Scientists at Carnegie Mellon University, North Carolina State University, and the University of North Carolina at Chapel Hill recently developed a wearable exoskeleton that reduces the energy used in walking.
A new exoskeleton has been developed to reduce energy people use while walking.
Source: Wikimedia Commons
The researchers describe this exoskeleton as a “lightweight elastic device that acts in parallel with the user’s calf muscles” (1). This exoskeleton works to lower the metabolic energy needed for the muscle to contract. Its key element is a “mechanical clutch [used] to hold a spring as it is stretched and relaxed by ankle movements when the foot is on the ground” (1).
What makes this device especially novel is that it requires no energy to function. The authors elaborate on this novelty by noting, “the exoskeleton consumes no chemical or electrical energy and delivers no net positive mechanical work, yet reduces the metabolic cost of walking by approximately 7.2% for healthy human users under natural conditions, comparable to savings with powered devices” (1).
The researchers’ main goal was to reduce the metabolic energy used by humans to walk. Humans on average walk 10,000 steps each day, and “people expend more energy during walking than any other activity of daily life” (1). Still, walking is an activity not typically associated with excess energy consumption. The scientists understand that, claiming “herein lies the challenge: reducing the effort of normal walking could garner substantial benefits, but humans are already so energy-effective that making improvements is extremely difficult” (1).
They chose to attack this problem not simply by adding or subtracting to the body’s natural movements, but by changing the way the body operates while walking. They created the exoskeleton to be a lightweight (between 0.408 and 0.503 kilogram (kg)) extension of the calf muscles and tendons that “uses more efficient structures” for performing movements (1). This works because there is a “metabolic cost on body weight support and on holding tendons as they stretch and recoil” (1).
As previously mentioned, the exoskeleton is composed of a spring and a clutch. The spring works in tandem with the Achilles tendon, and the clutch “engages the spring when the foot is on the ground and disengages it to allow free motion when the foot is in the air” (1). Crucially, the device does not restrict normal ankle movements despite the fact that it is hinged at the ankle.
The researchers tested the effectiveness of the exoskeleton on nine participants, who wore one exoskeleton on each leg, and who walked at a speed of approximately 1.25 meters per second (1). They found that the device worked best to decrease metabolic energy usage when springs of a moderate stiffness were used (1). The best spring resulted in a “metabolic cost of walking” of 2.67 ± Watts per kg (the “cost” without the device) (1). the researchers equated this improvement to “the effect of taking off a 4 kg [roughly 8.8-pound] backpack for an average person” (1).
Sources:
- Collins, S. H., Wiggin, M. B., & Sawicki, G. S. (2015). Reducing the energy cost of human walking using an unpowered exoskeleton. Nature, advance online publication. http://doi.org/10.1038/nature14288