A stroll around the park may soon be enough to charge the raft of batteries needed in today's power-hungry gadgets.
US and Canadian scientists have built a novel device that effortlessly harvests energy from human movements.
The adapted knee brace, outlined in the journal Science, can generate enough energy to power a mobile phone for 30 minutes from one minute of walking.
The first people to benefit could be amputees who are being fitted with increasingly sophisticated prosthetics.
"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.
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