Role of Walking Energetics and Perceived Fatigability Differs by Gait Speed: The Study of Muscle, Mobility and Aging (SOMMA).

Background Slower gait speed may be driven by greater energy deficits and fatigability among older adults. We examined associations of walking energetics and perceived physical fatigability with gait speed among slower and faster walkers. Additionally, we used statistical mediation to examine the role of fatigability in the associations of walking energetics and gait speed using the Study of Muscle, Mobility and Aging (SOMMA). Methods Perceived physical fatigability was assessed using the Pittsburgh Fatigability Scale (PFS) Physical score (range 0–50, higher = greater). A 3-phase cardiopulmonary exercise treadmill test collected peak oxygen consumption (VO₂peak, mL/kg/min), energetic cost of walking (EC_W, mL/kg/m), and cost–capacity ratio (VO₂/VO₂peak*100, %). Slower (<1.01 m/s) versus faster (≥1.01 m/s) walkers were classified using median 4-m gait speed. Linear regressions and statistical mediation analyses were conducted. Results Slower walkers had lower VO₂peak, higher EC_W at preferred walking speed (PWS), and greater PFS Physical score compared to faster walkers (all p  < .05; N  = 849). One standard deviation (1- SD) higher VO₂peak was associated with 0.1 m/s faster gait speed, while 1- SD higher EC_W PWS, cost–capacity ratio at PWS and slow walking speed (SWS), and PFS Physical score were associated with 0.02–0.23 m/s slower gait speed. PFS Physical score was a significant statistical mediator in the associations between VO₂peak (15.2%), SWS cost–capacity ratio (15.9%), and EC_W PWS (10.7%) with gait speed and was stronger among slower walkers. Conclusions Slower walkers may be more influenced by perceptions of fatigue in addition to walking energetics. Our work highlights the importance of targeting both energetics and perceived fatigability to prevent mobility decline. [ABSTRACT FROM AUTHOR]