Faster, better, stronger?
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.
But the IAAF still has some questions to answer before it determines if Pistorius can compete (no date is set for that ruling). According to spokesman Nick Davies, the organization would like to measure his VO2 max (the maximum amount of oxygen, in milliliters, that the body uses in one minute, per kilogram of body weight) and measure the mechanical efficiency of Pistorius’ running style using force plates, 3-D kinematics and other techniques. All results would be compared with those of able-bodied runners. His running has already been filmed so that his stride length and speed over various parts of the track can be analyzed.
Part of what may frustrate IAAF officials is the lack of research done on amputee athletes. That, says Gailey and others say, is due to the small pool of elite athletes available for study, and the fact that research money is used primarily to develop prosthetics to help people walk better.
That’s changing. Today, bionics and robotics are two main areas of prosthetic research. Herr has developed the first powered, computer-controlled robotic ankle that allows a faster and more natural gait. It will be available to consumers in about a year, he says. He also developed Ossur’s Rheo Knee, which contains a microprocessor that adapts to changes in speed, load and terrain.
At Northwestern University’s Prosthetic Research Laboratory and Rehabilitation Engineering Research Program, director Steven Gard says his lab is working on a foot and ankle mechanism that will better adapt to changing terrains and walking speeds. Erik Schaffer, a certified prosthetist and owner of A Step Ahead, a prosthetics and orthotics company in New York, says he’s inspired by the athletes he works with to develop new and better prosthetics “as athletes push the boundaries.” But prostheses are still not as strong and powerful as biological limbs. Nor are they linked to the nervous system, Herr says, which would allow a person to “think and have the limb respond, so it behaves automatically in an appropriate way.”
Yet he and others working on improving prosthetics are sure that one day the devices will be more integrated with the human body. And here’s where the debate about amputee versus able-bodied athletes gets even thornier: “Our goal is to design a running prosthetic that would actually give an amputee an advantage” over an able-bodied person, Herr says.
The artificial leg would actually save energy as it propels someone along. So as Pistorius narrows the gap between disabled and able-bodied athletes, technology could eventually split them apart again.
“If there are no constraints placed on what technology can be used,” Herr says, “at some point there will be an advantage the amputee athlete has. In the future, Paralympic running times will be faster than the Olympics.”