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Without using any power, this leg-mounted exoskeleton makes walking more efficient

Ever since our ancestors started walking upright, we humans have evolved to become extremely efficient walkers. In fact, simulations of human locomotion show that walking at a constant speed across level ground should theoretically require almost no power input at all; but anyone who works on their feet or has gone on a hike knows otherwise. For some reason, walking is more difficult than it should be — but engineers are beginning to figure out ways to fix that.

According to a recent study published in Nature, researchers at Carnegie Mellon and North Carolina State have developed a leg-mounted exoskeleton that has been shown to reduce the metabolic cost of walking by around 7 percent — without using any motors or electricity.

To achieve this, the researchers had to first gain a more detailed understanding of how human locomotion works. After years of studying the biomechanics of walking, Steve Collins and Greg Sawicki discovered that the calf muscle not only exerts energy when pushing a person forward, but also when performing a clutch-like action to hold the Achilles tendon taut.

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“Studies show that the calf muscles are primarily producing force isometrically, without doing any work, during the stance phase of walking, but still using substantial metabolic energy,” Collins explained. “This is the opposite of regenerative braking. It’s as if every time you push on the brake pedal in your car, you burn a little bit of gas.”

To remedy this inefficiency, the duo constructed an ingenious mechanical system that reduces the work your calf does while you walk. Here’s how:

Each carbon-fiber frame features a spring that connects the back of the foot to just below the back of the knee, where it attaches with a mechanical clutch. When the user’s Achilles tendon is being stretched, the clutch is engaged and the spring — working like an additional tendon– stretches and helps to store energy. After the standing leg pushes down, unleashing elastic energy, the clutch releases and absorbs the slack in the spring in preparation for the next cycle.

The only downside (as you can see in the video) is that you sound like a poorly-oiled robot while you walk, and squeak with each step. Of course, this is just an early prototype though, so Collins and Sawicki will probably address the squeakiness in future iterations of their exoskeleton. No word on when this gizmo will make it out of the lab, but keep your fingers crossed and you and I might be able to get exoskeletons of our own within the next couple years.