Biomechanical Energy Harvesting: Generating Electricity During Walking with Minimal User Effort

TLDR

The device captures energy from negative muscle work during walking, analogous to regenerative braking, rather than relying on positive muscle work as conventional generators do. It is mounted at the knee and activates during the late swing phase to assist joint deceleration. In tests, the harvester produced an average of 5 W—about ten times higher than shoe‑mounted devices—at a metabolic cost less than one‑eighth of conventional generators, making it well suited for charging prosthetic limbs and other portable medical devices.

Abstract

We have developed a biomechanical energy harvester that generates electricity during human walking with little extra effort. Unlike conventional human-powered generators that use positive muscle work, our technology assists muscles in performing negative work, analogous to regenerative braking in hybrid cars, where energy normally dissipated during braking drives a generator instead. The energy harvester mounts at the knee and selectively engages power generation at the end of the swing phase, thus assisting deceleration of the joint. Test subjects walking with one device on each leg produced an average of 5 watts of electricity, which is about 10 times that of shoe-mounted devices. The cost of harvesting—the additional metabolic power required to produce 1 watt of electricity—is less than one-eighth of that for conventional human power generation. Producing substantial electricity with little extra effort makes this method well-suited for charging powered prosthetic limbs and other portable medical devices.