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Faster, better, stronger?

Some high-tech prosthetics look as if they'd give athletes an advantage, but perception might not jibe with reality.

July 23, 2007|Jeannine Stein | Times Staff Writer

With sleek, curved prosthetic legs that appear straight out of a sci-fi movie, sprinter Oscar Pistorius has been blazing across running tracks, leaving controversy in his wake.

At issue is whether those carbon graphite appendages give the 20-year-old South African bilateral amputee an advantage over able-bodied runners, an issue that's yet to be determined as he makes a bid for the 2008 Olympics in Beijing. No, say prosthetic manufacturers, other amputee athletes and researchers. Maybe, says the International Assn. of Athletic Federations, the governing body of world track and field, which continues to study the matter before making a ruling.

Although national Olympic committees ultimately select the competitors, technical rules in track and field are enforced by the IAAF. And one of its rules forbids "technical aids that give the competitor an advantage over someone not using them."

As prosthetics improve and training techniques advance, such cases are likely to become more common. Even as prosthetic designers try to devise limbs that would be an improvement over biological limbs, many of today's amputees are determined to be as fit and competitive as possible. In doing so, they're going up against the fittest of able-bodied athletes, regardless of the odds.

A little more than a week ago, Pistorius placed seventh at a race in England, running the 400 meters before being disqualified for going outside his lane. But he had already garnered attention for holding world records in the Paralympics. Although he's not the first disabled athlete to compete against able-bodied athletes, he is the first bilateral amputee who may make the crossover.

The prevailing sentiment among those who work with amputees is this: "I think he has a distinct disadvantage," says Hugh Herr, associate professor of media arts and sciences at MIT. A double amputee himself, Herr is director of the school's Biomechatronics Group. "The prosthetic he's using is completely passive -- it's just a spring." A spring, he adds, that can't possibly compare with the force with which the human leg can propel a foot off the ground. "That comes from the muscles, and he has no muscles," Herr says. "He's just really fast."

Amputee athletes must compensate for what they don't have -- muscles, tendons, ligaments, joints, bones -- things that even a state-of-the-art passive prosthetic can't re-create at this stage, researchers say. That compensation varies depending on whether a person is a single or double amputee, how much of the leg is left, and individual biomechanics.

Pistorius was born without fibula, or calf bone, in either leg, and at 11 months his legs were amputated below the knee. He began competing in track at 17 and quickly began racking up medals in Paralympic events. He began racing against able-bodied athletes in 2005, coming in sixth in the South African Open Championships.

He runs on the Cheetah foot manufactured by Ossur, an Icelandic prosthetic and brace manufacturer. Its J-shaped design, based on an actual cheetah foot, has been available since 2001.

But as much as amputee runners favor the artificial running foot, it can't compare to the biological version, say scientists and researchers. In a 1987 study published in Archives of Physical Medical Rehabilitation, researchers evaluated the Flex-Foot, made by Ossur and similar to the Cheetah, against a human foot. Landing on a human foot in a running stride gave a 241% spring efficiency, or energy return, because of the contraction of the calf muscles. In comparison, the Flex-Foot had an 82% spring efficiency.

"It's the muscle that will actually help propel you," specifically the calf muscle, says Robert Gailey, associate professor in the University of Miami's department of physical therapy, and director of the Functional Outcomes Rehabilitation and Evaluation Laboratory at the Miami VA Medical Center.

The bounce that Pistorius and other amputee athletes have with the Cheetah is created not by actual springs but by the bending of the carbon graphite -- the prostheses don't accelerate the runner like Inspector Gadget. An athlete still has to power his own legs, a force that in Pistorius' case comes from his hips.

Also, Pistorius' legs pound into his sockets with every stride, and though suction helps keep them in place, Gailey points out, he still has to create stability as he makes contact with the ground. Stability issues and centrifugal forces may make it more difficult for him to maneuver around a curved track. Whereas able-bodied runners are fast out of the starting blocks, a lack of ankles and Achilles tendons give Pistorius a far slower start.

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