This study includes completion of a large, partially randomized clinical trial evaluating the effect of a 1-year exercise intervention on total body and regional BMD in two populations (hormone replacement therapy [HRT] versus no HRT) of postmenopausal women with a previous history of physical inactivity. A major hypothesis is that, compared to the no-exercise group, the exercise intervention will be an effective alternative to reduce the risk of osteoporosis and the exercise effects will be larger in the cohort of women on HRT than those not on HRT.