BONE RESPONSES TO INCREASED MECHANICAL LOADING BY INCREASING ITS SIZE, TRABECULAR DENSITY OR BOTH OF THEM

Abstract

256 It is well possible that training could increase bone strength through site-specific changes in bone composition, size and structure without a notable increase in volumetric density. This study focused on this issue by comparing 14 Finnish female weightlifters with 14 young female students. Trabecular and cortical density (g/cm3), cross-sectional area (mm2) and strength indices (BSI, mm3) of the distal radius, radius midshaft, distal femur and tibial midshaft were determined by pQCT. ANCOVA was used for estimating the differences, the weight being the covariate. Cortical density was similar in both groups. However, trabecular density showed site-specific differences in favor of the weightlifters, the benefits being 11% (p=0.074) at the distal radius and 16% (p<0.001) at distal femur. The cortical area of the bones of the weightlifters was 35% (p=0.003) larger at distal radius, 10% (p=0.009) at radial shaft, and 10% (p=0.11) at tibial midshaft. Consequently, the lifters' BSI values were higher too, the difference being 32% (p=0.026) at distal radius. These results show that the observed differences in the distal radius between the groups are mainly due to enlarged radius (especially enlarged bone cortex) rather than higher bone density. On the other hand, weightlifters' trabecular tissue at the distal femur is denser but the bone is not bigger (5%, p=0.954). We suggest that bones mostly experiencing bending-type loading are larger than their normal counterparts while the sites mostly experiencing compressive-type loading have denser trabecular structure.