Right-leg prostheses give sprint para-athletes an edge on bends

2019-03-07 11:04:02

Michael Steele/Getty By Chelsea Whyte Paralympic sprinters with left-leg prostheses should cross their fingers for an outside lane in the 200- and 400-metre races in Rio this August. That’s because the maximum running speed of para-athletes with single prostheses is slowed enough on tighter curves to affect the medal table. Because all track competitions are run in an anticlockwise direction, it’s the lefties that are at a disadvantage. Paolo Taboga, a biomechanist at the University of Colorado in Boulder, studied this effect in both non-amputees and runners with amputations below the knee. They found that sprinters wearing prostheses ran 3.9 per cent slower when their affected leg was on the inside compared with the outside of the curve. “We didn’t expect such a large effect,” says Taboga. “Four per cent is not a trivial difference for sprinters who compete in the Paralympic Games. It can mean winning or losing.” Using a high-speed camera, Taboga recorded 17 runners – non-amputees and those with both right- and left-leg amputations – sprinting as fast as possible on straight sections of a track and both clockwise and anticlockwise around curves. The runners with amputations were members of the German and US Paralympic teams, each of whom used a J-shaped carbon-fibre blade on their affected leg. The fastest runners are those that can exert the most force on the ground in the shortest possible time. All the athletes ran slower around the curves than the straight sections, with both amputees and non-amputees spending more time in contact with the ground with their inside compared with their outside leg. The runners with prostheses were also slowed by their ability to generate force with their affected leg when it was on the inside of the curve. Running prostheses create significantly less force than biological legs largely because they are lighter than muscle. Taboga says another factor that slowed the Paralympian participants was their prostheses’ inability to redirect ground forces. “You need to direct forces in the direction you want to accelerate, towards the curve on a track. A biological ankle can flex in all directions. These prostheses can’t do that,” he says. Since Oscar Pistorius entered the Olympic scene, there has been much discussion on whether prosthetics give any advantage or disadvantage to a runner, says Craig McGowan, a biomechanist from the University of Idaho in Moscow. But research has mostly focused on what he calls the “easiest part of the sprint” – the straight sections at top speed. Track and field athletes who run in 200- and 400-metre events encounter one or two curves, and those with prostheses face their biggest challenges on the blocks before they start and in handling corners. So how can Paralympic sprinters with left leg prostheses get a level playing field? Taboga suggests that they should be placed in the outer lanes for races. McGowan has another idea: “Knowing that there is a disadvantage to having a particular side with the prosthesis, you could run either way, maybe in different heats. There’s nothing but tradition that compels runners to go counterclockwise.” Hopefuls to compete in the US Paralympic team in Rio de Janeiro, Brazil, include three men, all right-leg amputees, and two women, both left-leg amputees, a spokeswoman for the team told New Scientist. Richard Browne is the world-record holder over 100 and 200 metres, and Jarryd Wallace is also one to watch. UK favourite Jonnie Peacock is also a right-leg amputee. Journal reference: Journal of Experimental Biology, DOI: 10.1242/jeb.133488 More on these topics: