Effects of running training in immature and mature periods on bone formation in rats / 体力科学

ABSTRACT

The purpose of this study was to investigate the effects of running training on bone formation in rats in relation to the age training started. The first experimental period was set from 6 to 12 weeks (wks) old and the second from 12 to 19 wks old. Sixty-four Wistar strain 6-wk-old male rats were initially divided into a non-exercise (N) and an exercise (E) group. At 12 wks old, each group was subdivided into two groups, providing four groups non-exercise·non-exercise (NN), non-exercise·exercise (NE), exercise·non-exercise (EN) and exercise·exercise (EE) . Exercise consisted of treadmill running at a speed of 30 m/min, 60 mm day, 5 days wk. The animals were sacrificed before the experiment (6 wks old), post-first experiment (12wks old) and postexperiment (19 wks old), the bilateral tibiae were removed and their lengths, bone mineral content (BMC), bone mineral density (BMD) and bone histomorphometric parameters were measured. The tibial length was significantly shorter in 12-wk-old E than N rats and in 19-wk-old EE than NN. At 19 wks old, the total tibial BMD values were significantly higher in EE than NN, and the BMD values of the proximal and distal tibiae, where the cancellous bone was the main component, had increased markedly, whereas no differences between the diaphyseal BMD of each group were noted. Bone histomorphometry at 12 wks old, considered the immature period, showed that the osteoid surfaces and labeled surfaces tended to be increased by running training, but the bone volume was unchanged. In contrast, at 19 wks old, considered the early mature period, the osteoid surfaces showed a tendency to decrease and labeled surfaces to increase and consequently the bone volume increased albeit not significantly. These results suggest that 1) running training started in immature rats represses longitudinal tibial growth, 2) the cancellous bone is more sensitive then the cortical bone to this type of training and 3) training of early mature rats increases bone volume by increasing the efficiency of osteoid calcification.