A simple ankle-foot exoskeleton can lower the metabolic cost of walking

Robotic exoskeletons can assist plantarflexion by means of pneumatic actuators. Most experiments make use of exoskeletons with proportional myoelectric control (P.M.C.), which is believed to cause the greatest reduction in metabolic power. An ankle-foot exoskeleton controlled by switches in the heel (footswitch control) was developed in our lab. We hypothesized that this active exoskeleton (powered) could lower the metabolic cost of both level and uphill (15%) walking compared to walking with an inactive exoskeleton (unpowered). A 16% reduction (0.70 W kg-1) in net metabolic power was found between powered and unpowered (level) walking during a habituation trial. During uphill walking the active exoskeleton caused a reduction of 13% (1.46W kg-1) in net metabolic power. Subjects were metabolically adapted after 17.5 min of walking with the exoskeleton, which is faster than in other experiments using P.M.C. Furthermore we found reductions in metabolic power after only 2 min of exoskeleton walking. Because of the simplicity of an exoskeleton with footswitch control and the fast reductions in metabolic power, this type of exoskeleton is supposed to have an opportunity to become a useful tool in locomotion research, and possibly as a mobility aid