Anyone who watched Ethiopia's Derartu Tulu win the 2009 New York City Marathon would agree: She was running. But what about high-speed elephants? Their five-ton frames preclude them from breaking into a bouncy jog, yet charging elephants can reach speeds on par with Tulu's. But are they running?

That question drove Belgium-based physiologist Norman Heglund to build an eight-meter-long platform equipped with 16 force-reading plates—each containing a complete computer system linked to a massive server—weighing a total of six tons. Heglund then shipped the enormous catwalk to the Thai Elephant Conservation Center in Lampang, Thailand. There, 34 elephants ranging from 872-kilogram baby named "Prayoungkeart" to a four-ton adult called "Kumlha" trod along the platform at paces varying from a leisurely 38-centimeter-per-second stroll to a rampant 4.97-meter-per-second charge. Using cameras to monitor the movement of each elephant's center of mass, Heglund's team was able to analyze the unique gait pattern of the biggest living terrestrial animal and obtain valuable information about the effects of body size on energy efficiency.

"Almost everything changes with body size," says Heglund, a professor at the Catholic University of Louvain in Belgium who has studied allometry, or size scaling, since graduate school. Take heart rate, for example: Humans have an average heart rate of 72 beats per minute, whereas the tiny hearts of mice race at a rate eight times faster. Big animals also consume less energy than smaller ones to do the same amount of work, Heglund says. But it was his interest how much energy big animals spend that made the elephant study so important. "The original idea was that energy output was independent of body size—that all animals did essentially the same amount of work per unit of body weight. But when you extrapolate that to big animals, it contradicts the theories of energy," he says.

Before 58-year-old Kumlha, the largest animal that Heglund had studied was a 200-kilogram pony back in 1988. Between the pony and a 2.9-gram white mouse, Heglund generated a speckled line of "mass-specific energy cost" data points from 14 other quadruped species. He extrapolated those points to create a sloped line of energy cost versus body weight. But even then he dreamed of elephants. "Any animal that's at one extreme of size or the other affects the slope of the line more than any in the middle. It's important for clarifying the allometric relationship between work done and body size," he says.

Heglund admits that it took a long time to amass the funds and expertise to carry out such a huge experiment. But the study, published February 12 in The Journal of Experimental Biology, provided important size scaling data, and some interesting observations about the way elephants move. Their "exceptional dimensions" make elephants relatively more fragile than smaller animals because of the force exerted on their supportive tissues. But these dimensions also make the elephants' movements extremely economical, with a mass-specific energy cost one third that of humans and one thirtieth that of mice. But whether they're walking or running, Heglund says, depends on what end of the elephant you're looking at. "If you look at their front legs, you might say that qualifies as a run. But if you look at their back legs, you could say they're just walking," he says. "It really depends on your definition of run."

Heglund's focus has now shifted from elephants to gravity—actually the lack of it. The Subject Loading Device for the International Space Station's "Colbert" treadmill, which holds a running astronaut in place during microgravity exercise, was his design. He insists the elephant study was basic research with "not a lot of human applications." But remember: photographer Eadweard Muybridge's answer to the debate over whether all four hoofs of a horse left the ground at the same time during a gallop led to the first motion picture.