The advantage comes from a significant reduction of leg mass (and especially, I should add, a displacement of the legs center of mass to a point much closer to the body) which allows for much faster swing times. It’s not difficult to imagine the effect of something like this in reverse. Hold in each hand an object such that the weight of your arm is significantly increased by a comparable amount as the difference between a blade and a normal leg. Now swing your arms as fast as you can, and feel how much harder it is to swing them. Or tape some considerable weight to the middle of your calves, or to your shoes, and feel how much this slows down you leg swing.
From the IE article quoted previously:
In 2000, Weyand and a team of researchers at Harvard published a study showing that humans, from couch potatoes to pro sprinters, have essentially the same leg-swing times when they achieve their maximum speed. Says Weyand, "The line we use around the lab is, From Usain Bolt to Grandma, they reposition their limbs in virtually the same amount of time."
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."
[…]
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."
[…]
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.
Amazingly, the defense manages to keep things fuzzy by insisting that the disadvantages might perhaps offset the advantages, we just don’t know, it can’t be measured, and therefore he should be allowed. I find this astonishing. Let’s say there is a hunting competition using bow and arrow. But a certain guy (with bad eyesight and only one arm), is allowed to join the competition using a gun. When people suggest this doesn’t make sense, the defenders point out that his lack of an arm and bad eyesight offset the advantage of the gun. It just makes no sense.
