for National Geographic News
Inspector Gadget, take note: Researchers have created a knee brace that converts the energy from a walker's stride into electricity.
Results from the device show that if the clumsy cartoon character wore a brace on each leg as he stumbled after his nemesis Dr. Claw, he'd easily generate five watts of electricity.
That's enough juice to power ten cell phones at once—or in the inspector's case, perhaps enough to keep his telescoping appendages functioning for an entire TV episode.
More practical and immediate applications are for "people whose lives depend on portable power," said Max Donelan, a professor of kinesiology at Simon Fraser University in Burnaby, Canada.
For example, he said, the knee brace could help power electronic prosthetic limbs worn by amputees or help soldiers charge batteries for essential battlefield gadgets like night vision goggles.
(Related photo: "Bionic Hand Unveiled in Britain" [July 19, 2007].)
Donelan and his colleagues describe the high-tech knee brace in tomorrow's issue of the journal Science.
Donelan said the contraption is similar, in theory, to a hybrid-electric car, in which energy normally dissipated as heat during braking drives an electric generator instead.
"We use essentially that same principle and apply it to walking," he said.
The knee-brace generator kicks on at the end phase of a stride, when the hamstrings—the muscles at the back of the thigh—normally activate to help brake the leg.
(Watch a video about how the human body works.)
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