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

Abstract 

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±7.9yr; body mass index 29.6±4.6 and 29.1±5.4kg/m²; hip BMD 1.025±0.138 and 0.895±0.128g/cm²; KES 124.9±41 and 72.7±22.9N·m; L-LBM 10.3±1.5 and 7.0±1.2kg; 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.

Key Words: Allometric scaling, bone mineral density, muscle mass, physical activity level, quadriceps strength, rehabilitation