Evaluation of Lower Leg Muscle Activities During Human Walking Assisted by an Ankle Exoskeleton

Abstract

Wearable robots like ankle exoskeletons have demonstrated the capability to enhance human mobility and to reduce biological efforts of human locomotion. The type of assistance provided by ankle exoskeletons could influence the lower leg muscle activities during human walking. This article aimed to systematically evaluate the lower leg muscle activities under different ankle exoskeleton assistance conditions. We measured multiple electromyography-based metrics of five lower leg muscles, while the participants walked with an ankle exoskeleton on a treadmill. Nine assistance conditions, which combined three peak times (46%, 49%, and 52% of stride time) and three peak torque levels (0.3, 0.5, and 0.7 N $\cdot$ m $\cdot$ kg $^{-1}$ ), are applied to assist plantarflexion during ankle push-off. Nine healthy subjects participated in the experiments. Of all investigated muscles, the activity level of l.SOL is influenced the most when exoskeleton assistance is applied. The root mean square of l.SOL activity reduces by 33.6 $\pm$ 14.0% under one assistance condition compared to walking without the exoskeleton. Our results can be used to guide studies on mechanical and control designs to improve neuromuscular interactions between exoskeletons and wearers.