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Objective: To determine the relative contributions of adiposity and muscularity to multi-dimensional performance-based and perceived physical function in older adults living independently.

Methods and Procedures: Data from 109 women and men, aged 60 or older, with low serum dehydroepiandrosterone (DHEA) sulfate levels were included in this cross-sectional analysis of baseline measures from a single-site, randomized, controlled trial of DHEA replacement therapy. Physical function was determined by means of performance on the 100-point Continuous Scale-Physical Functional Performance (CS-PFP) test and by self-reporting using the physical function subscale of the Medical Outcomes Short Form-36 (SF36PF). Body composition was measured by dual-energy X-ray absorptiometry (DXA). Linear regression analyses were used to determine the contributions of body mass index (BMI; kg body mass/m2), fat index (FI; kg fat/m2), and appendicular skeletal muscle index (ASMI; kg muscle/m2) to the CS-PFP and SF36PF scores, adjusted for age and sex.

Results: Age-adjusted regression analyses indicated that FI, but not ASMI, was a significant (P < 0.001) determinant of CS-PFP (R 2 = 0.54) and SF36PF (R 2 = 0.37). When adjusted for age and sex, BMI was nearly as good a predictor of CS-PFP (R 2 = 0.50) and SF36PF (R 2 = 0.34) as FI.

Discussion: Adiposity was a stronger predictor of measured and self-reported physical function than was muscularity in older adults living independently. BMI, adjusted for sex, is a reasonable substitute for adiposity in the prediction of physical function.