Well it’s rapidly approaching the time of year where everyone resolves to either diet, eat less, exercise more, or a combination of all three. As I decided to eat my body weight about five times over in roast dinners and multiple deserts in the last few days, this morning seemed like as good a time as any to start running again.
I’m always a little tentative when I start running after a few weeks off. Not just because I dread how unfit I’ve become, but because 2 years ago I had a hip operation. My hip just hasn’t been the same since then. Thing is, my injury is nothing compared to two amazing runners I worked with earlier this year.
They both have lost a leg.
Stephanie Reid and Jonnie Peacock are both 2012 Paralympic hopefuls, and both run with a specialised prosthetic limb commonly known as a blade or a cheetah limb. Most people may have come across these limbs when Oscar Pistoruis, who runs with two blades, petitioned to run in able-bodied races. Despite having no legs, many opposed him competing as they maintained that the specialised carbon fibre cheetah legs gave him an advantage; this remains controversial.
The use of cheetah legs is relatively new to the sporting world, having only been invented in the late1970s. Therefore, there is not a large amount of data and comprehensive research into the legs has really only just recently taken off. The turning point in running and sprinting prosthetics was when Ossur, one of the leading prosthetic manufacturers, introduced their Cheetah limb in 1996.
Before 1996 the flex-sprint, a basic everyday foot without the heel section, was used. The heel was removed so the shape and stance of the prosthetic mimicked a human limb whilst running – i.e. it was “up on the toes” leaning forward slightly. The Cheetah limb refined this by creating a shape that would absorb and release more energy in a more efficient manner.
In a running prosthesis, each time body weight moves over the flexible foot, it compresses and energy is stored. As body weight shifts off the foot, the foot returns to its original shape, returning energy as it decompresses. Measurement of the efficiency of the foot is based on similar physics to a simple spring. Unlike a prosthesis, the human ankle is not passive, it generates forces. Using the spring analogy, the human ankle is about 241% efficient. This is in stark contrast to prosthetic limbs; one data set showed only 84% efficiency for one of the top blades. However, recent advances and studies indicate that prosthetic technology, including development of dedicated sports prosthetics, mean that the efficiency of the prosthetics could be creeping closer to 100%.
Jonnie and Steph are just two athletes using these amazing running prosthetics. But because Steph has been training for more time, she has a more efficient running style.
When running, a symmetrical style is more efficient. This is difficult initially in an athlete who has lost a leg; the hip and the muscles in the upper leg and torso have to generate different amounts of force. Steph’s efficient style was revealed through analysis that I set up for Channel 4’s Inside Incredible Athletes at MMU’s biomechanics lab.
For both athletes running over a force plate revealed that the prosthetic vibrated when it hit the ground was in contact with the ground for a different amount of time to their intact limb. However, using specialist motion capture cameras revealed a greater asymmetry in Jonnie’s running style. He is young, so the style will become more symmetrical with time and training, and he will get faster and faster.
The human body has such a incredibly capacity for adaptation, illustrated beautifully through these two athletes. But they also show how much hard work and dedication to perfection is needed to achieve greatness.