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

ABSTRACT

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.

After initial training, VO2 reductions were observed with an ankle-based exoskeleton during the initial session and those reductions were maintained for the remaining sessions. Some gait-related variables continued to change over the remaining sessions. Exploratory work based on differences between early metabolic responses revealed potential adaptation strategy subgroups.