One of the biggest points of contention is limb-repositioning time. The average elite male sprinter moves his leg from back to front in 0.37 second. The five most recent world record holders in the 100-meter dash averaged 0.34 second. Pistorius swings his leg in 0.28 second, largely because his Cheetah's are lighter than a regular human leg. Pistorius's rivals are swinging a lower leg that weighs about 5.7 kilograms, whereas his lower leg only weighs 2.4 kilograms.
Kram and his researchers countered with a paper claiming to have measured Walter Dix, a 100-meter sprinter, swinging his leg faster than Pistorius. But they used television footage of Dix rather than the standard, high-speed research video generally used to make such measurements. "The differences here are relatively small, so doing it with TV video isn't going to cut it," says Jesus Dapena, a biomechanics researcher at Indiana University Bloomington who was not involved in the Rice study. High-speed footage for Dix from that same season does exist, Weyand says, and it shows the runner clearly repositioning his limbs at around the same rate as the average Olympic sprinter.
Swing time is important because it affects some central factors that determine how fast a person can run. Repositioning his legs faster means Pistorius can keep his foot on the ground longer than everyone else. It's a bit counterintuitive, but Weyand argues that a runner's speed is largely determined by how long he can keep his feet on the ground, rather than in the air. The longer a foot remains on the ground, the more time the person has to generate force that will propel him forward. More force generally means more speed.
Kram argues, however, that because the Cheetahs are made of carbon fiber, and are lighter, they can't transmit nearly as much force to the ground as a human leg can, creating less forward propulsion. So Pistorius has to push down harder than most people to get the same amount of force against the ground. Weyand counters that Pistorius simply doesn't need to push as hard to run just as fast.
Of course, other researchers have other theories about a possible advantage. Because Pistorius's Cheetah's don't tire, his lower leg stays springy throughout the entire race. For most 400-meter runners the second half of the race is where the real battle happens. Jim Matin, a researcher at the University of Utah, says that the lower leg is what weakens and slows runners. Martin thinks that if Pistorius ran in a competitive 600-meter race, Pistorius could set the world record.
Some of the arguing may be moot. The fact that Pistorius runs differently does not necessarily indicate an advantage, because even the most elite sprinters have their own running styles, says Jill McNitt-Gray, a researcher at the University of Southern California who wasn't involved in the Rice study. One sprinter might use his hips more than the next. Another may rely more on his arm thrust. Amputees develop ways to interact with their prosthetic that makes sense for them. "Your body is going to figure out how best to use [the prosthetic]," she says.
In many ways, studying Pistorius is difficult. There's only one of him, and only one good study that uses his specific physiology. There are no other Olympic-level double amputees, and single-leg amputees run totally differently. Imagine your right leg could swing 10 percent faster than your left; your left leg simply could not keep up. A person with one prosthetic and one intact leg can only go as fast as his slowest leg—generally the biological one.
To complicate matters further, science doesn't totally understand how running works. "We really don't know exactly the mechanics of running," Dapena says. They have a working idea, he says, but it's possible that the forces Weyand and Kram are debating aren't important. "It's a good logic," he says, "but it's not necessarily down pat that way."
Weyland will not say outright whether or not Pistorius should be allowed to run in the Olympics. Perhaps, he says, the sprinter represents something more important than the dispute over his light, springy legs. "I admire the heck out of him," he adds. "He's an excellent athlete who's worked like crazy and persevered and overcome."
For Kram, whether Pistorius should run comes down to power. "Oscar derives all of his power from what he had for breakfast." Athletes should be in a different race only when motors or alternate power sources are introduced, he says. "When you're tired you can't just twist the throttle. You have to find that desire or have that physiological ability to push. That's what makes the Olympics special." It's what makes Pistorius special, too, Kram says. He's pushed his whole life.