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A new study shows that prostheses hinder running performance
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Oscar Pistorius, "the fastest man on no legs" runs on his Cheetah
Flex-foot prosthetics, which scientists have found are not as fast as
biological legs. Photo by Elvar Pálsson from Wikimedia Commons
An outcry was raised in 2008 when Oscar Pistorius, a double-amputee sprinter from South Africa tried to qualify for the (able-bodied) Olympics. Some critics screamed foul, claiming that because Pistorius had no leg muscles, his cardiovascular system had to supply oxygen to less muscle tissue, providing a performance advantage. The IAAF (track and field's international governing body) subsequently amended their rule book to ban "any technical device that incorporates springs, wheels or any other element that provides a user with an advantage over another athlete not using such a device." Pistorius and the world were dumbfounded. A man with no legs had an advantage in the 400m sprint?
Pistorius argued that, since sprinting is an anaerobic event, aerobic capacity didn't enter into the equation. Aerobic capacity might be a factor for a legless marathoner, but not a sprinter. A team of biomechanical experts underwent a hasty study and confirmed Pistorius' argument. Four months later, the Court of Arbitration of Sport overturned the IAAF's ruling. Pistorius was allowed to compete in the Olympic trials, but missed the qualifying time by three quarters of a second.
In 2005 Sarah Reinertsen became the first female
above-the-knee amputee to finish the Ironman.
Reinertsen runs on a prosthetic like the one studied.
Photo: Business Wire
No longer under a deadline, seven biomechanical experts who had testified in Pistorius' favor in 2008 began a study of six elite unilateral (one-legged) amputees who use a running prosthesis similar to the Cheetah Flex-foot used by Pistorius. They studied the stride timing and forces exerted on the ground with both the biological leg and the prosthesis at speeds from jogging to all-out sprinting. Their findings, which were published on Wednesday in the Biology Letters of the Royal Society of London found that rather than providing an advantage, the prosthetics actually provide less ground reaction forces. Since the force with which your leg hits the ground is largely responsible for speed, running on prosthetic limbs actually hinders running performance rather than enhancing it. "These new data support our previous findings that passive running-specific prostheses are not able to provide the ground forces realized by biological legs, and that we are not yet at a point in time when lower-limb prostheses outperform biological limbs," Alena Grabowski, who is a member of the Biomechanitronics Group from MIT's Media Lab told the Business Wire.
"Unilateral amputee sprinters simply cannot strike the ground as hard and fast with their prosthetic leg as compared to their biological leg, a clear disadvantage for achieving top sprinting speeds," explained Hugh Herr, who lead the study. The researchers admit, however, that they have only just begun to scratch the surface of the issue. "[B]ecause the biomechanical and physiological comparisons of amputee runners using prostheses to non-amputee runners are so complex, we will continue conducting additional research to better understand all the factors involved," said Grabowski.
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