Clustering of strength, physical function, muscle, and adiposity characteristics and risk of disability in older adults.

OBJECTIVES: To empirically identify groupings of strength, physical performance, adiposity, and lean mass and test how such groupings of these interrelated measures may relate to disability risk.
DESIGN: Prospective Health, Aging and Body Composition Study.
SETTING: Two U.S. clinical centers. PARTICIPANTS: One thousand two hundred sixty-three women and 1,221 men. MEASUREMENTS: Weight, strength (knee extension, grip); walking speed, chair stands, dual X-ray absorptiometry (fat and lean mass for total body, arm, and leg; percent fat), and thigh computed tomography scans (muscle area, muscle density). Analyses were stratified according to sex. Factor analysis reduced these variables into a smaller number of components, and proportional hazards models assessed risk of major disability for the components identified.
RESULTS: In both sexes, factor analysis reduced the 14 individual variables into three components that explained 76% to 77% of the data variance: Factor 1, an adiposity component, with strong loading by fat mass, weight, and muscle density; Factor 2, a strength and lean body size component with strong loading by lean mass, weight, and strength; Factor 3, a physical performance component with positive loading by walking speed and chair stand performance. Factor 1 (adiposity) and Factor 3 (performance) but not Factor 2 (strength and lean body size) were associated with disability over 6.1 ± 2.6 years.
CONCLUSION: The adiposity and physical performance constructs but not the strength and lean body size construct were associated with disability risk, suggesting that adiposity and performance should be considered as risk factors for disability.