The light weight of the Cheetah legs and the extra contact time with the ground give Pistorius a clear advantage. But the prostheses 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 gain momentum.
The flexibility of the Cheetah legs is also a disadvantage, though how much is a source of disagreement. "It's like running on a mattress," Herr says. But Matthew Bundle, a biomechanist at Montana who worked with Herr and Weyand on the original study and sides with Weyand, counters, "Even if you factor in that force reduction of the prostheses [caused by the flexibility], 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. To which Bundle says, "The technology is enabling him to do something that nobody else can do. That's the definition of an advantage."
BOTH IN scientific papers and in the press, Herr and colleagues who side with Pistorius have argued that his leg-swing time is not actually 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." Herr and Pistorius have claimed that the swing time of U.S. sprinter Walter Dix was 0.274 of a second when Dix took bronze in the 100 meters in Beijing. But the video footage that led to that measurement was from NBC's television broadcast, whose frame rate is too slow for scientific research. When Dix was filmed with research-grade cameras at the 2007 and '08 U.S. championships, his leg-swing time in both instances was 0.32, consistent with that of other able-bodied sprinters.
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 the 1980s 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. It was nowhere near the typical time of the 6'1" Pistorius.
"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."
The study of runners with one prosthesis has shed light on double amputees. "Single amputees are limited by the speed of their biological limb," Weyand says. "They can't swing both legs at drastically different speeds."
Ralph Mann, a silver medalist in the 400-meter hurdles in 1972 and USA Track and Field's biomechanist for sprints and hurdles, has analyzed high-speed film of elite sprinters in every U.S. championship since 1982 and in 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 biomechanists, and all 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 there are 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.
In London the world will see a sprinter doing things that no one else has done, in terms of his leg-swing times and his perseverance. The scientific debate aside, Pistorius has become one of the Games' most uplifting figures. "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."