Prosthetic limb researcher Hugh Herr
shows off his wares in his biomechanics lab at MIT.

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.

“I think the prosthetics are more attractive than human legs,” Herr says

There are nearly 2 million amputees in the United States alone who could benefit from these breakthroughs. Most immediately, Herr’s inventions could soon enable the million-plus people who are missing lower limbs to do things they can now only dream of: Standing on tiptoes to pull a jar out from the back of a cabinet. Flexing their feet to put on shoes. Dancing.

That Herr is so close to achieving this dream is remarkable in itself. What is even more extraordinary is the path he trod to get there.

The first flakes had begun to fall when Herr and his pal Jeff Batzer headed into the wilds surrounding New Hampshire’s Mount Washington, the Northeast’s highest peak, to ice climb and hike in January 1982. By the time the teenagers turned to head back, just a few feet from the summit, the wind was gusting at up to 94 miles an hour, visibility was less than 10 feet, and the temperature had fallen below zero. The two became disoriented and headed in the wrong direction.

It was three days before a woman in snowshoes stumbled upon the boys’ tracks and found them huddled and frozen, hours from death. By then, an avalanche had claimed the life of a searcher, and both Herr and Batzer had severe frostbite. Doctors amputated four of Batzer’s fingers, a thumb, his left foot, and all the toes on his right. Herr wasn’t as lucky.