EFFECTS OF IMPACT-LOADING ON BONE MASS AND STRENGTH IN OVARIECTOMIZED RATS

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The first study was designed to investigate the effect of high-impact and low-repetition jump exercise on bones in ovariectomized rats. Forty female Wistar rats were sham-operated (Sham) or ovariectomized (OVX) at the age of 11 weeks. The rats were randomly divided into the following 4 groups ; Sham-Sedentary (SS, n=10), Sham-Exercised (SE, n=10), OVX-Sedentary (OS, n=10), and OVX-Exercised (OE, n=10). The rats started the jump-training at the age of 12 weeks. The jump-training protocol was 10 times/day, 5 days/week and the jumping height was 40 cm. After 8 weeks of training, the mass and breaking force in the tibia and ulna, cross-sectional areas of diaphysis in the tibia and serum bone turnover markers were measured. The jump-training significantly increased the fat-free dry weight, ash weight and ultimate breaking force in the tibia. The rate of increase in these parameters was similar in both the Sham and OVX groups. On the other hand, in the ulna, there were no significant changes in the ultimate breaking force. The jump-training significantly increased the periosteal perimeter and cortical area, though the increase in these parameters in OE compared to OS was lower than that in SE compared to SS.The jump-training significantly increased serum osteocalcin in the OVX groups, as well as in the Sham groups.The second study was focused on exercise frequency in one week to increase bone mass and strength in ovariectomized rats. The experimental protocol was like as the first study. Jump exercise with only one times/week increased bone mass and strength in ovariectomized rats, though did not increase cross-sectional cortical area of diaphysis. These results suggest that high-impact and low-repetition training had beneficial effects on bone formation and bone biomechanical properties in OVX rats, as well as in Sham rats.