Researchers have uncovered why the ostrich, and perhaps the emu, can run the pants off a kangaroo. It comes down to a literal spring in the flightless bird's step.
A team of Australian and US scientists has found the ostrich uses its tendons to store and return twice as much elastic energy per step than humans, reducing the amount of effort required by their muscles.
The findings may be critical in the development of better prosthetic limbs and orthotics and in helping engineers design more agile and mobile robots, Dr Jonas Rubenson, of the University of Western Australia says.
Rubenson, an assistant professor in the School of Sports Science, Exercise and Health, says the aim of the study was to discover the mechanical adaptations made by species that are adept at running economically.
"Cheetahs and lions are great sprinters, but they use a lot of energy when moving," he says. "However ostriches, horses and antelopes are adapted to running fast and economically over long distances."
Rubenson says previous work had shown the ostrich uses 50% less energy running when compared with humans, yet can run at twice the speed.
He says there were two common explanations to explain this economy of running in animals. The first suggested it was dependant on the mechanical action used in swinging limbs, while the second hypothesis claimed these animals could store a lot more elastic energy in their joints.
Their current study involved gait analysis and motion analysis of limb swing in both humans and ostriches. The researchers also measured the forces animals applied to the ground while running.
Keeping the ball rolling
The results showed ostriches and humans generated the same amount of mechanical power to swing limbs, but showed a marked difference in the storage and release of elastic energy in their tendons.
They estimate 83% more work is generated by the release of elastic energy in the ostrich joints during stance compared with humans. This means the ostrich needs to input much less energy to "keep the ball bouncing".
"This saves the animal metabolic energy, so they don't get as tired," says Rubenson.
The study used ostriches as they have a similar mass to humans, but Rubenson believes the finding will also apply to the lighter, Australian emu.
He says the findings show better prosthetic design should focus on elastic propulsion. It may also help resolve the argument over whether South African sprinter Oscar Pistorius has an unfair advantage with his carbon fibre prosthetic blades.
"What they have done is tap into the concept of storing elastic energy," he says. "Yes he has a good limb design, but he is still has a disadvantage because he has a large proportion of muscle mass missing."