Muscle strength can better differentiate between gradations of functional performance than muscle quality in healthy 50–70 y women

OBJECTIVE: It is not known which laboratory indices of muscle mass, strength or quality can distinguish functional performance in healthy middle aged women. The aim of this study was to (a) examine the association between upper leg lean tissue mass, knee extensor strength, muscle quality (strength per unit lean tissue mass) and functional performance and (b) to determine the utility of tertiles of muscle strength and muscle quality to distinguish gradations of functional capacity in healthy 50–70 y women. METHODS: Using a cross-sectional study design, one hundred and twenty-eight healthy 50–70 y women (mean age: 60.4, SD = 5.1 y) underwent body composition assessment (dual X-ray absorptiometry) and performed maximal voluntary isometric contractions of the knee extensors (Con-Trex Dynamometer). Functional performance was assessed using a 5 repetition and 30 s chair rise test and 900 m gait speed test. RESULTS: Ordered by muscle strength or muscle quality, those in the highest tertile (T1) demonstrated greater functional performance than those in lowest tertile (T3). There was no association between upper leg lean tissue mass and functional performance (r = ≤0.06). Muscle strength explained a greater proportion of the variance in all functional performance measures relative to muscle quality (R(2) = 0.13–0.36 vs. R(2) = 0.11–0.16). CONCLUSION: Upper leg lean tissue mass is not associated with physical performance in healthy 50–70 y women. These results suggest strength relative to the body mass being accelerated distinguishes gradations in functional performance better than muscle quality healthy 50–70 y women.