Animals, including humans, can utilize elastic mechanisms to enhance muscle performance during locomotion. I will present some of our work highlighting how, at distal limb joints such as the ankle, long, compliant series tendon and aponeurosis can decouple joint and muscle displacements — allowing muscles to operate at lengths and velocities that are favorable for economical force production, (i.e., during steady movements like constant speed running) or high power outputs (i.e., during accelerative movements like maximum distance jumps).
Then, I will describe how we translated our understanding of elastic mechanisms to build a passive elastic exoskeleton and novel clutching mechanism that can provide ‘a spring in your step’ by storage and release of elastic energy in a parallel elastic element worn about the ankle (i.e., an exo-tendon) during human walking. This device can reduce the metabolic cost of walking by ~7% below normal without adding any external energy from batteries or motors. We contend that simple, bio-inspired designs promise more functional assistive technology than current passive AFO product lines; and could provide a cheaper, more practical alternative to fully powered lower-limb exoskeletons now coming to market.
Finally, I will introduce the idea of mechanical resonance as a guiding principle that can be used to inform modifications in the structure of the human foot-ankle system to achieve desired functional outcomes during locomotion. Using healthy aging as a case study, I will motivate the potential for elastic ankle exoskeletons to ‘re-tune’ the structure and function of the plantarflexors in order to improve walking performance later in life.
If there is time, I will briefly touch on some exciting new work using isolated muscle-tendons (e.g., an in situ rat preparation) in combination with a novel, benchtop bio-robotic interface to explore the fundamental rules of optimal neuromechanical interaction in hybrid bio-robotic systems.