Associations of upper- and lower-limb muscle health components—muscle mass, absolute strength, and muscle-specific strength—with gait speed in community-dwelling older adults

PURPOSE: Muscle health encompasses multiple components, including muscle mass, absolute strength, and muscle-specific strength (MSS). MSS, defined as strength relative to corresponding muscle mass, has emerged as a marker of muscle health, but its site-specific relevance to mobility remains unclear. Because these components are often examined separately, direct upper- and lower-limb comparisons are needed to clarify which indicators offer the most clinically relevant information on gait speed. We compared upper- and lower-limb muscle mass, absolute strength, and site-specific MSS in community-dwelling older adults. METHODS: This cross-sectional analysis included 284 community-dwelling adults aged ≥ 65 years. Handgrip strength, knee extension strength, arm and leg muscle mass, and usual gait speed were measured. Upper-limb MSS was calculated as handgrip strength/arm muscle mass, and lower-limb MSS as knee extension strength/leg muscle mass. Age-, sex-, and body mass index-adjusted linear regression models examined associations with gait speed and compared model fit. RESULTS: Mean age was 77.2 years; 77.1% were women. Arm and leg muscle mass were not associated with gait speed. Knee extension strength showed the strongest individual association (standardized β = 0.37, 95% confidence interval 0.23-0.51). Upper-limb MSS (β = 0.28, 0.15-0.40) and lower-limb MSS (β = 0.32, 0.21-0.44) were associated with gait speed. When entered simultaneously, upper-limb MSS (β = 0.18, 0.05-0.31) and lower-limb MSS (β = 0.27, 0.16-0.39) remained independently associated, and the combined MSS model showed the best fit. CONCLUSION: Site-specific MSS, particularly when assessed in both upper and lower limbs, may provide complementary mobility-related information beyond limb muscle mass alone.