Effects of jump training on bone are preserved after detraining, regardless of estrogen secretion state in rats

Abstract

We investigated whether the effects of jump training on bone are preserved after a detraining period in female normal and estrogen-deficient rats. Forty-four 11-wk-old Wistar rats were divided into the following four groups: sham sedentary ( n = 12), sham exercised ( n = 11), ovariectomized sedentary ( n = 10), and ovariectomized exercised ( n = 11). An 8-wk exercise period was introduced in which the rats in the exercised groups were jumped 10 times/day, 5 days/wk. This was followed by 24 wk of detraining. At the end of the exercise period, the jump training significantly increased the bone mineral content of the tibia ( P < 0.001), measured by dual-energy X-ray absorptiometry. After the detraining period, the bone mineral content ( P < 0.01), strength ( P < 0.001), and cross-sectional widths ( P < 0.001) of the tibia in the exercised groups were still greater than in the sedentary groups, without significant surgery-exercise interactions, although bone stiffness in the fracture test ( P < 0.05) and bone area in the center-proximal region, as measured by dual-energy X-ray absorptiometry ( P < 0.05), showed significant surgery-exercise interactions. These findings suggest that the exercise effect on bone strength is preserved, accompanied by cross-sectional morphological changes, even under estrogen deficiency.