Getting 'under the skin' to examine how exoskeletons steer muscle dynamics during locomotion

Conventional exoskeleton designs for improving human ‘gas-mileage’ rely on motors to transfer net energy from machine to user with the intention of reducing net muscle work and thus, heat loss. In contrast, our design philosophy is that unpowered or minimally powered exoskeletons offer a streamlined way to modify limb-joint morphology in order to steer underling muscle behaviour, rather than transfer energy per se. Indeed, muscles consume energy to fuel force production, modify joint impedance for rejecting disturbances and contain the sensory organs that may be involved in feedback control and motor learning/adaptation during movement. Thus, in anticipation of the ‘diminishing returns’ from powered devices we have focused on developing unpowered systems, inspired by neuromechanical mechanisms borrowed from animals, including humans, that lead to economy during steady locomotion and stability in the face of perturbations.