Frustrated by your iPod batteries dying while you’re on the treadmill? Keep an eye out for a new knee brace designed to harvest energy from a walker’s stride. From only one minute of movement, the device outlined in the journal Science can generate enough energy to power a cell phone for half an hour. A lightweight version of the brace could be available within 18 months and “promises to have significant medical, military, and consumer applications,” says lead researcher Max Donelan. “It allows a soldier to get back home safely. It benefits stroke victims, amputees, and others who rely on power-assisted medical devices for mobility.” And, of course, could assuage your iPod woes, if you shake a leg.