MAXIMUM LEG POWER BEST PREDICTS FEMORAL NECK AND LUMBAR SPINE BMD IN 14-YEAR OLD GIRLS 878

Abstract

Research has demonstrated that body weight best predicts bone mineral density and content in adolescents. Little is known about the associations between bone mass of the appendicular and axial skeleton and measures of body composition, muscle strength and muscular power and in adolescent girls. This cross-sectional study examined these relationships in 39 high school girls(age=14.6±0.5 y; 61.2±14.3 kg; 164.4±5.9 cm; 24.7±6.7% fat) who averaged 1.8±1.2 years past menarche. Bone mineral content (BMC) and bone mineral density (BMD) were assessed at the whole body, lumbar spine, femoral neck, and femoral mid-shaft by dual energy x-ray absorptiometry (Hologic QDR-1000/W). Strength of the left knee extensors was measured by isokinetic dynamometry (Kin-Com 500H) and maximum leg power was assessed using the Wingate Anaerobic Power Test with the workload set at 7.5% of body weight. Stepwise multiple regression, which included whole body lean mass, whole body fat mass, maximum knee extensor force, maximum leg power, and years past menarche revealed that lean mass and fat mass independently predicted whole body BMC (R2=0.87, p<0.0001), but that lean mass was the strongest predictor (β=0.73 vs. 0.29). At the femoral midshaft, whole body lean mass was the only independent predictor of BMD(R2=0.36, p<0.0001). Using the same regression model, maximum power was the single independent predictor of femoral neck BMD (R2=0.39, p<0.0001) and lumbar spine BMD (R2=0.13, p<0.026). In conclusion, results from this preliminary study indicate that whole body lean mass best predicts bone mass of the appendicular skeleton in 14-year old girls, whereas bone of the axial skeleton in this population is best predicted by maximum leg power. Further, these results suggest that the most important component of weight and its relationship to bone is lean, not fat mass.