Effects of Ankle Exoskeleton Motor Location on Gait Biomechanics and User Perceptions: The Bowden Cable Dilemma

Motor-powered ankle exoskeletons have been shown to improve walking and rehabilitation outcomes in individuals with and without gait impairments (e.g., cerebral palsy (CP)). To date, ankle exoskeleton designs have either placed the motors on the shanks (direct or quasi-direct drive) or around the waist with Bowden cable transmissions. The former offers better transmission efficiency, while the latter reduces added mass biomechanical penalty. The biomechanical effects of motor placement may be magnified for individuals with CP due to weakened lower limb strength. To date, no study has compared how motor placement alters the biomechanical responses and user perceptions of individuals with or without gait impairment (e.g., CP). In this study involving 7 individuals with CP and 9 unimpaired individuals, we compared their metabolic cost of transport, lower limb muscle activities, and user perceptions when using ankle exoskeletons with either waist-mounted motors (and Bowden cables) or shank-mounted motors that were otherwise identical. Despite changes in lower leg muscle recruitment, results showed no statistical differences in the metabolic cost of transport. Shank-mounted motors were preferred by more participants in both cohorts (e.g., 6/7 in CP). These results help inform the ergonomics and mechanical designs of ankle exoskeletons and how they may be perceived.