Removing energy with an exoskeleton reduces the metabolic cost of walking

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Store energy and save energy
Many devices have been developed to harvest energy from walking or running, but their use often comes at cost to the wearer in the form of increased metabolic demand. Shepertycky et al. designed a device that can harvest mechanical energy from a natural walking gait and convert it to useable electrical energy while also reducing the metabolic energy consumption of the user (see the Perspective by Riemer et al.). The key to achieving “something from nothing” comes from designing the device to use muscle-centric control of the knee exoskeleton resistance to reduce active muscle force during the late part of the leg swing cycle.

Science, aba9947, this issue p. 957; see also abh4007, p. 909

Abstract
Evolutionary pressures have led humans to walk in a highly efficient manner that conserves energy, making it difficult for exoskeletons to reduce the metabolic cost of walking. Despite the challenge, some exoskeletons have managed to lessen the metabolic expenditure of walking, either by adding or storing and returning energy. We show that the use of an exoskeleton that strategically removes kinetic energy during the swing period of the gait cycle reduces the metabolic cost of walking by 2.5 ± 0.8% for healthy male users while converting the removed energy into 0.25 ± 0.02 watts of electrical power. By comparing two loading profiles, we demonstrate that the timing and magnitude of energy removal are vital for successful metabolic cost reduction.

https://science.sciencemag.org/content/372/6545/957

“Removing energy from a person's legs during walking may sound counterintuitive, like applying the brake in a moving car,” says Michael Shepertycky, a recent PhD graduate and lead author of the study, “but our muscles naturally remove energy while we walk, and our device helps them to do so.”

https://engineering.queensu.ca/news/2021/05/unique-technology-gives-humans-a-leg-up-on-walking.html