Muscle quality and relative adiposity are the strongest predictors of lower-extremity physical function in older women

Objectives: The aim of this study was to examine the relative contributions of physical activity, adiposity, lean mass and muscle quality to lower-extremity physical function (LEPF) in older women. Study design: Cross-sectional analysis at a university research laboratory. Main outcome measures: : Community-dwelling older women (n = 96, 73.9 +/- 5.6 years, BMI = 26.5 +/- 4.7 kg/m(2)) were assessed for body composition via dual-energy X-ray absorptiometry, leg extension power using the Nottingham power rig, muscle quality (W/kg) as the ratio of leg extension power (W) to lower-body mineral free lean mass (kg) and moderate-intensity physical activity via questionnaire. A composite measure of LEPF was calculated by summing Z-scores of the 6-min walk, 8-foot up-and-go and 30-s chair stand tests. Results: Muscle quality and physical activity were associated with all measures of LEPF (all p < 0.01). Relative adiposity was related to the 6-min walk and 30-s chair stand (both p < 0.01); lower-body mineral-free lean mass was not related to any measure of LEPF (p > 0.05). Hierarchical linear regression analyses revealed that muscle quality (standardized beta = 0.47, p < 0.01) and relative adiposity ( beta = -0.33, p < 0.01) were the strongest independent predictors of composite LEPF Z-score explaining 24% and 17% of the variance, respectively. Conclusions: Muscle quality and relative adiposity are the strongest independent predictors of LEPF in older women. These findings suggest that maintaining muscle quality, especially relative to adiposity, may be a critical target for interventions to prevent declines in physical function in older women. (C) 2014 Elsevier Ireland Ltd. All rights reserved.