Self-Reported Fatigue and Its Cross-Sectional Associations with Physical Function throughout Adulthood: The INSPIRE-T Cohort.

Abstract

Fatigue negatively impacts health outcomes but its association with physical function across the adulthood remains unclear. This study described self-reported fatigue levels across age and sex categories, investigated the associations between fatigue and physical functions, and examined whether age and sex moderated their associations. Cross-sectional design. Community. Nine hundred sixteen participants aged 20-100 years in the observational INSPIRE-T cohort study. Participants were classified into four age categories. Fatigue was assessed using the Patient-Reported Outcomes Measurement Information System (Short Form v1.0 - Fatigue 8a) and physical function was assessed by handgrip strength (HGS, Kg), usual gait speed (UGS, m/s), both 5-repetition (5CR, s) and 30-sec chair rise tests (30sCR, times), isokinetic knee extension strength (IKES, N m), and maximum oxygen consumption (V̇O2 max, ml/kg/min). Multiple linear regressions were performed to examine the associations between fatigue and the physical function outcomes (all square-root-transformed). Interactions of fatigue with age and sex were considered. Fatigue levels were the highest in people 75+ years. Women had a higher fatigue level than men. Fatigue was significantly associated with decreasing performance in UGS, HGS, 5CR, and 30sCR but not in IKES and V̇O2 max. Interaction analyses revealed that fatigue was associated with reduced UGS as people age (Fatigue × age: B = -0.002, 95% confidence interval = -0.003, -0.001). Sex did not moderate the association between fatigue and physical function. Our study indicated that fatigue was negatively associated with several components of physical function. Although sex did not moderate the relationship between fatigue and physical function, the association between fatigue and low UGS was more pronounced with increasing age.