Metabolic adaptation and related biomechanics in an ankle-based exoskeleton system during six sessions of steady state walking.

Ankle-based exoskeletons have demonstrated metabolic benefits during steady-state walking; however, variability exists in individual adaptation timelines necessary to achieve those benefits. This study assessed timelines for metabolic and gait-related adaptation while wearing an ankle-based exoskeleton while powered (EXOP) compared to unpowered (EXNP) and no device worn (NOEX). Metabolic (VO₂) and biomechanics data were collected while 14 participants walked on a treadmill at 1.3 m/s for six sessions. To better understand variability in responses to wearing exoskeletons, the cohort was divided based on the slope of the VO₂ response of the first two sessions in the EXOP condition, and gait parameters were compared between subgroups. Repeated measures analyses of variance revealed a significant (p ≤ 0.001) 10% VO₂ reduction for EXOP compared to EXNP and a non-significant 2.5% reduction for EXOP v NOEX. Lack of significant session-based comparisons indicated no additional VO₂ adaptation; however, significant session-related results for peak knee flexion (interaction, p = 0.042) and step width (session main effect, p = 0.003) suggest gait-related adaptation continued during the sessions. Subgroup results indicated different response profiles to wearing exoskeletons; and implications of classifying initial responses based on metabolic response are discussed as an approach to understand what drives variation in responses to these devices.