Role of Fatigue on the Effectiveness of a Physical Activity Intervention Aimed at Preventing Mobility Disability

Abstract

While physical activity (PA) is known to preserve mobility and functional capacity in older adults, greater self-reported fatigue is associated with slower gait speed and poorer mobility. The potential impact of initial fatigue levels in mitigating the effects of a physical activity intervention on major mobility disability (MMD) outcomes has yet to be explored. PURPOSE: To examine the impact of a PA intervention on the risk of MMD by baseline (BL) fatigue status in older adults at risk for mobility disability. METHODS: The Lifestyle Interventions and Independence for Elders (LIFE) Study was a randomized clinical trial of a structured, moderate-intensity PA program (mean duration=2.6 years) consisting primarily of walking compared to a successful aging health education (SA) program in 1635 older adults, mean age 78.9±5.2 years. Self-reported fatigue was assessed using the Trait version of the Exercise-Induced Feelings Inventory (EFI-T), a 6-item scale with each item scored 0 (none of the time) to 5 (all of the time). A total score was calculated by averaging the items and the median split was used to define BL fatigue status: higher fatigue ≥2 (N=876) and lower fatigue <2 (N=755). A usual-paced 400m walk was conducted every 6 months; MMD was defined as the loss of ability to walk the 400m within 15 min. Cox proportional hazard models were used for the analysis of MMD in the PA vs. SA groups according to baseline fatigue status. RESULTS: Time to walk 400m at BL was slower for those with higher fatigue (521.0±113.3 sec) compared to lower fatigue (494.6±112.8 sec), p<0.0001. Participants with higher BL fatigue who were randomized to the PA program had a 26% lower risk of MMD compared to those who self-reported higher BL fatigue in SA (hazard ratio [HR] 0.74 [95% CI, 0.59-0.92], p=0.006). For those with lower BL fatigue, there was no difference between intervention programs on MMD (HR 0.88 [95% CI, 0.66-1.17], p=0.39); p-value for BL fatigue by intervention interaction: 0.24. Results did not change after adjustment for BL 400m walk time. CONCLUSION: A long-term moderate intensity PA intervention may be particularly effective in preserving mobility in older adults at risk for MMD who self-reported higher levels of initial fatigue. Supported by U01AG22376 from the NIH.