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Best Foot Forward

by Lindsey McCormack
March/April 2008 , Page 29

Hugh Herr's PowerFoot One

We study how the human leg works, and that motivates what we build."

When he was 17, Hugh Herr became stranded on Mount Washington during a blizzard, leading to a double amputation of his legs below the knee. What frostbite took away, the avid mountaineer made it his mission to reclaim. In 1982, he fashioned a prosthesis that allowed him to continue rock climbing. Later, as a Ph.D student in biophysics, he began designing a series of mechanical limbs. His latest invention, PowerFoot One, will debut this summer as the most advanced robotic ankle on the market.

Herr, who holds professorships at both MIT and Harvard, works in two labs—he calls them “robotic stations”—that are strewn with prototypes in various stages of completion. “We study how the human leg works, and that motivates what we build,” Herr says.

In an intact leg, the tendons act like energy-absorbing springs, allowing the muscles to operate with maximum efficiency. Traditional prostheses try to mimic that effect through a passive spring that pushes back at the end of each step. But the lack of muscle power requires the walker to expend extra energy, often leading to chronic hip and back pain. Herr’s breakthrough idea was to partly motorize the ankle, replicating the tendon and muscle action that makes walking easy for most of us. At the unveiling of the prototype last July at the VA Medical Center in Providence, R.I., Herr described the sensation as similar to strolling on a moving sidewalk.

Hugh Herr works on a prototype

The emergence of sophisticated prosthetics like the PowerFoot is, in part, a sad sign of the times. As more soldiers return from Iraq and Afghanistan with damaged or missing limbs, the Department of Veteran’s Affairs has boosted funding for research like Herr’s. Meanwhile, by spinning off his federally funded research into a start-up called iWalk, Herr hopes to help other amputee groups, such as diabetics. His next project: a robotic limb for people with full-leg amputations.
Robotic Foot

For more information on PowerFoot One, visit [www.iwalkpro.com]