Elephants' legs 'work like wheels of 4x4s'
Elephants have legs that work like the wheels of a Land Rover, scientists have found.
The "four-leg-drive" system means power is applied independently to each limb.
All other four-footed animals are thought to be designed with "rear-leg-drive". They tend to accelerate with the hind limbs while using their forelegs more for braking.
Study leader Dr John Hutchinson, from the Royal Veterinary College, London, said: "We have developed some new techniques for looking at animal movement that may change the way that we view the locomotion of other animals.
"We have shown that elephant legs function in very strange and probably unique ways. We even overturned some of our own previous ideas about elephants, which is always initially disheartening but ultimately exhilarating for a scientist.
"Our measurements have also provided basic data that will be useful in clinical studies of elephants, such as common lameness problems."
It used to be thought that all four-legged animals divide labour between their legs, using forelegs more for braking and hind legs for acceleration.
But this was found not to be true of elephants. Measurements of forces on the animals' legs at walking and running speeds showed that each limb was used both for accelerating and braking.
Elephants' legs were also shown to be slightly compliant or "bouncy", especially when running at faster speeds.
Experts had previously assumed elephants would need rigid "pillar-like" legs to support their weight. Bounciness made their legs two to three times less mechanically efficient than expected, putting them on a par with those of humans.
Just as in humans, muscle forces in elephants have to increase as their limbs become more flexed. Consequently running is 50% more costly than walking, which is why elephants are slower than many other animals.
The scientists wrote in the journal Proceedings of the National Academy of Sciences: "Surprisingly, elephants use their forelimbs and hindlimbs in similar braking and propulsive roles, not dividing these functions among limbs as was previously assumed or as in other quadrupeds.
"Thus, their limb function is analogous to four-wheel-drive vehicles. To achieve the observed limb compliance and low peak forces, elephants synchronise their limb dynamics in the vertical direction, but incur considerable mechanical costs from limbs working against each other horizontally."
The researchers analysed the movements of six juvenile Asian elephants using an advanced 3D motion-capture technique.
Reflective markers placed at strategic points on the elephants' bodies were filmed by seven infrared cameras and their changes in position fed into a computer.
The elephants were ridden or guided by their "mahouts" across their whole range of speeds along a walkway rigged with force-sensitive platforms.
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