By Victoria Gill
Science and nature reporter, BBC News
Computer imaging reveals the spring in an ostrich's step
They may look ungainly, but ostriches are excellent runners.
Now scientists have discovered how the birds run so fast and, importantly, so efficiently.
Ostriches use half the energy that we humans need at our top running speed, say researchers, who made the discovery by comparing humans and ostriches in a running test.
The secret is their springiness - ostrich tendons store twice as much "elastic energy" per step than us.
The birds were fitted with markers so their movement could be traced
The results of this biomechanics experiment are described in the Royal Society journal Interface.
Five "very tame" ostriches were involved in the study; the scientists measured the movement of their limbs and joints and the force with which the birds' feet hit the ground.
The avian subjects ran on a purpose-built 50m (164ft) running track. They were fitted with reflective markers on their joints to allow their movement to be captured in detail.
Five human volunteers were studied in exactly the same way - with several cameras capturing them from different angles.
Professor Jonas Rubenson, from the University of Western Australia's School of Sport Science, Exercise and Health, led the study.
He said the findings could provide insight for biologists looking at the evolution of bipedalism, both in humans and in dinosaurs. They could also reveal some of the biological secrets of agility, which should ultimately inform the development of prosthetic limbs and even robots.
Despite their size and speed, wild ostriches have fallen prey to cheetahs
They chose to study ostriches because they are of similar mass to humans - this mass-matching allowed the team to draw comparisons between the ostrich and the human gait.
The team was surprised to find that ostriches and humans used nearly exactly the same amount of mechanical work to "swing" their limbs back and forth when running.