Tapping the Energy in Every Little Action

Knee braces, backpacks, and other wearables can generate electricity from our motions.

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By adding an aluminum chassis (green) and generator (blue), scientists have customized a knee brace (red) so that it captures biomechanical energy with each stride.

Each time I walk past a health club and see, through the gleaming windows, dozens of people toiling away on treadmills and ellipticals, I silently cry a little. The exercise is good for them, certainly, but what a loss it is for the rest of us. After all, the calories they are so proudly burning had to be produced somehow, and the energy they expend won't be recovered. (At best, it will power the LCD display that tells them just how many calories are being wasted.)

Why can't our physical activity be harnessed to generate real, usable energy? Well, maybe it can be. A seemingly small but clever bunch of scientists has been approaching the challenge from various angles.

For instance, a new study in Science, described today in this New York Times story, demonstrates one such approach, which generates power from the human stride. "The device," according to the story, "looks a little like a simple knee brace with cyborg bling." It captures energy during the part of the stride when the knee is slowing the forward motion of the leg, and it even relieves the person using it of some of the physical effort required to perform that action.

"The idea," says Max Donelan, a locomotion researcher at Simon Fraser University in British Columbia and inventor of the motorized knee brace, is "to harvest energy in the background, without increasing effort, while you go about your everyday activities." He says the device could be used to power amputees' prosthetic limbs and diabetics' implanted insulin pumps or to recharge batteries that soldiers need in the field.

Other research is pointing the way toward shoes and backpacks that recover kinetic energy by similar principles. One of my favorites is a backpack, developed by Larry Rome of the University of Pennsylvania, that captures energy as the load of the pack shifts up and down. When someone wears a normal backpack, the oscillations of the load are part of what can cause discomfort in the hips and shoulders. In experiments reported in 2005 (subscription required), Rome found that wearers of his energy-generating pack experienced less discomfort and used less effort than they normally would—and produced up to 7.4 watts.

Rome has since taken that discovery a step further, designing a pack that uses elastic cords to minimize the load's vertical motion. That design, while not energy generating, could lessen the strain on the wearer and reduce the effort required to carry a load (subscription required).

All this is promising. Maybe someday our clothing and accessories will routinely draw energy from our every action. After all, those self-winding watches have been around for years.