Identifying invariant gait metrics for exoskeleton assistance

Exoskeletons have the potential to increase the independence and quality of life of patients with walking pathologies. To do this effectively, the exoskeleton requires a control paradigm that can determine the timing and magnitude of assistance that is suitable for the user's task and environment. This paper searches for a metric that can be optimised, enabling assistance to be applied without compromising the energy efficiency and stability of gait. Spatial and temporal, kinematic, kinetic, and other novel dynamic stability metrics were compared across three different assistance scenarios and five different walking contexts. Results demonstrated that three metrics: step width, medial-lateral centre of pressure displacement, and medial-lateral margin of stability were the most invariant. This result suggests dynamic stability metrics are optimised in human gait and therefore are potentially suitable metrics for optimising in an exoskeleton control paradigm.