Fat mass but not fat-free mass is related to physical capacity in well-functioning older individuals: nutrition as a determinant of successful aging (NuAge)--the Quebec Longitudinal Study.

BACKGROUND: Aging is associated with increases in fat mass (FM) and decreases in fat-free mass (FFM) that may affect physical capacity. However, it is not clear whether high FM or low FFM contribute more to a reduction in physical capacity.
METHODS: A structural equation modeling strategy was used to test an explanatory model of the association between body composition and physical capacity. The concept of physical capacity was assessed by walking speed at a normal pace and the one leg stand test. To test the model, 904 men and women between 67 and 84 years old were studied. Body composition was measured by dual-energy x-ray absorptiometry (DXA). Confounding factors related to body composition and physical capacities were included in the explanatory model (physical activity level, age, gender, and number of reported diseases).
RESULTS: The final model showed that physical capacity can be represented by a factorial first-order model including generic measures of walking speed and balance. Moreover, our results showed that percentage of FM was significantly associated with physical capacity (p<.01), whereas no such association was observed with FFM. Other variables such as physical activity level, number of self-reported diseases, and age were associated with physical capacity (all p<.01). Overall, the proposed model explained 48% and 57% of the variance observed in men and women when using the one leg stand and the walking speed at normal pace tests as measures of physical capacity.
CONCLUSION: FM was significantly and inversely correlated with physical capacity, whereas FFM was not associated when controlled for other potential confounding variables. More studies are needed to investigate the effect of different levels of obesity on physical capacity in older individuals.