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

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ObjectivesThe 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 designCross-sectional analysis at a university research laboratory. Main outcome measures: Community-dwelling older women (n=96, 73.9±5.6 years, BMI=26.5±4.7kg/m2) 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. ResultsMuscle 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 β=0.47, p<0.01) and relative adiposity (β=-0.33, p<0.01) were the strongest independent predictors of composite LEPF Z-score explaining 24% and 17% of the variance, respectively. ConclusionsMuscle 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.