Athletes sprinting with left leg prostheses could miss out on golds at Paralympics

The debate about Paralympic athletes competing against able-bodied athletes has raged since before Oscar Pistorius took the track on his Flex-Foot Cheetah prosthetic leg on 4 August 2012 at the London Olympics. Some biomechanists suggest that prosthetic limbs give Paralympians an unfair advantage, while others argued that prostheses restrict athletes as they power away from the blocks. 'When I saw Paralympians using these devices I said, "I really want to understand how these prostheses function during sprinting"', recalls Paolo Taboga, from the University of Colorado, USA. All of the previous studies had investigated sprinters running straight, however, 200 m and 400 m competitions are run on curves. 'We wanted to see what happens for these athletes with unilateral [one-sided] amputations when they run on a curve', explains Taboga, who teamed up with Rodger Kram and Alena Grabowski to learn more about the effects of prostheses on cornering. The team publishes their discovery that Paralympic sprinter that run with a left leg prosthesis are impaired when they sprint in the inside lanes of athletics tracks over 200m and 400m and they suggest that this impairment could impact on the result of Paralympic races. They publish their discovery in Journal of Experimental Biology at http://jeb.biologists.org.

However, instead of testing local recreational runners, the scientists aimed for the top and recruited members of the US and German Paralympic teams. 'It's like in Formula 1 races - you push the limits of cars', smiles Taboga, who wanted the athletes to give their prosthetic limb the ultimate workout as they sprinted around a flat curve on an indoor track.

The scientists flew athletes with left and right below-the-knee amputations to the University of Colorado Boulder, where they asked the sprinters to run at top speed around a 17.2 m radius curve in both the clockwise and anti-clockwise directions as they filmed the trials. Taboga admits that running around the clockwise curve was challenging. 'Nobody trains to run in that direction, so it is a bit weird', he says, remembering that everyone eventually got the knack of it.

However, when the team analysed the sprinters' performances, they were surprised to discover that the athletes that were running with their prosthesis on the inside of the curve were 4% slower than the athletes that were sprinting with the prosthesis on the outside. 'It was a measurable difference', says Taboga, adding that this could add up to two-tenths of a second to a sprint over 200 m. 'That means you could win the race, or get fourth and not even get on the podium', shrugs Taboga.

Admitting that the extent of the impairment was unexpected, Taboga explains that Paralympic sprinters produce less force when running straight, which probably means that the force is also reduced when they go around a bend. In addition, the athletes slowed more as they took the curve with the affected leg on the inside. 'So you have two limiting factors that sum up', he says. And when he broke the news to the athletes, Taboga recalls, 'A lot of athletes with a left leg amputation said, "Oh yes, when I have to run on curves I don't really like running in lane 1 or 2"'.

But what does all this mean for sprinters competing at the next Paralympic Games? Taboga suspects that athletes with a left leg amputation may be slightly disadvantaged, although he adds 'The calibre of the athletes is the main difference'. He suggests, 'To make a fair competition, let the left leg amputees run on the outside, lanes 5-8'. And he is keen to design new prosthetic limbs that handle corners better. 'Then people who don't normally like prostheses will use them more and get more active, improving their quality of life', he hopes.

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REFERENCE: Taboga, P., Kram, R. and Grabowski, A. M. (2016). Maximum-speed curve-running biomechanics of sprinters with and without unilateral leg amputations. J. Exp. Biol. 219, 851-858

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