In those devastating early days after the operation, Hugh Herr had a recurring dream. He was running through the cornfields behind his parents’ house in rural Pennsylvania, going impossibly fast, the sun and the wind on his face, almost flying. The ineffable sensation of freedom remains vivid decades later. Then the 17-year-old would wake up to the stumps of his legs below his sheets and remember: Both his limbs had been amputated five inches below the knee. The doctors said he would never run again.
They were wrong. Almost every other day for four years now, Herr, 46, has been jogging the 1.7-mile wooded loop around Walden Pond in Massachusetts on specially designed prostheses. “I was out just yesterday,” he says. “It’s a beautiful run.”
For Herr science is intensely personal. Before his accident, he was a world-class rock climber—but a C and D high school student who attended vocational school at night and “didn’t know what 10 percent of 100 was.” Today he has a master’s degree in mechanical engineering from MIT and a Harvard Ph.D. in biophysics, and he is walking around on motorized bionic limbs that adjust 500 times a second for angle, stiffness, and torque. He designed them himself.
In early 2011 his company, iWalk—headquartered near the MIT campus in Cambridge, Massachusetts—will release the PowerFoot One, the world’s first robotic ankle-foot prosthesis, to the general public. With an electric motor, five internal microprocessors, and a quarter-size inertial measurement unit that tracks and adjusts its location in space, the PowerFoot One is a giant leap over existing prostheses. It reacts to changing terrain and different walking speeds much like a natural human foot, facilitating a normal gait and allowing its users to push off the ground with seven times as much power as is possible with the best of its predecessors, all while expending less energy.
Herr, who directs the Biomechatronics group at the MIT Media Lab, spent the last eight years studying and refining computer models of the human leg to develop the PowerFoot. Bit by bit he has overcome most of its limitations. Still, there remains one stark difference between his invention and the real human limb: Herr’s prosthesis does not connect to the central nervous system, so the wearer cannot move it just by thinking. At least not yet. Sharing an ambition that would have sounded like science fiction just a few years back, Herr and a handful of other prosthetics engineers are now working to create lifelike limbs that users can control with their minds.
