Cross-sectional study of weight-bearing activity on proximal femur bone mineral density

In this cross-sectional study we investigated the effect of compressive and tensile forces applied on the proximal femur during weight-bearing activit ies. Ninety-seven men (29.9 +/- 1.7 years) were divided into two groups: 69 exercisers who had practiced regular high-impact weight-bearing activities for at least 5 years and 28 controls who had been sedentary for at least 5 years. The maximum isometric hip abduction strength was measured. The bone mineral density (BMD) of the femoral neck and the greater trochanter was a ssessed using dual-energy X-ray absorptiometry (DXA). Controls were conside red as the reference population to calculate the Z score. Mean BMD values o f the femoral neck were 0.97 g/cm(2) on both sides in the exercisers and 0. 83 g/cm(2) on the right side and 0.84 g/cm(2) on the left side in the contr ols. Mean BMD values of the greater trochanter were 0.86 g/cm(2) on the rig ht side and 0.87 g/cm(2) on the left side in the exercisers, 0.73 g/cm(2) o n the right side and 0.72 g/cm(2) on the left side in the controls. The BMD was significantly higher in exercisers at both trochanteric and cervical s ites (P = 0.0001). Both left and right hip abduction strength was significa ntly greater in the exercisers than in the controls (P < 0.05) and was posi tively correlated to cervical and trochanteric BMD (P < 0.01), In the exerc iser group, the trochanteric Z score was higher than the cervical Z score a t both right (P = 0.06) and left (P = 0.002) sides. Therefore, the proximal femoral BMD was significantly greater in exercised subjects as compared wi th sedentary controls. The difference was observed at the level of both the femoral neck (where it is known anatomically that only compressive gravita tional forces are exerted) and the greater trochanter (where it is known th at tensile forces are exerted). This result suggests the participation of b oth compressive and tensile forces in the mechanisms by which exercise infl uences bone trophicity.