The skeletal muscle function deficit: From an operational definition to clinic results from the InCHIANTI longitudinal study

Age-related muscle dysfunction is a major contributor to disability, frailty, and poor clinical outcomes in older adults. Skeletal Muscle Function Deficit (SMFD) framework integrates multiple domains as: muscle mass, muscle density, strength, and power to capture a broader spectrum of age-related muscle dysfunction. The primary aims of these analyses are to develop and validate a composite SMFD score and evaluate its association with key geriatric outcome. This study used data from the InCHIANTI follow-up study, involving an initial cohort of 1035 older participants, with a total of 3196 assessments. The SMFD score was computed by assigning quintile-based values of muscle area, density, strength, and lower limb power. Associations with adverse health outcomes, and major chronic diseases were analyzed using mixed-effects models. The SMFD score declined over time from baseline to the third follow-up was: β ± SE:-0.64 ± 0.12 (p-value < 0.001), β ± SE:-1.94 ± 0.13 (p-value < 0.001), and β ± SE:-4.43 ± 0.14 (p-value < 0.001), respectively, and was associated with: BADL (OR = 0.57; 95 %CI: 0.46-0.69), IADL (OR = 0.70; 95 %CI: 0.66-0.75), poor physical performance (SPPB < 7) (OR = 0.68; 95 %CI: 0.64-0.73), Fried's frailty phenotype (OR = 0.72; 95 % CI: 0.68-0.76), hospitalization (OR = 0.96; 95 %CI: 0.93-0.99), and falls' number (OR = 0.96; 95 %CI: 0.92-0.99). Whereas higher SMFD scores were negatively associated with Parkinson's disease, stroke, and hip osteoarthritis. The SMFD score is a valid, multidimensional measure that predicts adverse outcomes in older adults. It holds promise for use in clinical assessment, risk stratification, and targeted interventions.