Built for Speed

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.

Jindrich began studying the birds after examining cockroaches for a military-funded robot project. To analyze how the roaches coped with sudden jolts, he devised miniature jet-packs that he fastened onto the roaches’ backs. And to study maneuverability he borrowed an engineering technique for detecting stresses. “I was running cockroaches over Jell-O,” he says. Gelatin — he actually used unflavored brands — undergoes structural shifts when disturbed, changing the polarization of light passing through. Even the footfalls of roaches leave telltale signs for analysis. To compare maneuverability in a different kind of runner, Jindrich visited the Royal Veterinary College’s Hawkshead campus in England to experiment with eight ostriches. The birds hadn’t reached full adult size but already looked the 6-foot-1 Jindrich eye-to-eye. “Fortunately they were friendly birds,” he says. This was no job for Jell-O, though. The ostriches ran along a fenced runway and crossed a platform instrumented to measure the forces of foot stomps. Jindrich placed a box just beyond the platform so ostriches had to dodge the obstacle. The egg-shaped ostrich body is less likely to over-rotate during fast turns than humans’ more columnar body shape, he and his colleagues reported last year in The Journal of Experimental Biology. For an animal Olympics then, Jindrich muses about ostriches playing soccer. They do kick, he says. Albeit backward. Stand up and run Australia’s dragon lizards can run bipedally too, although they use four legs to walk. Or so says science. The three dragon lizards in the National Zoo, of the Pogona minor species, are using all of their legs to cling in perfect stillness to logs. The plastic-dinosaur immobility does offer a good chance to admire their skin, studies in grays and browns with delicate fringing around the strong-jawed heads. These lizards do move, says Christofer Clemente of the University of Cambridge in England. What interests him are the explanations for why four-legged walkers rear up on occasion to run. He and his colleagues caught species of the lizards, including P. minor, in Australia and set them running on a treadmill. Theorists had proposed that bipedal running was more efficient. Yet Clemente established that the lizards got exhausted sooner when they loped along bipedally than when moving on all fours. So he finds it unlikely that upright running saves energy for the lizards. Instead, Clemente is exploring an idea proposed in 2003 by Peter Aerts of the University of Antwerp in Belgium that ties lizard two-legged running to acceleration. During a rapid start, the upper body of the lizard would just leave the ground in a reptilian wheelie. The treadmill tests support this idea. Clemente measured lizard accelerations as high as 30 m/s/s, which he estimates roughly doubles a human sprinter’s bursts. Speedy pickup went with lifting up to run on two legs, he and colleagues report in the July 1 Journal of Experimental Biology. One scenario has lizards rearing upright as a side effect of a shift toward more maneuverable bodies. Less weight in the skull and front parts of the body would improve a lizard’s ability to turn on a pebble. Yet that light front end tends to lift off the ground during rocket-start acceleration. The side effect notion fit for one kind of lizard, which went bipedal when the acceleration model predicted it would. Other species, though, went bipedal at lower accelerations than physics would necessitate. These lizards seemed to be shifting their center of gravity behaviorally, by tucking in their arms or repositioning their tail. However fascinating his lizards are, Clemente acknowledges that they aren’t that fast. They manage only 5 to 6 m/s (12 mph or so). So he proposes an Olympics rule-change: measuring races in body lengths. A human athlete covers some six lengths per second. Dragon lizards would beat that — covering 30. Splash speeds No funny business with the rules is necessary for fantasy fish Olympics. “I have told my zoology class that we should put a Speedo logo on the side of an albacore in the Olympics and have it race,” says Frank Fish of West Chester University in Pennsylvania. His research focuses on dolphins and other aquatic animals, but he says he watches a lot of human competitive swimming. “I’m amazed at how pathetic human swimmers are compared to other animals,” he says. In March, Alain Bernard set a world record by swimming 50 meters at an average speed of 2.3 m/s (5.1 mph). Big tuna, Fish points out, can do 20 m/s (about 45 mph). Albacore and other tuna get the shape right, close to the teardrop that minimizes drag. Tuna, which cover huge distances on their migrations, pack a lot of high-powered aerobic muscle into that teardrop. Tuna represent an “extreme design” for a swimming animal, says Robert Shadwick of the University of British Columbia in Vancouver, Canada. They and some other fast predators like lamnid sharks have converged in highly streamlined bodies with muscles tuned for aerobic performance. In yellowfin tuna, the rippling muscles don’t bend the body so much as transmit power to the tail, Shadwick and Douglas Syme of the University of Calgary in Canada report in the May 15 Journal of Experimental Biology. Muscles and a system of tendons create strong, well-timed strokes of the tail fin for near-maximal power. Some hunting whales can sprint too. “Cheetahs of the deep sea” is what 
Natacha Aguilar Soto of La Laguna University in Tenerife, Spain, calls short-finned pilot whales in a paper published online April 28 in the Journal of Animal Ecology. Electronic tags on 23 whales tracked their diving behavior. In the deepest plunges, down as far as 1,019 meters, whales reached speeds of 9 m/s (20 mph), as if racing after prey. Like cheetahs, the pilot whales could be putting their energy into sprints after big targets. Jetting around At the zoo’s invertebrate display, zoo-goers can see swimmers taking a different approach. In two big, dimly lit tanks, chambered nautiluses the size of saucers bob gently against the glass. When they move, they squirt out gusts that drive them in the opposite direction by jet propulsion. utiluses are slow, but jet propulsion can be quite fast, says Hans-Otto Pörtner of the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany. The champions are the temperate-latitude, upper-ocean squid. The shortfin squid (Illex illecebrosus) and relatives have the sprint power to hunt with the fish. Pörtner calculates that jetting around so much takes five to 10 times the amount of oxygen that fishy swimming does. Also, “they’re not just the jet set; they’re blue bloods,” he says. When oxygenated, their blood turns blue with the reactions of hemocyanin molecules. These bulky oxygen-carrying molecules have only a third to a fifth of the capacity of the hemoglobin that does the same job in vertebrate blood. Offsetting these disadvantages, thin skin lets squid take in some 60 to 80 percent of their oxygen directly from surrounding water, Pörtner and colleagues have found. And the muscles that most need the oxygen lie just under the skin. Pörtner calls the shortfin squid “marine invertebrate athletes,” but he’s not daydreaming of squid Olympics. Any food will distract them, he says. “I don’t think you could keep them in the lanes.” Panda acrobats The most famous residents of the National Zoo aren’t swimmers, but they are visiting from the 2008 Olympic host country. Near the top of the zoo’s main hill sits a complex of boulder-filled yards inhabited by three pandas. For all their teddy bear looks, pandas do have strength and agility. Visitors rarely see it, but male pandas naturally back their rumps up to trees and then walk their legs up the trunk. Their short forelimbs are muscular enough for a male to back his rear legs so high he is doing a handstand, albeit with feet propped against a tree. It’s an extreme version of a dog at a fire hydrant. A handstanding panda leaves a urine trace on the bark as part of his species’ community bulletin board system. A hot, summer day in Washington doesn’t lend itself to handstands. Even the youngest of the pandas, 3-year-old Tai Shan, has moved to his indoor, air-conditioned apartment. He sprawls in a panda-sized dip on one of the indoor rocks, one paw hooked under his chin. So, in homage to the official Olympics and their host country, be it noted that a panda can flop in the shade and lounge as fast as any cheetah.