At 8 a.m., before the day turns shirt-clinging muggy, bystanders gather in hopes of seeing some of the world’s really fast runners, soon to appear on the outdoor course for training sprints. A boy a bit bigger than his backpack fidgets against the railing, but the rest of the small crowd stands quietly, cameras ready. From behind a grassy rise on the far side of the course comes the slamming of metal doors, and suddenly the runners lope into sight, their long yellow tails kinked behind them.
Travel costs being what they are these days, this report on what makes an athlete extraordinary is not brought to you from Beijing. Instead, a $1.35 fare (off-peak) on the Washington, D.C., subway leads from the Science News offices to the grounds of Smithsonian’s National Zoo.
That’s fine actually. The zoo has the better athletes by far. In this assemblage of contestants in a physiologist’s fantasy Olympics, plenty of species can outrun, outdistance, out-hop and out-scurry poor old Homo sapiens. And researchers around the world are analyzing how these alternative gaits work and why some are so fast.
The zoo really does arrange morning training sprints for its cheetahs, but not at the top speed recorded for the species. The restriction comes in part from concerns for safety on the running path. A cord moving along a series of ankle-high guideposts pulls a lure in a snaking path through the domain of the three young cheetah brothers out today. The cord curves between clumps of tall grass and swerves around a perching log. With all these switchbacks to keep the exercise interesting, “acceleration is no problem; stopping is a problem,” says zoo cheetah biologist Craig Saffoe. So for a cheetah on the longest straightaway in the course, Saffoe keeps the speed lively but still safe, no more than 20 meters per second (about 45 miles per hour) — a speed that would smash world records in Beijing.
Of course, these cheetahs will race after a little swatch of rabbit fur on a motorized string. So there’s some consolation in remembering who controls the motor.
Run, Spot, run
An animal sprinting along a measured course marks a high point for testing animal abilities. “Many of the animal speeds given in encyclopedias, et cetera, are little better than guesses,” laments longtime locomotion researcher McNeill Alexander of the University of Leeds in England.
Even speeds timed on a measured course have their limitations, as does Alexander’s report of 7.5 m/s (almost 17 mph) for a white rhino at a briskish run, he acknowledges. The measurement derives from video that Alexander shot of the 2-ton-plus rhino being urged forward, respectfully, by a Jeep. That’s almost certainly not the top speed for the animal, he cautions. “You’re not going to hassle a rhino too much.”
Despite Alexander’s general skepticism about speed measurements, he does accept the cheetah as probably the fastest known running species. The measurement he finds most reliable, 29 m/s (about 65 mph), comes from a 1997 record along a 200-meter course clocked by an experienced timekeeper for athletic races.
Cheetahs in the wild hunt by stalking their prey and then sprinting after it in a brief blur. Saffoe says cheetahs can accelerate to 20 m/s (45 mph) in 2.5 seconds.
To see if he can inspire a little sprint this morning, Saffoe sets the cord humming around the course as soon as the cheetah brothers appear. The fur swatch flicks invitingly along the straightaway, but the brothers ignore it , trotting along a corner of the fence with a view of a female cheetah next door. After some long looks, the brothers turn to their own yard, where there are logs to be sniffed and marked, and — Hey! Small fleeing fur! One brother starts after it nose down, his stride lengthening.
The lure swerves back into the high grasses, and a different brother takes up the chase as it emerges. Saffoe has the lure burning down the straightaway now, but the cheetah appears casual — not even trying — as his long legs close some distance.
The cheetahs look skinny, but Saffoe says that much of their sprinting muscle is found on their backs. Disproportionately large hearts and even large nasal passages feed extra oxygen to those muscles.
After several minutes of Saffoe’s best feints and dodges, the brothers lose interest and flop in the shade, twitching their tails and waiting for breakfast. At best, Saffoe estimates, we saw a burst of a little more than 13 m/s (30 mph), not fabulous for a cheetah but fast for other species. At the lesser pace of 10.29 m/s, Jamaican runner Usain Bolt sprinted 100 meters in 9.72 seconds in May, challenging the human world record.
At least some humans can outrun small rodents. Alexander awards an honorable mention to the kangaroo rat, which is quick for its size. No relation to kangaroos, the little handful of fur is faster than a somewhat annoyed rhino and can hop at 8.9 m/s (almost 20 mph).
Alexander himself sounds somewhat annoyed at the mystique surrounding another supposedly prodigious hopper, the flea. “Do not be impressed by popular books that compare a flea’s 30-centimeter jump to a man jumping over St. Paul’s Cathedral,” he says. “Theory tells us that jump height should not fall in proportion to body size as animals get smaller.… Fleas are actually rather poor jumpers.”
Fakes, goes left
A stroll eastward from the cheetahs’ home reveals some underappreciated terrestrial runners: flightless birds.
In a shaded outdoor pen, two rheas step delicately around their bathtub-sized pond. Tall as people, they’re mostly legs and necks. Their cocoa-brown, egg-shaped bodies look startlingly wide, almost precarious, on such long legs.
Odd as a leggy flightless bird’s body plan looks to a human, it works well for running. Ostriches, for example, can sprint about as fast as horses. Alexander has timed an ostrich keeping pace beside his Jeep at 17 m/s (38 mph). And the birds prove nimble, switching directions while running at speed, says Devin Jindrich of Arizona State University in Tempe.