Researchers from Simon Fraser University in Canada, and the University of Pittsburgh and the University of Michigan in the United States, have reported in the Feb. 8 issue of the journal Science that they built a new energy-capturing knee brace.

The device generates enough energy to power a mobile phone for 30 minutes from one minute of walking. The brace operates similar to the regenerative braking in electric and hybrid cars, a principle used for decades in trolleys. Somewhat similarly, the amazing device captures the energy lost when a human brakes the knee after swinging the leg forward to take a step.

"There is power to be harvested from various places in the body, and you can use that to generate electricity. The knee is probably the best place," said Arthur Kuo, an associate professor of mechanical engineering at the University of Michigan and an author of the paper, as quoted by physorg.com. "During walking, you dissipate energy in various places, when your foot hits the ground, for example. You have to make up for this by performing work with your muscles.

The main application for the technology will be prosthetics. There are advanced prosthetics in development but all require power for electronics and electromechanics in it. The 3.5 lbs device produced an average of 5 watts of electricity from a slow walk. A more energetic movement can generate up to 13 watts, but that kind of power comes with a significant effort from the bearer of the contraption.

"All of the new developments in prosthetics require large power budgets," Dr Douglas Weber of the University of Pittsburgh, and one of the authors of the paper, told BBC News. "You need power to run your neural interface; you need it to run your powered joint, and so on. Getting that power is going to be really important."

Eventually the technology will be incorporated in powered prosthetic limbs. The researchers allege that the bearers didn't notice whether it is switched on or off when walking on a treadmill.