A spring in its step: at top speed, an elephant does not run—by traditional standards—but it doesn't walk either

Natural History, May, 2007 by Adam Summers

Do elephants run, or just walk briskly? According to many biomechanists--and the judges of Olympic racewalkers--an animal is running, not walking, when at some point in each stride all of its feet--two or four of them--are off the ground at once. Of course, for anyone who has faced charging elephants, the semantics of such things don't much matter: running or walking, a herd of elephants can cause heart palpitations. But the question is still worth asking, because when it comes to the way elephants move, the traditional distinction between running and walking isn't very informative. Besides going airborne, what else might mark the transition from amble to jog?

For openers, think about what happens when you take a leisurely walk. With each step, you plant a relatively straight leg on the ground. Then your forward motion swings your hip and your center of gravity up and over the highest point of an are centered on your foot. So a walking leg is like an upside-down pendulum, and your hip rises to its highest point in mid-stance.

Running is almost the reverse. When all your weight is on one foot, in mid-stance, your hip dips to its lowest point in the running cycle. That difference in hip position reflects a fundamental difference in the way energy is transferred and stored. Instead of transferring forward momentum into driving an inverted pendulum, your leg, in running, acts like a coiled spring. First it compresses, storing the energy of your body's falling mass as your foot lands on the ground. Then your leg rebounds, releasing the stored energy and propelling your body upward and onward.

You might think that by now biologists would know full well how pachyderms prance. In fact, though, there are surprisingly few believable measures of their top speed, much less clear conceptions of the gait by which they max out. In fairness, studying the motion of fast-moving elephants poses difficulties and dangers. Zoo elephants make poor study subjects, simply because they have already been selected for being unlikely to zoom around their enclosures at high speed. And there aren't many places where elephants can be safely raced for a substantial distance in a straight line. John R. Hutchinson, a biomechanist at the Royal Veterinary College in London, and his collaborators faced those challenges with a video camera, experienced mahouts, and an international array of elephants--ranging from yearlings to sixty-year-old mommas--to determine whether elephants do more than walk.

Hutchinson and his colleagues painted white dots on the hips and shoulders of both Asian (Elephas maximus) and African (Loxodonta africana) elephants, and then videotaped them under controlled conditions in Asia, Europe, and North America. The results debunked reports that some elephants could move at an astonishing twenty-five miles an hour. The top measured speed was about fifteen miles an hour--still quite brisk, but no faster than a reasonably fit person could run in terror.

What about running? Hutchinson clearly demonstrated that at no time does the entire elephant leave the ground. The animal does get three feet off the ground at once, but an Olympic judge for racewalking would still be happy with that gait. Hutchinson points out, however, that by other definitions, Jumbo is running.

Video analysis of the white dots of paint shows that in slow gaits the elephant's hip rises after the foot is planted, just as it does in a walking person. In the fast gait, however, the hip continues falling after footfall, and rebounds before the toe comes off the ground. That is consistent with the idea that the limbs are shifting from a pendulum-dominated walking gait to a springy run [see illustrations on these two pages]. Taken as units, the fast-moving forelimbs and hind limbs each have an aerial phase, so you could say that both ends of the elephant run, but not at the same time. (Work not yet published by Hutchinson indicates that the shoulders don't undergo the same springlike compression as the hips, though.)

You might think that the elephant s peculiar way of "running" arose solely because of its huge size. But consider the white rhinoceros, the second-largest land animal, which can weigh more than 5,000 pounds. That's half as much as an adult African elephant. Yet the rhinoceros runs exactly like a horse--a really big, nearly blind, very grumpy horse. All four of its feet leave the ground, springing the behemoth forward from step to step.

Compare that with the gait of a baby elephant. A month-old baby, with a sprightly weight of 250 pounds, is fully able to charge along as fast as its full-grown parents--often a little faster. But it never goes airborne. The anatomy of elephant legs may simply not be suited to aerialism, or perhaps the running style is hardwired into the nervous system. But whatever the case, a growing elephant does not follow a progression of running styles from zebra-style to Cape buffalo to rhinoceros; it runs to type its whole life.

ADAM SUMMERS (asummers@uci.edu) is an associate professor of bioengineering and of ecology and evolutionary biology at the University of California, Irvine.