Reducing the energy cost of human walking using an unpowered exoskeleton

By Steven H. Collins, M. Wiggin, Gregory S. Sawicki. Nature, 2015

942 citations recorded by the source corpus.

With efficiencies derived from evolution, growth and learning, humans are very well-tuned for locomotion. Metabolic energy used during walking can be partly replaced by power input from an exoskeleton, but is it possible to reduce metabolic rate without providing an additional energy source? This would require an improvement in the efficiency of the human–machine system as a whole, and would be remarkable given the apparent optimality of human gait. Here we show that the metabolic rate of human walking can be reduced by an unpowered ankle exoskeleton. We built a lightweight elastic device that acts in parallel with the user's calf muscles, off-loading muscle force and thereby reducing the metabolic energy consumed in contractions. The device uses a mechanical clutch to hold a spring as it is stretched and relaxed by ankle movements when the foot is on the ground, helping to fulfil one function of the calf muscles and Achilles tendon. Unlike muscles, however, the clutch sustains force passively. The exoskeleton consumes no chemical or electrical energy and delivers no net positive mechanical work, yet reduces the metabolic cost of walking by 7.2 ± 2.6% for healthy human users under natural conditions, comparable to savings with powered devices. Improving upon walking economy in this way is analogous to altering the structure of the body such that it is more energy-effective at walking. While strong natural pressures have already shaped human locomotion, improvements in efficiency are still possible. Much remains to be learned about this seemingly simple behaviour.

Subfields: Biomedical Engineering

View Paper: https://www.semanticscholar.org/paper/8399246848b70722594100c7981d6661957daa56

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In Biomedical Engineering

Citations in the corpus

State of the Art and Future Directions for Lower Limb Robotic Exoskeletons (2017, background): “Another recent ankle exoskeleton device has achieved a reduction in metabolic energy consumption for walking without any powered assistance at all [39].”
Human-in-the-loop optimization of hip assistance with a soft exosuit during walking (2018, background): “Recent breakthroughs in wearable robotics have substantially reduced energy expenditure in human walking using both passive (1) and active autonomous (2–4) or tethered (5–11) devices.”
The exoskeleton expansion: improving walking and running economy (2020, background): “…8 7 Ankle Autonomous Active Walk 1.5 Level Ground 4 Load Carry (23 kg) 4 L Mooney 2014b 10 7 Ankle Autonomous Active Walk 1.4 Level Ground 3.6 5 S Collins 2015 7.2 9 Ankle Autonomous Passive Walk 1.25 Level Ground 0.91 6 L Mooney 2016 11 6 Ankle Autonomous Active Walk 1.4 Level Ground 3.6 7 K…”
Fluid-driven origami-inspired artificial muscles (2017, background): “This technique allows us to quickly program, fabricate, and implement actuation systems for very specific working environments at multiple scales, such as active metamaterials (44), miniature surgical devices (45, 46), wearable robotic exoskeletons (47), transformable architecture, as well as deep-s”
Assistance magnitude versus metabolic cost reductions for a tethered multiarticular soft exosuit (2017, result): “The fact that we did not see diminishing returns of metabolic reduction with increasing assistance differs from other parameter sweep studies with ankle assistive devices (exoskeletons and prostheses), which found either a leveling off or increase in metabolic rate (13, 14, 22, 23).”