二足起立ラット大腿骨の運動適応 : 骨密度と横断面形状からみた分析

抄録

Effects of erect bipedal standing exercise on the hind-leg bone density and cross-sectional geometric properties were simultaneously investigated in seventeen growing male rats, divided into a control group and an exercise group. Using a bipedal training box, in which rats achieved a fully upright stance through positively reinforced operant conditioning, the exercise group was burdened with bipedal standing exercise from 64 days to 140 days of age, totalling 136 to 138 sessions. At the age of 140 days, the left femur was dissected out, and ten serial cross sections of the femoral diaphysis were cut from proximal to distal. In the present experiment, bone density and cross-sectional geometric properties were measured at a 46% level in a sectioned block of 45 to 50% level, using pQCT (peripheral quantitative computed tomography). The bipedal standing exercise had the following effects on the femoral diaphysis: (1) Bone density per unit volume tended to increase, though without statistical significance; (2) total bone area of the cross section of the femur shaft, cortical area of the cross section, cortical thickness (mean value), and minimum principal moment of inertia increased with statistical significance. These results suggest that adaptation of mechanical strength of a rat femur to bipedal standing exercise depends mainly on the changes in the cross-sectional geometric properties of the bone, rather than on an increase in bone density.