Factor analysis to determine relative contributions of strength, physical performance, body composition and muscle mass to disability and mobility disability outcomes in older men

Background: It is not known how measures of body composition, strength and physical performance are interrelated or how empirical groupings of these measures relate to disability and mobility disability. Methods: Muscle mass was assessed by D3-creatine dilution (D3Cr muscle mass) in 1345 men (84.1 ± 4.1 years) enrolled in the Osteoporotic Fractures in Men (MrOS) study. Participants completed anthropomorphic measures, walk speed, grip strength, chair stands, and dual x-ray absorptiometry (DXA) estimated appendicular lean mass (ALM) and body fat percentage. Men reported limitations in mobility, activities of daily living (ADLs) and instrumental ADLs at initial and over 2.2 ± 0.3 years. Factor analysis reduced variables into related groups and negative binomial models calculated relative risk (RR) of factors with mobility and disability outcomes. Results: Factor analysis reduced 10 variables into four factors: Factor 1, body composition, including ALM, body fat percentage, weight and muscle mass; Factor 2, body size and lean mass, including height, weight and ALM; Factor 3, muscle mass, strength and performance, including walk speed, chair stands, grip strength, and muscle mass; and Factor 4, lean mass and weight, including ALM and weight. Only Factor 3 was significantly associated (p-value < .001) with prevalent disability (RR per standard deviation increment in factor score (reflecting higher muscle mass, strength and physical performance) 0.44, 0.35–0.56) and mobility disability (RR 0.22, 0.17 0.28), and incident mobility disability (RR 0.37, 0.27–0.50). Conclusion: D3Cr muscle mass was the only body composition variable that co-segregated with strength and physical performance measures, and contributed to a factor that was associated with disability outcomes in older men.