PUBLISHED 02/29/2008
In January, an independent study found that the prosthetic limbs used by Oscar Pistorius, a double below-the-knee amputee, give him an unfair advantage over runners with two whole legs, thus violating an International Amateur Athletics Federation rule that prohibits the use of technical aids. As a result, the IAAF banned the South African 400-meter specialist from competing in IAAF-sanctioned events--including the 2008 Olympic Summer Games in Beijing, China.
If you're having a hard time wrapping your head around the idea that running on artificial legs can give you an edge, you're not alone. Pistorius and his supporters have appealed the ruling.
They'll face an uphill battle. After a battery of tests, Peter Br?ggemann, one of the world's leading experts in running biomechanics, concluded that Pistorius's prostheses--called Cheetahs--enable him to use significantly less energy than able-bodied athletes when running at the same speed. "The difference is substantial; much greater than you'd ever see naturally among athletes," says Ross Tucker, Ph.D., an exercise physiologist at the University of Cape Town, South Africa.
The full study has not been released, but Tucker has interpreted the results for Runner's World based on the following key findings reported by the IAAF.
Less Energy Loss
When the foot hits the ground running, it moves through a landing, a stance (pause), and a push-off phase. Energy is lost during the stance. Br?ggemann found that the Cheetahs lost 9.3 percent versus the 41.4 percent energy loss experienced by able-bodied sprinters. That translates into more power per stride.
Less Vertical Motion
Faster runners tend to produce less vertical oscillation than slower ones, meaning they don't bounce as much and therefore waste less energy. The Cheetahs produce significantly less vertical force than the human foot. So the energy return produced by the blades pushes Pistorius in the right direction--forward, not up.
Less Fatigue
Tucker believes the small loss of propulsion Pistorius experiences by not having lower-leg muscles is more than made up for by the fact that the Cheetahs have no chance of fatiguing. Plus, they weigh less. "The mass of each prothesis is about 2.2 pounds, which is 13 to 17 pounds less than a human lower leg," says Tucker.
Equal Speed, Less Energy
Pistorius can run the same speed as able-bodied sprinters using 25 percent less oxygen, due to the blade's energy return. "That's a shocking number," says Tucker, who expected a figure closer to five percent. This gives Pistorius an edge in the second half of a 400-meter race--most sprinters slow down; he often speeds up.
Superior Energy Return
When you run, the body sends energy into the ground and receives some back, which helps propel you forward. Because the Cheetah's carbon-fiber blades are so stiff, they produce three times more energy return than a human ankle. "There's evidence that a stiffer tendon returns more energy," says Tucker, "and the Cheetah is a lot stiffer than any human leg."
