18 February 2010

Artificial foot reuses energy lost in walking

Cosmos Online
Researchers have created a prosthetic foot that recycles the energy normally lost during walking, a development that could make it easier for amputees to walk.

Credit: iStockphoto

BOSTON: Researchers have created a prosthetic foot that recycles the energy normally lost during walking, a development that could make it easier for amputees to walk.

“For amputees, what they experience when they’re trying to walk normally is what I would experience if I were carrying an extra 30 pounds [13.5 kg],” said Art Kuo, a study coauthor and a mechanical engineer at the University of Michigan.

The new prosthetic foot reduces this difficulty by putting the energy that is normally wasted during walking to use. The device, which is outlined in the journal PLoS ONE, therefore lowers walking effort for the user.

Human gait wastes energy

A typical prosthesis cannot reproduce the force an ankle exerts to push off the ground, meaning amputees must expend more energy to walk.

To quantify exactly how much energy, the researchers asked non-amputees to walk normally and then with a prosthetic simulator. They found walking with the prosthesis required 23% more energy.

Plus, the human gait itself wastes energy. “Normally during walking, your whole leg acts like a damper, removing energy like the shocks of an automobile at the beginning of each step,” said Steve Collins, a coauthor and biomechanical engineer at the Delft University of Technology in the Netherlands.

Supplementing the ankle

The researchers worked to put that wasted energy to use in powering the ankle push-off.

Their artificial foot captures the energy and releases it in exactly the right way to supplement the ankle push-off. As a result, walking is made much easier.

When the non-amputee testers walked with the new device, they only spent 14% more energy than they did walking naturally, meaning the prosthetic energy penalty is almost cut in half.

Other prosthetic devices also work to boost ankle push-off, but they require motors and large batteries. Their bulkiness results in limited mobility.

The new prototype, by taking advantage of the wasted energy, uses less than one Watt of electricity and a small, portable battery. It could therefore be a less restrictive option than conventional devices.

“We have designed this foot with the intent to turn it into a prosthesis for amputees,” Collins said, adding that it could be widely available within two to five years. The design is currently being tested for amputee patients at the Veterans Affairs Medical Center in Seattle, Washington.

Thomas Sugar, an engineer at Arizona State University, said that the idea of recycling wasted energy shows promise for better prosthetics.

“Developing new prosthetic ankles that recycle or regenerate energy is an exciting new field in advanced prosthetics,” he said. “It will allow users to walk more comfortably and use less energy while walking.”

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