Study Objective:​To assess the effect of weight-bearing exercise training and subsequent detraining on lumbar bone mineral content in postmenopausal women.

Design:​Non-randomized, controlled, short-term (9 months) trial and long-term (22 months) exercise training and detraining (13 months).

Setting:​Section of applied physiology at a university school of medicine.

Patients:​Thirty-five healthy, sedentary postmenopausal women, 55 to 70 years old. All women completed the study. There was 90% compliance with exercise training.

Interventions:​All women were given calcium, 1500 mg daily. The exercise group did weight-bearing exercise (walking, jogging, stair climbing) at 70% to 90% of maximal oxygen uptake capacity for 50 to 60 min, 3 times weekly.

Measurements and Main Results:​Bone mineral content increased 5. 2% (95% confidence interval [CI], 2.0% to 8.4%;​P= 0.0037) above baseline after short-term training whereas there was no change (-1.4%) in the control group. After 22 months of exercise, bone mineral content was 6.1% (95% CI, 3.9% to 8.3% above baseline;​P=0.0001) in the long-term training group. After 13 months of decreased activity, bone mass was 1.1% above baseline in the detraining group.

Conclusions:​Weight-bearing exercise led to significant increases above baseline in bone mineral content which were maintained with continued training in older, postmenopausal women. With reduced weight-bearing exercise, bone mass reverted to baseline levels. Further studies are needed to determine the threshold exercise prescription that will produce significant increases in bone mass.