It should come as no great surprise that walking with a prosthetic limb is difficult. According to a newly published paper on prosthesis, walking with a prosthetic foot requires 23 percent more energy than walking naturally. This is because a natural gait returns and recycles energy in an efficient way, but a prosthetic limb wastes energy with each step. Scientists Art Kuo and Steve Collins have created an artificial foot that significantly reduces the amount of energy spent used with each step.

Art Kuo is a professor of Mechanical Engineering and Biomedical Engineering at the University of Michigan. Collins has an associate research fellowship at the Delft University of Technology. Together, they have developed an artificial foot that more closely mimics a natural human walking gait.

Normal human walking wastes energy when each foot collides with the ground. However, in humans with functioning limbs, the ankle will exert force on the ground and make up for this loss of energy. Without an ankle to produce an external force, humans with prosthetic limbs waste energy with each step, and therefore must exert themselves more to walk.

In the Kuo-Collins artificial foot, the energy-recycling foot captures this wasted energy and puts it to use by mimicking the energy of pushing off the ankle. Using a mini-controller, the prosthetic foot captures the dissipated energy of each step and is able to give back the energy at the appropriate time. In a controlled experiment with non-amputee, dual-limbed, volunteers wearing either a sturdy gait-constricting boot or a prosthetic simulator, the research subjects only exerted fourteen percent more energy wearing the artificial foot than they exerted during normal walking. This means that the energy-saving foot reduces wasted energy by 9 percent, which may seem insignificant, but surely seems helpful to amputees.

This idea of reducing the energy loss associated with wearing a prosthetic foot is not new. However, older attempts at this type of energy return required internal motors and batteries. The artificial foot uses existing energy that would normally be wasted, and therefore only needs a small amount of electricity, about 1 Watt, which can be easily produced by a tiny battery.

The paper, published in the scientific journal PLoS ONE on February 17th, details the experiment, which was funded by the National Institutes of Health and the Dept. of Veterans Affairs. Researchers are currently testing the energy-recycling artificial foot at the Veterans Affairs Medical Center in Seattle, Washington. Both Kuo and Collins hope that this new prosthetic foot is a step in making walking with an artificial limb as natural as walking with flesh and bone.