The dual timescales of gait adaptation: initial stability adjustments followed by subsequent energetic cost adjustments.

Gait adaptation during bipedal walking allows people to adjust their walking patterns to maintain balance, avoid obstacles and avoid injury. Adaptation involves complex processes that function to maintain stability and reduce energy expenditure. However, the processes that influence walking patterns during different points in the adaptation period remain to be investigated. We assessed split-belt adaptation in 17 young adults aged 19-35. We also assessed individual aerobic capacity to understand how aerobic capacity influences adaptation. We analyzed step lengths, step length asymmetry (SLA), mediolateral margins of stability, positive, negative and net mechanical work rates, as well as metabolic rate during adaptation. Dual-rate exponential mixed-effects regressions estimated the adaptation of each measure over two timescales; results indicate that mediolateral stability adapts over a single timescale in under 1 min, whereas mechanical work rates, metabolic rate, step lengths and SLA adapt over two distinct timescales (3.5-11.2 min). We then regressed mediolateral margins of stability, net mechanical work rate and metabolic rate on SLA during early and late adaptation phases to determine whether stability drives early adaptation and energetic cost drives late adaptation. Stability predicted SLA during the initial rapid onset of adaptation, and mechanical work rate predicted SLA during the latter part of adaptation. Findings suggest that stability optimization may contribute to early gait changes and that mechanical work contributes to later changes during adaptation. A final sub-analysis showed that aerobic capacity levels <36 and >43 ml kg-1 min-1 resulted in greater SLA adaptation, underscoring the metabolic influences on gait adaptation. This study illuminates the complex interplay between biomechanical and metabolic factors in gait adaptation, shedding light on fundamental mechanisms underlying human locomotion.