Optimizing contact area and joint stiffness of a passive foot-ankle exoskeleton for hopping on deformable terrain

Designing wearable devices for use on deformable terrain is an ongoing engineering challenge. This is particularly apparent when we examine locomotion on dissipative surfaces such as sand or snow. These surfaces have complex, variable dynamics which lead to increased fatigue and metabolic cost during locomotion. We developed a modelling and simulation framework to examine the metabolic energy cost of hopping in sand, with and without a novel, unpowered exoskeletal device. Using this framework, we found that intermediate values of foot contact area and ankle joint stiffness minimize metabolic cost for hopping on sand. This opens up the possibility for a new class of wearable devices that can mitigate the metabolic penalty of moving in complex, dissipative terrain.