Össur Flex-Foot Cheetah

Oscar Pistorius and the Össur Flex-Foot Cheetah®

Do Flex-Foot Cheetahs give Oscar Pistorius a competitive advantage over able-bodied athletes?

Flex-Foot Cheetahs have been used by Paralympic athletes since 1996 and have been scientifically proven to not give a net advantage over able-bodied athletes.

Oscar Pistorius has been competing with the same Össur manufactured blades since 2004.

What was the CAS ruling?

The Court of Arbitration for Sport ruled in 2008 that Oscar Pistorius can legally compete in IAAF athletics races wearing ÖssurFlex-Foot Cheetahs.

Who was involved in the CAS ruling?

Two scientific teams presented their findings to the CAS. One team of scientists, led by Peter Brüggemann had been hired by the IAAF. The findings of an American team of scientists were presented by Hugh Herr and Rodger Kram.
Three judges presided: one from the IAAF, one chosen by Oscar Pistorius’ team and one who was neutral. It was a unanimous decision by all three judges to overturn the IAAF ban on Oscar Pistorius competing in events under their jurisdiction.

Is the Flex-Foot Cheetah in anyway bionic or motorised?No. Running-Specific Prostheses (RSPs) are passive-elastic springs that are designed to emulate biological legs. They store and return elastic energy, but cannot generate net positive power or absorb negative power.

Do Flex-Foot Cheetahs transmit more or less force than biological limbs?Force is one of the key components in generating running speed and extensive research has found that uni-lateral amputees cannot transmit as much force on the ground with their RSP as they can with their biological legs. Pistorius and other bilateral amputees are also unable to transmit as much force with either of their RSP-equipped legs.

As Oscar does not have any muscles and joints below the knee does it make him less susceptible to injury?Studies have shown that Paralympic athletes suffer more injuries (9.3 per 1,000 hours) during training compared to non-amputee sprinters (5.6-5.8 injuries per 1,000 hours).

The Paralympic figure is nearly the same as the rate of injuries that are sustained in collegiate American football which is obviously a contact sport.
Athletes with RSPs also have to cope with additional running injuries generated from the friction of their limbs and the prostheses which can limit their training time when compared to able-bodied athletes.
Are Oscar’s improved times over the course of his career down to his ability or the improved technology of his RSPs?The Flex-Foot Cheetah has changed very little since 1997 and Pistorius’ RSPs have remained the same since he underwent rigorous testing as part of the IAAF and the CAS assessments in 2007 and 2008.

Oscar has competed on the same RSPs for the past three years. Oscar’s improved times over the course of his career are due to his ability, his coaching and his hard work.

As Aimee Mullins, the American Paralympic pioneer and herself a double amputee, said in 2010: “If it was the legs that were making us superfast, I would have done a decade ago what he’s doing now, and so would others. Oscar’s not running with any different technology than what I ran with 14 years ago.”

Do the Flex-Foot Cheetahs give Oscar Pistorius any additional energy advantage?

RSPs have an elastic energy return of 92% whereas biological tendons offer between 93% and 95%. The Flex-Foot Cheetah blades emulate the elastic function of tendons, but they cannot do what a leg can do.

Brüggemann’s initial report suggested that the mechanical energy return of RSPs was greater than biological ankles but it did not take into account that in biological legs, energy is transferred from the quadriceps to the ankle during push-off.
Elastic energy is most important for long distance running whereas sprinting is about force production and minimisation of foot-ground contact time.
 

Does Oscar Pistorius use less metabolic energy than other runners?

Tests have proven that while his running economy is better than an average non-amputee runner, it is well within the range expected for elite and sub-elite non-amputee runners. The initial claim of 25% less energy consumption has been discredited and was never published in a scientific journal. Two subsequent studies on some 20 amputees have shown metabolic equivalence to non-amputees.

Is Oscar Pistorius’ stamina affected in the same way as an able-bodied athlete over the course of 400m?In the early part of his career, Pistorius’ split times showed that he did run the second half of his races faster than the first but as he has matured as sprinter his split times have reversed and are now similar to elite non-amputees. He now runs slower in the second half of his races. When he ran a personal best time of 45.07s in Lignano, Italy in July 2011, his split times were 21.9s/23.2s. 

Do Flex-Foot Cheetahs give their users a longer stride length than other athletes?IAAF spokesman Nick Davies has confirmed that when the initial video analysis was made of Pistorius’ running style in Rome in 2007 his stride length was the same as his nearest competitor. Further studies have demonstrated that Pistorius actually takes shorterstrides than his non-amputee competitors.

Does Pistorius have a shorter leg swing time than other athletes?It has been claimed because the Flex-Foot Cheetahs are lighter (approximately 2.8kg) than a human foot and calf, they facilitate an unnaturally shorter swing time which enables more strides to be taken. Some studies have compared video footage from the 100m Olympic finals in Beijing, showing bronze medallist Walter Dix ran with a leg swing-time of 0.274 seconds, faster than 0.297s generated by Pistorius in his 100m race win.
The 2008 Paralympic silver medallist Jim Bob Bizzell, who is a single amputee, had a shorter leg swing time for his heavier biological leg than his RPSs in the same race.

 

Are the Flex-Foot Cheetahs widely available to all Paralympic athletes who require them?

75%-80% of Paralympic amputee athletes wear Össur’s Flex-Foot Cheetahs, which have been in existence since 1996.

For further information interviews can be arranged with the following:

Hugh Herr, Associate Professor of Media Arts and Sciences and head of the Biomechatronics research group at the Massachusetts Institute of Technology Media Lab.

Rodger Kram, Associate Professor in the Integrative Physiology Department at the University of Colorado, Boulder.