Lean body mass and leg power best predict bone mineral density in adolescent girls

Purpose: We evaluated anthropometric and performance measures that best pre dict bone mineral density (BMD) and bone mineral content (BMC) in 54 adoles cent girls (14.6 +/- 0.5 yr; 22.7 +/- 14.0 months past menarche). Methods: Whole body, femoral neck,greater trochanter, lumbar spine (L2-L4), and mid- femoral shaft BMD and BMC, and whole body bone-free lean mass and fat mass were assessed using DXA (Hologic QDR 1000/W). Knee extensor strength and le g power were assessed by isokinetic dynamometry and the Wingate Anaerobic P ower Test, respectively. Results: Whole body lean mass was correlated with BMD at all bone sites (r = 0.45-0.77; P < 0.001) and was more highly correl ated with bone at all sites than was body weight. Leg power was also associ ated with BMD at all sites (r = 0.41-0.67; P < 0.001), whereas leg strength correlated significantly with all sites (r = 0.41-0.53; P < 0.001) except the lumbar spine. Stepwise regression analyses revealed that 59% of the var iance in whole body BMD was predicted by lean mass alone. No other variable s, including Eat mass, height, months past menarche, leg power, or leg stre ngth, contributed additionally to the regression model. Similarly, lean mas s was the only predictor of lumbar spine and femoral shaft BMD (R-2 = 0.25, R-2 = 0.37, respectively), while femoral neck and trochanteric BMD were be st predicted by leg power (R-2 = 0.38, R-2 = 0.36, respectively). Similar b ut stronger models emerged using BMC as the outcome, with lean mass and leg power explaining the most variance in BMC values. Conclusion: In this grou p of adolescent girls, lean body mass and leg power best predicted BMC and BMD of the whole body, lumbar spine, femoral shaft, and hip, which may sugg est an important role for muscle mass development during growth to maximize peak bone density.