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When we typically think of the word “exoskeleton“, images of creepy, crawly cockroaches and seaside crabs and lobsters come to mind. This external skeleton functions to protect and support the animal, much like our own internal skeleton does. New research, published in Nature, provides an alternate way to think about exoskeletons. In an effort to find a way to reduce the energy cost of walking, mainly for the benefit of the aging or disabled populations, researchers from North Carolina State University and Carnegie Mellon University have developed an unpowered exoskeleton for human use.

Although humans have evolved to increase efficiency and constantly strive to minimize energy consumption by optimizing step length and arm movements, people still spend more of their daily energy walking than on any other activity. Our ankle joints act as the body’s major power source to get us from point A to point B by enabling up-and-down movements of the foot. The elastic, plastic exoskeleton, as designed by the researchers acts to make walking easier and helps increase stability.

Once researchers found that the calf muscle and Achilles tendon are used as clutches, not muscles, for movement, they decided to recreate this clutch system outside of the body. Essentially, this clutch acts in the same manner as a car clutch. The clutch is a mechanical device that stores power and determines whether to pass it on. In cars, the clutch stores power from the engine and can pass this power along to the wheels. In humans, the calf muscle and Achilles tendon store energy instead.

 Walking is a source of major energy usage.

Image Source: Andy Bullock

The exoskeleton structure made by researchers is similar to a boot. Running down the backside of each leg, a passive clutch mechanism and a spring act to recreate the calf-Achilles tendon relationship. When a user places his or her heel on the floor and extends the leg to move forward, the spring stretches and stores energy. Alternatively, when the ankle leaves the ground, the spring recoils and the energy that was stored within the spring is used to minimize the metabolic energy required in this portion of the walking cycle.

The clutch requires no energy input, yet it reduces energy cost by seven percent. If this does not seem significant, imagine that putting this extra spring in your step offsets the forces generated by a ten-pound backpack. By acting as a catapult, so to speak, this device reduces strain on the calf muscles. By reducing force placed on our muscles, we can save precious metabolic energy.

This study was conducted on a small sample of only 10 individuals; however, the results look extremely promising. The hope is that this device will help improve the quality of life for many, including the general aging population, individuals readjusting to walking

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