Prevention of involutional bone loss by exercise.

To ascertain whether exercise could prevent involutional bone loss, we studied 18 postmenopausal women, half of whom exercised for 1 h three times a week. Total and regional bone mass were measured before and after 1 year of exercise by the techniques of total-body neutron activation analysis (total body calcium) and photon absorptiometry (bone mineral content) of the distal radius. Total body potassium was measured by whole body counting. Bone mineral content and total body potassium did not change significantly in either group. Total body calcium increased in the exercise group from 781 +/- 95 g of 801 +/- 118 g (SD). In contrast, total body calcium decreased in each subject in the sedentary group. The daily calcium balance derived from the difference in total body calcium measurements was significantly different in the two groups of women (P less than 0.001). These data support the hypothesis that exercise can modify involutional bone loss.