Fair or foul? Experts split over whether Pistorius has advantage
LONDON-- Before he changed into his racing legs, South African double-amputee sprinter Oscar Pistorius made sure to greet each and every photographer who showed up to shoot his training session last Sunday at St. Mary's University College in Twickenham, far in the south of London. At the very same time that one of his PR reps was insisting that he wouldn't be talking at all today, Pistorius was busily talking to everyone he could see. He greeted every onlooker with a handshake, going back when he missed one person. "I think I forgot to greet you," he said softly, and extended his hand. The display prompted a British photographer to remark: "I've never come across that. He doesn't need any PR, does he?" And it's all the more remarkable considering that such manners flowed from a man who is an A-list celebrity in South Africa. Pistorius has owned white tigers and racehorses, and the gossip pages recently reported that he's dating a Russian supermodel. (Two days ago, a zealous fan showed him a
That Pistorius is charismatic is beyond questioning. Nor is there any doubt of the magnitude of the inspiration he engenders. Pistorius's Twitter picture is a shot of him -- in his crescent, carbon-fiber Cheetah Flex-Feet -- leaning down and jogging beside a little blonde girl whose own Cheetah legs are protruding, adorably, from beneath her tiny yellow sun dress. Or how about this scene, which sounds like the Paralympic
When the "Blade Runner" steps onto the track Saturday, it will be as South Africa's top quarter-miler of 2012 and the first double-amputee (and first male Paralympian of any sort) to compete in the Olympics. And even though Pistorius -- who had both lower legs amputated before he was a year old -- is a veritable fount of inspiration, questions about his carbon fiber racing legs have followed him to London. Just before the Games began, Michael Johnson -- Pistorius's friend and the 400-meter world record holder -- said that Pistorius should not be competing against able-bodied runners.
"My position is that because we don't know for sure whether he gets an advantage from the prosthetics that he wears, it is unfair to the able-bodied competitors," Johnson said. "That is hard for a lot of people to take and to understand when you are talking about an athlete and an individual who has a disability."
The questions started almost as soon as Pistorius began racing, even before he earned the moniker, "fastest man on no legs." In the summer of 2003, Pistorius injured his knee playing rugby for Pretoria Boys High School and took up track as a form of rehabilitation. The following summer, at age 17, and just eight months into his track training, Pistorius donned Cheetahs for the 2004 Athens Paralympics. He won gold in the 200 -- an event that combines single- and double-leg amputees -- shattering the world record. According to a former U.S. Paralympics official, single-leg amputees, feeling that they were at a disadvantage against Pistorius, began to complain.
In 2007, with the blessing of the IAAF -- the governing body for track and field -- Pistorius competed in the 400 in a Golden League meet in Rome, against professional sprinters with intact limbs. It was not only a history-making event, but also an athletic success. Pistorius came from dead last in the final 70 meters to finish second in his heat. But the way he ran the race only intensified the questions. Nearly all elite quarter-milers burst out of the blocks and spend the race trying to slow down as slowly as possible, but slow down they do. Pistorius "negative-split" the race in Rome, meaning that he ran the second 200 faster than the first, an unheard of strategy for elite quarter-milers. (Pistorius, though, no longer negative-splits his races.)
Among track aficionados, certain statistical comparisons have raised eyebrows: Pistorius's 100- and 200-meter bests are similar to those of U.S. sprinter Allyson Felix, but he is 4.5 seconds faster than her in the 400. As Pistorius progressed to where he could compete for a spot on South Africa's national team, another South African 400 runner who was also fighting for a spot, Sibusiso Sishi, gave his opinion: "I don't mind racing [Pistorius], but I'm still a bit skeptical about his legs because they are man-made. They are carbon fiber, which means they are nice and light. I would just like him to do the tests so at least we know where we stand."
With Pistorius knocking on the Olympic-qualifying door, in late 2007, the IAAF asked Peter Brüggemann of the German Sport University to test Pistorius and his blades. Brüggemann subsequently reported to the IAAF that the Cheetah blades allow Pistorius to expend less energy than other runners, and, as result, Pistorius was banned from able-bodied competition.
Pistorius appealed the ban to the Court of Arbitration for Sport (CAS). He went for more testing, this time in a lab at Rice University run by physiologist Peter Weyand. The data from that testing found that Pistorius fatigued at a normal rate. Not to mention that energy efficiency has about as much to do with sprint performance as fuel efficiency does with drag-racing performance. University of Colorado physiologist Rodger Kram and Hugh Herr, a professor at MIT and world-renowned designer of prosthetics -- both members of the scientific team that did the second analysis of Pistorius -- presented the data to the CAS.
Herr, whose own designs have
In May of 2008, based on Kram and Herr's testimony and the data the team collected in Weyand's lab, Pistorius was reinstated. The CAS ruling explicitly noted that though the prostheses give no energetic advantage relevant to sprinting, future scientific findings could still show that the Cheetah Flex-Feet give Pistorius a mechanical advantage. Eighteen months later, Weyand and Matthew Bundle, a biomechanist at Montana and one of the other scientists who did the testing that got Pistorius reinstated, came out and said that the Cheetahs do just that.
"It was dead obvious as soon as [Bundle and I] saw the data that Oscar has an advantage," says Peter Weyand, who now directs the SMU Locomotor Performance Laboratory. "We haven't wavered from that interpretation since."
Because the CAS hearing examined specifically -- and only -- the IAAF's previous claims regarding Pistorius, it was not until the following year, when the scientific team published its full findings in the
All sprinters run essentially the same way. Sure, Usain Bolt is 6-foot-5 and flies down the track smirking, while Tyson Gay is 5-11 and runs with his eyelids peeled back. But biomechanically they are doing the same thing. At top speed, each piston pump of a sprinter's leg slams a foot down on the ground for less than a 10th of a second. In that instant -- much briefer than the blink of any eye -- the sprinter applies enough force to lift his body back into the air for slightly more than a 10th of a second. That's how long he needs to bring the other leg forward and pound the track once again. And it's not just top male sprinters such as Bolt and Gay who have this in common. It is also female sprint stars such as Allyson Felix and Carmelita Jeter, not to mention all those other sprinters, male and female, who have no hope of getting past the first-round heats in London. (The high-speed video below shows the contact time and force application of an Olympic sprinter.)
A primary difference between the best sprinters and their slower competitors lies in how much force each one applies in that fraction of a second when their foot is on the ground. (A normal person running at top speed applies an average force of about twice his body weight over the contact time; Gay applies closer to 2.5 times his body weight.) The rate at which a sprinter swings his legs through the air might also seem important in differentiating him from his rivals, but all able-bodied sprinters swing their legs at nearly the same rate: about a third of a second between strides.
"All the fast guys do it the same way," Weyand says. "If you know their top speed and their leg length, without knowing anything else you can predict the time they'll spend on the ground and the time in the air and the ground forces."
In 2000, Weyand and a team of researchers at Harvard
But Pistorius's leg-swing times, when measured on a high-speed treadmill, were off the human charts. At top speed, he swings his legs between strides in 0.284 of a second, which is 20 percent faster than intact-limbed sprinters with the same top speed. "His limbs are 20 percent lighter," Weyand says, "and he swings them 20 percent faster."
This is important because it allows Pistorius to circumvent a main requirement of top level sprinting: putting high forces into the ground quickly. Because Pistorius can make up time with his rapid leg swing, he can leave his foot in contact with the ground longer than other sprinters. To attain the same speed, Pistorius applies lower forces -- about 20 percent lower --
The light weight of the Cheetah legs and the extra contact time with the ground give Pistorius a clear advantage. But the prostheses also have drawbacks. Pistorius is slower at the start than his competitors are. Without ankles, he has to stand straight up out of the blocks and start bouncing to build momentum. And the flexibility of the Cheetah legs has a disadvantage.
"Even if you factor in the force reduction of the prostheses," Bundle says, "Pistorius is still seven seconds faster over 400 meters than he would be if his limbs functioned as intact biological legs do." (That is, if his swing times were typical of able-bodied runners.)
Herr, defending Pistorius, contends that the South African's rapid swing times are merely compensation for the force deficit caused by the Cheetahs and that researchers may never be able to quantify all the advantages and disadvantages of running on carbon-fiber blades. "It's going to take years and years," he says, "and it may not be knowable." To which Bundle says, "The technology is enabling him to do something that nobody else can do. That's the very definition of an advantage."
Both in scientific papers and in the press, Herr and colleagues who side with him have argued that Pistorius's leg-swing time is not truly off the biological charts. "Regarding swing times," Herr says, "one would get really suspicious that there is augmentation if ... no one with a biological body has ever achieved that metric. But it's not the case."
SI reviewed more than 100 leg-swing times of professional sprinters taken with research-quality cameras, as well as peer-reviewed scientific journal reports on sprinters' swing times from Ben Johnson and Carl Lewis to the present. The fastest swing time reported was 0.30 of a second, by Trindon Holliday, the 5-5 Houston Texans wide receiver, when he was competing in the 100 at U.S. nationals in 2007. But the 6-1 Pistorius' swing time was still far faster.
"Thousands of amputees have used these springs and haven't even come close to his times," Herr says of Pistorius. But, says Craig Spence, a spokesman for the International Paralympic Committee, "there aren't too many double-leg amputees who compete [in sprints]. There are two or three, so therefore they're combined with the single-leg amputees." Says Weyand, "single-leg amputees are limited by the speed of their biological limb. They can't swing both legs at drastically different speeds."
Ralph Mann, a silver medalist in the 400 hurdles in 1972 and USA Track and Field's director of sports science for sprints and hurdles, has likely analyzed high-speed film of more sprinters than any person in the world -- every U.S. championship since 1982, several world championships and five Olympic Games. When he saw the Pistorius data, he says, "I came to the conclusion that he's not using normal human ground time and air time. Air times are basically the same for every sprinter on the planet, whether high school, collegiate or pro."
SI spoke with eight independent physiologists and biomechanics experts who had no involvement with testing Pistorius, and all eight agreed that Pistorius has abnormally low leg-swing times, stemming from the lightness of his prostheses. Four felt that Pistorius has an advantage over his competitors, while four said that the low swing time is an advantage but that there may be other potential disadvantages to the prostheses that must be studied in more detail before they could say if Pistorius should be allowed to race against intact runners. "It's innocent until proven guilty," Herr says.
In London, the world is seeing a sprinter doing things that no one has done before, in terms of both his leg-swing times and his personal perseverance.
"What Oscar has done represents for a lot of people an unwillingness to accept expectations others might impose on you," Weyand says. "And that part is inspiring and makes you feel great about human nature."
On that, all can agree.