Sex impacts the relation between body composition and physical function in older adults

Objective: To determine the sex-specific relationships between physical activity, aerobic fitness, adiposity (%Fat), mineral-free lean mass (MFLM), and balance and gait performance in older adults. Methods: Eighty-five female and 49 male sedentary, healthy, community-dwelling older adults (mean [SD] age, 69.6 [5.4] and 70.3 [4.7] years, respectively) were evaluated on habitual physical activity via questionnaire, aerobic fitness by a maximal oxygen consumption treadmill test, whole and regional body composition by dual-energy x-ray absorptiometry, and lower extremity physical function using gait tasks and computerized dynamic posturography. Results: As expected, men had less body fat, more lean mass, and higher aerobic fitness than did women and tended to perform better on all lower extremity physical function tasks (all P <= 0.1). Physical activity was not related to gait; however, fitness was related to gait in both sexes (r > 0.50, all P < 0.05). Body fat was related to gait in women (r = -0.38, P < 0.05) but not in men. Neither fitness nor body composition was related to balance in men, whereas in women, leg MFLM was positively associated (r = 0.27, P < 0.05). Women, but not men, with a greater ratio of body weight to leg MFLM performed worse on gait tasks (P < 0.001). There was an interaction with sex for %Fat on gait (P = 0.05) and for leg MFLM on balance (P < 0.05). Conclusions: In sedentary healthy older adults, the relation between body composition, aerobic fitness, and balance and gait differs between sexes such that women are more strongly affected by alterations in body composition. Lower %Fat and preservation of lower body lean mass have important implications for reducing the risk of physical disability, especially in older women.