Muscle fatigability and depressive symptoms in later life

Objective: Fatigability is the degree to which performance decreases during a specific activity of a given intensity and duration. Depression is known to heighten subjective fatigue, but whether its association with physical fatigability is unknown. Further, whether fatigability is a precursor or risk factor for the development of subsequent depressive symptoms is also unclear. Methods: Data are from the Health Aging and Body Composition Study with fatigability assessed using isokinetic dynamometry of the knee extensors at year 3, and depressive symptoms ascertained longitudinally using the Center for Epidemiologic Studies Depression (CES-D) scale. The relationship between fatigability and depressive symptoms was evaluated using linear and Cox regression models. Results: There was a significant cross-sectional association between fatigability and depressive symptomatology (β = −0.06, p = 0.02), after adjusting for demographic variables, medical comorbidities, cognition, gait speed, and physical activity levels. Greater fatigability was associated with greater adjusted scores on the 10-item CES-D (F_{2, 1695} = 38.65, p < 0.001), with individuals with greater fatigability on average reporting an adjusted CES-D score 0.5 point greater than those individuals with higher levels of resistance to fatigability (mean of 70% or better; p < 0.001). Fatigability however was not associated with the development of depression at follow-up (p = 0.828). Conclusions: This study found an association between skeletal muscle fatigability and higher depressive symptoms in older adults, but no longitudinal association was identified. These findings suggest that age-related changes in energy capacity may affect the phenomenology of late life depression.