Associations Between Physical Activity, Muscle Mass, and Functional Outcomes in Community-Dwelling Older Adults from Chile: A Cross-Sectional Study

Population aging increases the need to preserve functional independence in older adults. This cross-sectional study examined the associations between physical activity (PA), percentage muscle mass (%Muscle), and functional outcomes in 129 community-dwelling older adults (mean age 72.05 ± 8.46 years). PA was assessed with the IPAQ (MET-min/week), body composition via bioelectrical impedance, and outcomes included the Timed Up and Go test (TUG), handgrip strength, calcaneal bone status (QUS-derived T-score), and SF-36 Physical Component Summary (PCS). Total PA showed a small positive association with handgrip strength (r = 0.19, p = 0.031). Bootstrapped mediation analyses (5000 resamples), adjusted for age and BMI, revealed no statistically significant indirect effects through %Muscle (all 95% CIs included zero). Exploratory simulations based on observed associations suggested modest changes in handgrip strength with hypothetical increases in PA (+0.25 kg at +20% METs; +0.62 kg at +50% METs), while changes in other outcomes were minimal. These findings indicate that, in this relatively well-functioning sample, total PA volume has limited explanatory value for variability in functional and musculoskeletal outcomes. Muscle mass did not statistically account for the PA–function relationship. Given the cross-sectional design, causal inferences cannot be drawn. These findings suggest that targeted exercise programs emphasizing muscle strength and neuromuscular function may be more effective than increases in overall physical activity volume for preserving functional capacity in older adults.