How Ankle Exoskeleton Assistance Affects the Mechanics of Incline Walking and Stair Ascent in Cerebral Palsy.

Abstract

Graded terrains, like slopes and stairs, are particularly challenging for people with neurological disorders like cerebral palsy (CP) due to increased selective muscle control and muscle strength requirements. Lower-limb exoskeletons may be able to assist individuals with CP when navigating graded terrains. This study sought to determine the effects of untethered ankle exoskeleton assistance on lower-limb joint angles, moments, and muscle activity during up-incline walking and up-stair stepping in CP (n=7). We hypothesized that powered assistance would result in improved ankle mechanics (i.e., increased total ankle moments) across both terrains. During incline walking, we found that peak ankle dorsiflexion angle increased by $7^{\mathrm{o}}$(p=0.006) during walking with ankle assistance compared to walking without the device (Shod). Compared to without the device, the peak total ankle plantarflexor moment increased by 8% (p=0.022) while peak biological ankle plantarflexor moment decreased by 17% (p< 0.001). Incline walking with ankle assistance reduced stance phase muscle activity of the soleus (20%, p=0.010) and vastus lateralis (18%, p=0.004), and swing phase tibialis activity (19%, p=0.028) compared to Shod. During stair ascent with the device, the peak total ankle plantarflexor moment increased by 17% (p=0.011) and the peak knee extensor moment increased by 40% (p=0.018) compared to Shod. These findings provide insight into the biomechanical benefits of ankle exoskeleton assistance during incline and stair walking. This work aims to advance the use of robotic assistive technology to improve mobility for people with CP.