Perceived Physical Fatigability Explains The Association Between Physical Activity And Gait Speed

Abstract

Lower physical activity (PA) and greater perceived physical fatigability (fatigability) contribute independently to slower gait speed. PURPOSE: To fully understand these complex relationships and inform potential interventions, we examined the bidirectional effects between PA and fatigability on gait speed in two generations of older adults (probands and their offspring) enrolled in the Long Life Family Study, a cohort enriched for exceptional longevity. METHODS: At Visit 2 (2014-2017), we measured self-reported PA (typical day over past year) using the Framingham PA Index, perceived physical fatigability with the Pittsburgh Fatigability Scale (PFS, 0-50), and usual gait speed (m/s, fastest of two 4m trials). Linear mixed-effect models (accounting for family relatedness) were used to conduct regressions and mediation adjusted for age, sex, BMI, current smoker, health indicators, depression and field center. RESULTS: At Visit 2, participants (N=2059) ranged in age from 60-107 yrs, with 54.1% female, 99.6% white, PA = 36.6 ± 7.0 MET-hrs/day, PFS = 13.9 ± 9.4, and gait speed = 1.02 ± 0.31 m/s. Compared to offspring (mean ± SD 69.9 ± 6.2 yrs, n=1762), probands were older (92.0 ± 6.9 yrs, n=297), with lower PA, greater PFS scores, and slower gait speed (all p<0.001). Each five MET-hrs/day less PA was directly associated with 0.025 m/s (probands) and 0.005 m/s (offspring) slower gait speed; for fatigability, each five points greater PFS was directly associated with 0.04 m/s (probands) and 0.03 m/s (offspring) slower gait speed (all p<0.001). Further, fatigability explained 41.2% (probands) and 44.4% (offspring) of the effect of less PA on slower gait speed, whereas PA explained 11.0% (probands) and 4.8% (offspring) of the effect of greater fatigability on slower gait speed. CONCLUSIONS: Given that fatigability largely explained PA’s effect on slower gait speed, and the consistency between generations, our findings support fatigability as a potential mediator in the pathway from PA to gait speed. Although we need longitudinal data to confirm the casual directionality, increasing PA may be a likely intervention to reduce perceived physical fatigability and slow the downward spiral leading to worse physical function among older adults. Funded by NIA U01AG023712, U01AG023744, U01AG023746, U01AG023749, U01AG023755.