and his colleagues (1994). After 12 weeks of strength training (about 30 minutes per session, three days per week), 12 senior men and women added about three pounds of lean (muscle) weight, lost about four pounds of fat weight, raised their resting metabolism by almost seven percent, and increased their daily energy expenditure by 15 percent. That is, three months of relatively brief strength training sessions enabled these older adults to replace muscle, reduce fat and eat about 350 more calories per day in the process.

In a similar study conducted at the South Shore YMCA (Westcott 1995), 85 senior men and women performed about 30 minutes of strength exercise and 20 minutes of endurance exercise two days per week for a period of eight weeks. On average, the exercisers added two pounds of lean (muscle) weight, lost four pounds of fat weight, and increased their overall muscle strength by about 50 percent.

In addition to replacing muscle tissue, research reveals that men and women of all ages can increase their bone mineral density through regular strength training. Studies with senior men (Menkes et al 1993) and senior women (Nelson et al 1994) have shown significant gains in bone mineral density, indicating that strength exercise may reduce the risk of osteoporosis.

Another benefit of strength training is an enhanced glucose metabolism that may reduce the risk of adult onset diabetes. Research at the University of Maryland (Hurley 1994) showed a 23 percent improvement in glucose metabolism after four months of strength exercise.

Another study at the University of Maryland (Koffler 1992) demonstrated a 56 percent increase in gastrointestinal transit speed following three months of strength exercise. Because faster gastrointestinal transit speed may reduce the risk of colon cancer, this finding has important implications for older adults.

Researchers at the University of Florida (Risch et al 1993) have demonstrated that properly performed strength training can significantly reduce low back pain, and researchers at Tufts University (Tufts University 1994) have determined that strength exercise can alleviate arthritic discomfort.

Contrary to popular opinion, regular strength training results in lower resting blood pressure in seniors (Westcott et al 1996), as well as in mildly hypertensive individuals (Harris and Holly 1987). Strength exercise has also been shown to improve blood cholesterol profiles (Hurley et al 1988).

In addition to the physiological benefits associated with strength training, a recent Harvard University study (Singh 1997) showed significant psychological improvements as well. After 12 weeks of strength exercise 14 of 16 depressed seniors subjects no longer met the criteria for clinical depression.

Of course, for most men and women the major outcomes of strength training are simply looking better, feeling better, and functioning better on a day-to-day basis. Fortunately, seniors respond just as well to strength exercise as younger adults.

Senior Study Results
A large-scale study conducted at the South Shore YMCA (Westcott and Guy 1996) compared the results of young, middle, and older adults following an eight-week training program consisting of about 30 minutes of strength exercise and 20 minutes of endurance exercise.

The 1132 participants in this study included 238 young adults (21 to 40 years), 553 middle-aged adults (41 to 60 years), and 341 older adults (61 to 80 years). As shown in Table 1, all three age groups began the program with similar bodyweights (172.7 to 179.9 lbs.) and similar percent fat readings (25.6 to 27.2 percent). After eight weeks of exercise, the bodyweight and body composition changes were comparable for the three age groups. The 21 to 40 year-olds lowered their bodyweight by 2.6 pounds and their percent fat by 2.3 percent. The 41 to 60 year-olds decreased their bodyweight by 2.0 pounds and their percent fat by 2.1 percent. The 61 to 80 year-olds reduced their bodyweight by 1.7 pounds and their percent fat by 2.0 percent.

Changes in fat weight and lean (muscle) weight were also similar for the three age groups. The young adults lost 4.9 pounds of fat weight and added 2.3 pounds of lean weight. The middle-aged adults lost 4.4 pounds of fat weight and added 2.3 pounds of lean weight. The older adults lost 4.1 pounds of fat weight and added 2.4 pounds of lean weight.

Although all three age groups recorded significant reductions in resting blood pressure, the senior participants experienced the greatest improvement. Their diastolic blood pressure decreased 3.7 mm Hg, and their systolic blood pressure decreased 6.2 mm Hg. Perhaps most important, the older adult group began the exercise program with a systolic blood pressure above the hypertensive level (143 mm Hg), but ended within the normal systolic range (137 mm Hg).