Towards efficient lower-limb exoskeleton evaluation: defining biomechanical metrics to quantify assisted gait familiarization

Biomechanical evaluation of exoskeletons is a fundamental part of testing hardware and software modifications, but it can be quite challenging and inefficient since different users demonstrate different familiarization patterns and time windows. In this paper, we define four biomechanical metrics that serve as gait familiarization indicators for lower-limb exoskeleton assistance, in order to increase the efficiency and accuracy of biomechanical measurements and data collection, for exoskeleton testing. We assess stride duration, mediolateral deviation from a straight path, polygon of support area, and muscle effort of the lower and upper body, for five participants performing five walking bouts with a manual and a more automatic mode of exoskeleton each. We observed familiarization trends only under the automatic mode for the latter five bouts, based on the reduction of the quantities of the first three metrics (p < 0.05). Muscle effort showed evidence of familiarization based on reductions of co-contraction for the arms only, while muscle activity did not show any familiarization trends for lower or upper body muscles. This study demonstrated that the first three biomechanical metrics are promising candidates for familiarization indicators and thus paves the path towards more efficient exoskeleton testing.