Call it the ultimate power walk.
Researchers have developed a device that generates electrical power from the swing of a walking person's knee.
With each stride, the leg accelerates and then decelerates, using energy both for moving and braking. Max Donelan and colleagues reasoned that a device that helps the leg decelerate could generate power without requiring much additional energy from the person. It's similar to the way some hybrid-electric cars produce electricity from braking.
With the device, a minute of walking can power a cellphone for 10 minutes, said Donelan, of Simon Fraser University in Canada. The device could also potentially power a portable GPS locater, a motorized prosthetic joint or implanted drug pumps.
Donelan and colleagues at the University of Pittsburgh and the University of Michigan reported development of the device in Friday's edition of the journal Science.
The first practical use for the generator is likely to be in producing power for artificial limbs, said Donelan, who with his coauthors has founded a company to develop the device commercially.
The generator weighs about 3.5 pounds, so users do burn energy carrying it on their knee, but they don't notice whether it is switched on or off when walking on a treadmill, he said.