The association between skeletal muscle mass and functional capacity outcomes in Chinese older adults: a national community-based study

BACKGROUND: Maintaining functional independence in older adults is a critical public health objective. Although skeletal muscle mass is recognized as a key contributor to functional capacity outcomes, the exact relationship between them among community-dwelling older adults requires further investigation. METHODS: This cross-sectional study analyzed data from 13,322 participants aged ≥65 years from the 2018 Chinese Longitudinal Healthy Longevity Survey (CLHLS). Appendicular skeletal muscle mass index (ASMI) was calculated using a validated anthropometric equation, while functional capacity outcomes were assessed using basic and instrumental activities of daily living (BADL/IADL) scores. Multivariable linear regression, generalized additive models, and threshold effect analysis were employed to evaluate associations, with adjustments for demographic, socioeconomic, lifestyle, and comorbidity factors. RESULTS: In fully adjusted models, ASMI showed significant inverse associations with both BADL score (β = -0.072, 95% CI: -0.103 to -0.042) and IADL score (β = -0.225, 95% CI: -0.290 to -0.159). Threshold effect analysis revealed sex-specific inflection points: below 6.2 kg/m² in men and 5.2 kg/m² below in women, ASMI was negatively associated with BADL/IADL scores, whereas above these thresholds, the associations weakened or reversed. Subgroup analyses indicated stronger effects among men, urban residents, and those with stroke or cardiovascular disease. CONCLUSION: Muscle mass demonstrates sex-specific, non-linear associations with functional capacity outcomes in older adults, identifying critical thresholds that may inform targeted strategies to preserve independence.