The role of exercise in the prevention of osteoporosis.

The response of an individual's bone mass to exercise training will depend, in part, on their present level of functional activity and on the hormonal and nutritional milieus of bone tissue. For normally active, but not trained persons, an exercise training program may lead to a new bone mass as much as 5% to 10% above baseline. In an individual with a bone mass which is markedly reduced because of inactivity, poor nutrition, or hormonal deficiency (or excess, depending on the hormone), it is possible that exercise will result in even larger gains in bone mass. Training with weight-bearing exercises may serve as an osteogenic stimulus to both young and older individuals. If the training program is limited or restricted, however, older people may not show the same magnitude of change as do younger subjects. In women, low estrogen levels may reduce the apparent benefit from exercise training, as seen from the studies of amenorrheic athletes. Low bone mass may be related to an estrogen withdrawal effect as well as to the basic estrogen deficiency. Exercise training is likely to provide an osteogenic stimulus for the maintenance of bone mass when it is done in an environment of optimal hormonal levels and nutrition. Physical activity, however, may not be an effective substitute for estrogen therapy. Under optimal conditions, exercise training does provide an osteogenic stimulus to bone, resulting in an increase or maintenance of bone mass, when a loss might otherwise be expected. It is not realistic, however, to expect that exercise training will bring about a large increase in bone mass.(ABSTRACT TRUNCATED AT 250 WORDS)