Unilateral exoskeleton assistance lowers metabolic cost in human walking Authors: Pieter Van den Berghe, Philippe Malcolm, Samuel Galle, Dirk De Clercq Department of Movement and Sports Science, Ghent University, Belgium Abstract Introduction Exoskeletons exists for i.a. reducing metabolic cost, but often the ankle joint is neglected. Our ankle-foot exoskeleton reduced metabolic cost via optimal bilateral push-off timing.1 However, push-off work was not held constant, which influences metabolic cost.2 Unilateral exoskeleton assistance could be useful for restoring symmetry in pathologies with unilateral impairments (e.g. hemiplegia). As a first step towards clinical use of unilateral assistance we wanted to study the effects of unilateral assistance and asymmetry in healthy subjects. Methods 13 healthy adults (♂) walked with an ankle-foot exoskeleton that can assist plantarflexion [2]. The experiment consisted of unilateral or bilateral assistance in 9 conditions of various push-off timings (35, 43, 50 stride%) and work rates (maximal, half). Unpowered walking acted as control. Conditions were randomized. Metabolic cost was determined via indirect calorimetry. Trials were compared using RM ANOVA (α=0.05). Figure 1. Net metabolic cost vs. timing-power conditions. Unilateral = striped; bilateral = full-colored bars. Values are means ± SD. Results Figure 1 shows net metabolic cost reduction in all conditions (p < 0.01), with larger bilateral (-11 till -15%) than unilateral (-6 till -9%) reductions. Power variations in the bilateral trials resulted in equal energetic demands. However, low power gave the highest reduction normalized versus work rate. Dominant and non-dominant unilateral leg assistance did not differ. Discussion Results concur with previous exoskeleton experiments, although the optimal timing was earlier than the existing guideline (~43%).1 Heavier subjects and a larger exoskeleton maybe led to different work profiles that could have altered the optimum. Conclusions Push-off timing and mechanical work rate seem crucial elements for a more efficient gait. Leg dominance does not seem to interact with metabolic consumption through unilateral ankle support in the abled-bodied. Vervolg artikel in nummer 2. nummer 1 | maart 2015 | Sport & Geneeskunde 49 Pagina 48
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Sport & Geneeskunde nummer 1 | maart 2015 Lees publicatie 45Home