Doctors at Tufts University have shown that even modest exercise with weights can boost the immune system and reverse sarcopenia — muscle loss that can lead to bone weakening. A group of 90-year-olds improved their strength a whopping 174 percent after just eight weeks of weightlifting in one study.

Much of the disability, loss of function, and ensuing loss of independence in seniors results from diminished muscle strength as well as low aerobic fitness. In the average person, muscle strength peaks between the ages of 20 and 30 then slowly decreases.

Without strength training, most people show a 30 percent loss in overall strength by age 70. The prime reason is a reduction in lean muscle mass — sarcopenia — which may be the result of inactivity, aging, or a combination of both.

Besides reducing the effects of sarcopenia, weightlifting and exercise can reduce the incidence of falls. By some estimates, 40 percent of persons over age 65 fall at least once a year, and persons 85 years and older may be more likely to die from falls and hip fractures than from heart disease.

A study in the December 28, 2004, issue of Neurology showed yet another benefit of longer and more intense physical activity for seniors: maintained cognitive skills. The European study showed that over 10 years, the cognitive decline in men who had reduced their daily physical activity by an hour or more was 2.6 times greater than the decline in men who had maintained their activity.