Beyond Adiposity: Lean Mass and Bone Mineral Content as Markers of Muscle Weakness and Physical Performance in Older...

Background and Objectives: The contribution of body composition to muscle weakness and physical performance in older adults remains incompletely defined. This study aimed to evaluate the discriminative capacity of total and segmental body composition variables to identify muscle weakness and low physical performance in older adults. Materials and Methods: A cross-sectional study was conducted in 268 community-dwelling older adults (72.2 ± 8.2 years; 81.3% women). Body composition (lean mass, fat mass, and bone mineral content [BMC], total and segmental) was assessed using dual-energy X-ray absorptiometry. Muscle weakness was assessed by handgrip strength (≤27 kg in men; ≤16 kg in women), and low physical performance by the Short Physical Performance Battery ≤8. Sex-stratified receiver operating characteristic (ROC) analyses were performed. Results: No significant differences were found between sexes for age (p = 0.307) or body mass index (p = 0.892). However, men exhibited significantly higher waist circumference (105.2 ± 11.9 vs. 97.8 ± 12.4 cm; p < 0.001) and handgrip strength (30.3 ± 6.8 vs. 18.3 ± 4.6 kg; p < 0.001) than women. Regarding body composition, men presented higher total lean mass (50.4 ± 6.9 vs. 37.2 ± 4.6 kg; p < 0.001) and total bone mineral content (2666 ± 483 vs. 1940 ± 286 g; p < 0.001). Conclusions: Body composition variables showed higher discriminative capacity for muscle weakness than for low physical performance. The ability of lean mass and BMC to identify low physical performance was modest in both sexes, suggesting that structural body composition variables alone may be insufficient to discriminate complex functional impairment in older adults.