Skeletal Muscle Function Deficit: An Operational Definition. Results from the InCHIANTI Longitudinal Study

Abstract

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 muscle mass, quality, 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 outcomes in older adults. This study used data from the nCHIANTI study, including 1,035 participants and 3,196 total 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 and was associated with lower risk of BADL (OR 0.57), IADL (OR 0.70), frailty (OR 0.72), poor performance (OR 0.68), hospitalization (OR 0.96), and falls (OR 0.96). Higher SMFD scores were also inversely associated with Parkinson s disease, stroke, and hip osteoarthritis. The SMFD score is a valid, multidimensional measure that predicts adverse outcomes in older adults more effectively than traditional sarcopenia, dynapenia, and powerpenia. It holds promise for use in clinical assessment, risk stratification, and targeted interventions.