Muscle Mass Is More Strongly Related to Hip Bone Mineral Density Than Is Quadriceps Strength or Lower Activity Level in Adults Over Age 50 Year

This cross-sectional study examined whether reduced hip bone mineral density (BMD) is better explained by isokinetic knee extensor strength (KES), lower limb lean body mass (L-LBM), or Physical Activity Scale for the Elderly (PASE). Through population-based recruitment, 1543 adults without knee osteoarthritis were recruited. For men and women respectively, means ± SD were age 60.8 ± 8.0 and 61.1 ± 7.9 yr; body mass index 29.6 ± 4.6 and 29.1 ± 5.4 kg/m²; hip BMD 1.025 ± 0.138 and 0.895 ± 0.128 g/cm²; KES 124.9 ± 41 and 72.7 ± 22.9 N·m; L-LBM 10.3 ± 1.5 and 7.0 ± 1.2 kg; and PASE 206.4 ± 99.7 and 163.8 ± 77.0. The relationship between BMD and KES in men (r² = 0.21, p ≥ 0.002) and women (r = 0.23, p < 0.001) was significant before adjustment. However, this association was no longer significant after controlling for L-LBM. Even after controlling for age, race, and sex, the association between BMD and KES was better explained by L-LBM (partial R² = 0.14, p < 0.001) than by PASE (partial R² = 0.00). Allometric scaling of KES to body size attenuated the association of BMD with KES (Std Beta = 0.03). The significant association between BMD and L-LBM (Std Beta = 0.36) remained stronger than that between BMD and weight (Std Beta = 0.21). Therefore, muscle mass accounted for a greater proportion of the variance in hip BMD than KES or activity level and explained a significant proportion of the association between weight and BMD.