"Do Elephants Run?", Input/Output, ME Departments, June 2003

input/output

by Jean Thilmany, Associate Editor

do elephants run?

For all their cumbersome size and weight, elephants can move pretty fast: about 15 mph. Sure, elephants get speed up, but are they really running?

To the casual observer, it doesn't look that way. Even when the pachyderms move at 15 mph, their footfall pattern remains the same as when they walk. Never do all four feet leave the ground at the same time—a hallmark of running. But now biomechanists are finding that an elephant's center of mass appears to bounce at high speeds. If that turns out to be true, an elephant's gait meets the biomechanical definition of running.

The answer to whether elephants run or just walk really fast is an intriguing one for many biomechanists, because it might help to answer questions about how other large animals move.

Researchers dubbed the elephant's fast gait Groucho running—after Groucho Marx's crouched walk. Elephants seem to bend their limbs slightly in order to move their bodies smoothly. Research into the Groucho run might provide insight into biomechanical tricks that help large animals—from extinct dinosaurs to very overweight humans—overcome the physical forces that restrict their motion, said John Hutchinson, a mechanical engineering postdoctoral research fellow at Stanford University in Stanford, Calif.

To study how elephants travel at speed, John Hutchinson of Stanford University painted dots on their joints then videotaped them moving.

Last year, Hutchinson was part of a study that used a computer model of physical forces to show that Tyrannosaurus rex was probably too big to run quickly. For a recent look at elephants, he teamed with a veterinary student at the University of California, Davis; an adviser at the Thai Elephant Conservation Center, and an associate professor of kinesiology and applied physiology at the University of Colorado in Boulder.

They focused on an extant animal rather than an extinct one: a species of Asian elephant called Elephas maximum that can tip the scales at more than 3 tons. One member of the team, Rodger Kram, the associate professor of kinesiology, had noticed while studying elephants at the Six Flags Marine World in Vallejo, Calif., that the animals preferred to walk at a slow but efficient speed that gave them what he called the best gas mileage.

Hutchinson and Kram wrote to Richard Lair, who worked at the Thailand conservatory dedicated to saving Asian elephants from extinction.

"They asked if I thought Thai elephants could run faster than the speeds they got from U.S. zoo and circus elephants," Lair said. "I knew they could because I had timed them much faster."

Hutchinson and Dan Famini, the veterinary student, decided to put the elephants in Thailand to the test. For their experiments, they palpated the animals' limbs to find the joints, which they marked with large dots of nontoxic paint. They videotaped 188 trials of 42 Asian elephants walking and running through a 100-foot course and measured their speed with photo sensors and video analysis.

The animals walked at about 4.5 mph. But 32 of the elephants moved faster than previously documented—up to 15 mph. Three were especially fleet of foot, exceeding 15 mph, which is 50 percent faster than anyone had ever reliably recorded an elephant to move, Hutchinson said.

So these elephants were fast.

"I ran the mile in 4:30 back when I was in high school and I'm still a competitive master's runner," Kram said. "But I can only just barely sprint as fast as the fastest elephants that
we measured."

However, the researchers still needed to see if the elephants were actually running. Elephant footfall pattern was key. No matter how fast elephants move, their footfall pattern doesn't change, which is a rarity in the animal world, the researchers said. Even when they're traveling fast, elephants don't move through an all-aerial phase—where no feet are on the ground. The all-aerial phase differentiates running from walking.
Still, the researchers' kinematic measurements suggest that fast-moving elephants may switch from a pendulum-like gait to a bouncing gait, the Groucho run, which fits the biomechanical definition of running.

But there's only one way to find out for sure. The animals would have to move across a force platform—a special device that registers the forces that elephants exert on the ground—to see if their center of mass swings like an inverted pendulum, as in walking, or bounces like a spring, as in running.

"That's a problem, because the force platforms that are generally available would break if an elephant ran across them," Hutchinson said. "That's been the obstacle for years. That's one reason no one has ever done it."

He and Kram, however, are building a prototype force platform in Colorado to answer the question once and for all. Do elephants run? Place your bets now.