Role of Walking Energetics and Perceived Fatigability on Mobility Differ by Walking Speed: The Study of Muscle, Mobility and Aging (SOMMA)

BackgroundSlow gait speed is a risk factor for poor health outcomes among older adults and may be driven by decreased energy availability and increased fatigability. ObjectiveExamine walking energetics and perceived physical fatigability with gait speed among slower and faster walkers and understand whether fatigability statistically mediates the association between energetics and gait speed. MethodsPerceived physical fatigability was assessed using the Pittsburgh Fatigability Scale (PFS) Physical score (range 0-50, higher=greater). A three-phase cardiopulmonary exercise treadmill test collected peak oxygen consumption (VO2peak mL/kg/min), energetic cost of walking per distance travelled (ECW, mL/kg/meter), and cost-capacity ratios (VO2/VO2peak, %). Gait speed was determined by 4m walk; slower (<1.01m/s) vs faster ([&ge;]1.01m/s) walkers were classified using median 4m gait speed. Linear regressions and statistical mediation analyses were conducted. ResultsSlower walkers had lower VO2peak, higher ECW at preferred walking speed (PWS), and greater PFS Physical score compared to faster walkers (all p<0.05) (N=849). One standard-deviation higher increment of VO2peak, ECW at PWS, cost-capacity ratios at PWS and slow walking speed (SWS), and PFS Physical score were associated with 0.1m/s faster (VO2peak only) or 0.02-0.09m/s slower gait speed. PFS Physical score was a significant statistical mediator in the associations between VO2peak (15.2%), cost-capacity ratio (15.9%), and ECW at PWS (10.7%) with gait speed, and stronger among slower walkers. ConclusionsFitness and fatigability are associated with slower gait speed yet contributions may differ among slower and faster walkers. Future interventions may consider targeting fatigability among slower walkers and fitness among faster walkers.