IF EXERCISE DOES NOT INCREASE BONE MINERAL DENSITY, WHAT DOES IT CHANGE? / 体力科学

ABSTRACT

Exercise has been proposed as one strategy for improving or maintaining the structural competence of bone. In contrast with previous densitometric analysis using dual energy x-ray absorptiometry (DXA) which reported that areal bone mineral density (aBMD ; bone mineral content per projected area) increased with exercise, the studies using peripheral quantitative computed tomography (pQCT) revealed that an improvement in the mechanical properties of adult bone in response to exercise is related to negative changes in volumetric BMD (vBMD ; bone mineral content in a unit volume). Therefore, if exercise does not increase vBMD, what does it change? The pQCT studies showed that periosteal area and cortical area were significantly greater in trained bone, together with an increase in cortical thickness. Furthermore, by assessing geometric bone adaptation to mechanical loading, cortical thickness and the mechanical properties of trained and sedentary bone were compared along 64 directions centering the center of gravity of the bone on cross-sectional pQCT images. The differences in these parameters for both groups depended on the direction of measurement, suggesting that site-specific adaptation of bone to exercise is related to the geographical relation of bone to muscle. Thus, the improvement in the mechanical properties of bone in response to long-term physical exercise is related to geometric adaptation and not vBMD.