High heels and ostrich legs
11 May 2012 by Evoluted New Media
Women walking in extremely high heels exert the same force on the ground as a strutting ostrich and researchers believe this finding could help improve prosthetic lower limbs and robots’ legs.
Walking involves the repeated process scientists refer to as ‘crash, vault, push’ – the most economical way of walking. Researchers from the Royal Veterinary College believe that making limbs less human-like, and more like the leg of an ostrich could make prosthetics and robot limbs more efficient.
“Despite vastly differing arrangements of joints and hip wiggles, humans walking normally, women in extremely high heels and ostriches all produce strikingly similar forces when walking,” said Dr Tatjana Hubel. “This is the most mechanical way of walking.”
“We do everything we can to make the forces follow the same pattern, which is why – for example – women wiggle their bottoms when they are in high heels. The question for us is, why is the human foot shaped the way that it is and not, say, like an ostrich’s?”
When modelling the leg, scientists imagine a stick with a block body on top which moves like an inverted pendulum. In this model the shape of the foot makes no sense, but the human leg is more complicated than this. The shape of the foot means that when it is flat on the ground, all the force goes through the ankle, allowing muscles to support the weight of the body, while being largely unloaded during the vault stage.
Researchers believe their finding will have implications for the design of better prosthetic limbs for above-knee amputees and for the legs of humanoid robots. Dr Jim Usherwood said if you want to make a good prosthetic foot the motor –the ankle – should be placed as far up the leg as possible to provide power without making the foot heavy and hard to move.
“Some clever prosthetics copy the ankle and are very human-like, but for above-knee amputees, a typical prosthetic leg that is very human-like is heavy and hard to move around,” Usherwood said. “It’s much better to have an ostrich foot at the end of a very lightweight leg.”
Paralympic athlete Oscar Pistorius uses prosthetics like this – his blades have no heel, and are light and springy – optimised for running rather than walking.
