POSTED 17 APR 2003
Elephant animation at top, is based on the photography of Eadweard Muybridge: Elephant Ambling from Animal Locomotion, 1887
| In science,
big excitement can come from small questions. John Hutchinson can attest
-- the Stanford researcher and his colleagues have spent six years puzzling
away at a riddle that probably never vexed the great philosophers: Can elephants
They're quick, for sure. And most four-legged mammals are indeed runners. But big animals have trouble getting airborne, for obvious reasons. Elephants, the largest land mammals, can weigh more than four tons and have a surprisingly low ratio of muscle to body mass.
Original photo from U.S. Department of State.
Hutchinson made headlines last year when he announced that Tyrannosaurus Rex was probably not the spry athlete we'd imagined. So when he stumbled upon the work of fellow biomechanist Rodger Kram, he was naturally curious.
"[Kram] had found that elephants move most cheaply per unit distance of any animal on land," says Hutchinson. Simply put, the hulky beasts register the most miles per gallon. Still, elephants don't make the best lab animals, so how they move so efficiently has long been a matter of some dispute.
For instance, no one knew whether fast-moving elephants were walking or running, or doing something in between -- say, dancing an Irish jig. And certainly, no one knew exactly how fast an elephant could move. Some estimates ran upwards of 35 mph, although many researchers clung to a more conservative guess of about 10 mph.
Scientifically speaking, there are a number of ways to tell whether an animal runs. The classic definition is that running happens when all feet are off the ground during each stride. Recall the famous stop-motion pics taken by 19th century photographer Eadweard Muybridge. He showed that when running, horses lift all four legs simultaneously between steps.
Since Muybridge, theories about how animals move have been seriously refined. Three patterns dominate, among the four-legged set:
The walk, demonstrated by lumbering donkeys everywhere, in which each foot hits the ground at different times, and at no time are all feet in the air at once. It goes something like this: left hind foot, left front foot - pause - right hind foot, right front foot. There is another name for this pattern; if you want to impress friends (or possibly estrange them), ask if they feel like taking a singlefoot in lateral sequence with lateral couplets.
The trot, when the left hind and right front feet touch the ground almost simultaneously, followed by the right hind and left front. A fast trotter is airborne for a moment between these diagonal footfalls.
And, finally, the gallop, which has the two rear legs touching the ground together, followed by a brief airborne glide, and then a landing on the two front legs.
To see which sequence best described elephant movement, Hutchinson went to Thailand, following rumors that the southeast Asian country is home to some of the fastest captive elephants. Once there, his team asked local elephant trainers, called mahouts, to select the fleetest individuals from their camps.
The researchers dotted each elephant with paint at the shoulder and hip joints, and videotaped the hulking animals following a 100-foot course. Each elephant was clocked as it triggered beams of light at the beginning and endpoint of the course -- much as Olympic running times are measured in competition.
And the winner is...
Still, says Hutchinson, "we couldn't find any obvious evidence they were changing gait." Rather, the animals appeared to maintain a characteristic walk-like pattern, no matter the speed.
But of course, no scientist worth his name in ink would leave it at that. In biomechanics, knowing an animal's speed and footfall pattern is but a mediocre understanding of how it moves. So the team scrutinized each video -- watching when which foot fell where, and how fast - to find the deeper trends in their data.
Specifically, they wanted to know the fraction of time each foot was on the ground, compared to how long it took the animal to complete a stride -- to arrive at a number called the duty factor.
"We were surprised to find that elephants got to duty factor of .37, which is close to the point where all feet would have to move off the ground," says Hutchinson. "In a classical sense they didn't run. But in another sense, some people would define running by having a duty factor below .5."
As it turns out, elephants have evolved an efficient way of moving that capitalizes on the low-impact benefits of walking and the spring-like step of a run.
I meant what I said, and I said what I meant.
The hip and shoulder joints are stable, which means they don't change position relative to each other. As a result, they show how the center of mass is moving. When running, says Hutchinson, an animal's center of mass should be lowest at the step's midpoint.
During walking, the elephants' hip and shoulder joints both went up and then down. But at very fast speeds, the shoulders maintained that pattern but the hip joints went down and then up. In other words, the rear limbs acted like springs.
"Walking is like a toy soldier's stiff-legged gait. Your limbs stay straight. And during running, it's different. The limb compresses while the foot is on the ground, like a pogo stick," Hutchinson says.
It's a subtle difference, and until now no one had studied elephant motion enough to describe it very well.
"We show some hints that elephants are running, but I don't think we've totally nailed it down," Hutchinson says. The only way to be certain is to measure the forces the animal exerts on the ground using a giant scale. The trouble is, no such scales exist for animals so hefty.
Photo: U.S. Fish and Wildlife Service.
"You need a scale that won't break when an elephant steps on it," Hutchinson says. "We haven't had access to such a device, so we're designing one."
-- Sarah Goforth
Hutchinson, J.R., Famini, D., Lair, R. & Kram, R. Are fast-moving elephants running? Nature 422, 493-494 (2003).