While tried-and-true for thousands of years, climbing stairs is a chore that's inspired some creative alternatives, such as the Vertical Walking system or the Vycle. Now a team from Georgia Tech and Emory University has developed energy-recycling stairs that take some of the pressure off the knees and ankles, by storing energy from people descending then giving it back as they climb up.

Most of us might not think about the mechanics of our movements when going up or down stairs, but it seems reasonable to assume that ascending would waste more energy. But that's not the case, according to the Georgia-Emory team, who describe the downward journey as like tapping the brakes on a car while revving the engine.

"Unlike normal walking where each heel-strike dissipates energy that can be potentially restored, stair ascent is actually very energy efficient; most energy you put in goes into potential energy to lift you up," says Karen Liu, co-author of the study. "But then I realized that going downstairs is quite wasteful. You dissipate energy to stop yourself from falling, and I thought it would be great if we could store the energy wasted during descent and return it to the user during ascent."

To recycle that energy, the team created stairs that are spring-loaded and fitted with pressure sensors. When someone walks down the stairs, each step compresses, sliding down until it's level with the next step before locking into place. That captures the energy that's normally wasted, and stores it until someone goes to walk up the stairs. Then it happens in reverse: a pressure sensor on one step triggers the release of the step below it, which then rises until it's level with the next one, reducing the strain on the trailing ankle.

The team says the system reduces dissipated energy by 26 percent on the way down, and makes it 37 percent easier on the knee on the way back up. Those figures might not mean much to people with full mobility, but it could make all the difference for pregnant women, the elderly, or those recovering from surgery.

The system can be fitted over an existing staircase, either permanently or temporarily. The latter is important because, in the case of pregnancy or injury, people might only need assistance for a short while, so building in a long-term fixture is unnecessary.

"Current solutions for people who need help aren't very affordable," says Liu. "Elevators and stair-lifts are often impractical to install at home. Low-cost, easily installed assistive stairs could be a way to allow people to retain their ability to use stairs and not move out of their homes."

The research was published in the journal Public Library of Science PLOS ONE, and the team demonstrates the spring-loaded stairs in the video below.

Source: Georgia Tech

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