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Why We're Motivated to Exercise. Or Not. »

To what extent someone’s motivation to exercise is affected by genes has been hard to determine. Now a study in rats suggests that portions of the brain that control reward behavior may play a role in the decision to work out, or to remain on the couch.

Should Oscar Pistorius’ Prosthetic Legs Disqualify Him from the Olympics? By Rose Eveleth

Image: Wikimedia Commons/Erik van Leeuwen

Runners who’ve faced off against Oscar Pistorius say they know when the South African is closing in on them from behind. They hear a distinctive clicking noise growing louder, like a pair of scissors slicing through the air—the sound of Pistorius’s Flex-Foot Cheetah prosthetic legs.

It’s those long, J-shaped, carbon-fiber lower legs—and the world-class race times that come with them—that have some people asking an unpopular question: Does Pistorius, the man who has overcome so much to be the first double amputee to run at an Olympic level, have an unfair advantage? Scientists are becoming entwined in a debate over whether Pistorius should be allowed to compete in the 2012 London Games.

Pistorius was born without fibulas, one of the two long bones in the lower leg. He was unable to walk as a baby, and at 11 months old both of his legs were amputated below the knee. But the growing child didn’t let his disability slow him down. At age 12 he was playing rugby with the other boys, and in 2005, at age 18, he ran the 400-meter race in 47.34 seconds at the South African Championships, sixth best. Now 25, the man nicknamed the “Blade Runner” has qualified for the 2012 Summer Olympics in London, just three weeks before the games were to begin. But should he be allowed to compete?

The question seems preposterous. How could someone without lower legs possibly have an advantage over athletes with natural legs? The debate took a scientific turn in 2007 when a German team reported that Pistorius used 25 percent less energy than natural runners. The conclusion was tied to the unusual prosthetic made by an Icelandic company called Össur. The Flex-Foot Cheetah has become the go-to running prosthetic for Paralympic (and, potentially Olympic) athletes. “When the user is running, the prosthesis’s J curve is compressed at impact, storing energy and absorbing high levels of stress that would otherwise be absorbed by a runner’s ankle, knee, hip and lower back,” explains Hilmar Janusson, executive vice president of research and development at Össur. The Cheetah’s carbon-fiber layers then rebound off the ground in response to the runner’s strides.

After the German report was released, the International Association of Athletics Federations (IAAF) banned Pistorius from competing. Pistorius hired Jeffrey Kessler, a high-powered lawyer who’s represented athletes from the National Basketball Association and National Football League. It soon became clear that the IAAF’s study was very poorly designed, so when Pistorius’s team asked for a new study they got it. Soon scientists gathered at Rice University to figure out just what was going on with Pistorius’s body.

The scientific team included Peter Weyand, a physiologist at Southern Methodist University who had the treadmills needed to measure the forces involved in sprinting. Rodger Kram, at the University of Colorado at Boulder, was a track and field fan who studied biomechanics. Hugh Herr, a double amputee himself, was a renowned biophysicist. The trio, and other experts, measured Pistorius’s oxygen consumption, his leg movements, the forces he exerted on the ground and his endurance. They also looked at leg-repositioning time—the amount of time it takes Pistorius to swing his leg from the back to the front.

After several months the team concluded in a paper for The Journal of Applied Physiology that Pistorius was “physiologically similar but mechanically dissimilar” to someone running with intact legs. He uses oxygen the same way natural-legged sprinters do, but he moves his body differently.

Read on…

Running barefoot is better, researchers find. By Katherine Harmon

running barefoot better than shoes Mother Nature has outpaced science once again: the bare human foot is better for running than one cushioned by sneakers. What about those $125 high-tech running shoes with 648 custom combinations? Toss ‘em, according to a new study published online January 27 in the journal Nature (Scientific American is part of Nature Publishing Group).

“Most people today think barefoot running is dangerous and hurts,” Daniel Lieberman, a professor of human evolutionary biology at Harvard University, said in a prepared statement. “But actually you can run barefoot on the world’s hardest surfaces without the slightest discomfort and pain…It might be less injurious than the way some people run in shoes.”

Lieberman and his group used 3-D infrared tracking to record and study the running and strike style of three groups of runners: people who had always run barefoot, people who had always run with shoes, and people who had switched from shoe to shoeless.

They found that when runners lace up their shmancy sneakers and take off, about 75 to 80 percent land heel-first. Barefoot runners—as Homo sapiens had evolved to be—usually land toward the middle or front of the food. “People who don’t wear shoes when they run have an astonishingly different strike,” Lieberman said.

Without shoes, landing on the heel is painful and can translate into a collision force some 1.5 to 3 times body weight. “Barefoot runners point their toes more at landing,” which helps to lessen the impact by “decreasing the effective mass of the foot that comes to a sudden stop when you land,” Madhusudhan Venkadesan, an applied mathematics and human evolutionary biology postdoctoral researcher at Harvard who also worked on the study, said in a prepared statement. But as cushioned kicks have hit the streets and treadmills, that initial pain has disappeared, and runners have changed their stride, leading to a way of high-impact running that human physiology wasn’t evolved for—one that the researchers posit can lead to a host of foot and leg injuries.

Perhaps it should come as no surprise that our bodies are still better engineered than new-fangled trainers. When taking into account our ancient ancestors, “humans have engaged in endurance running for millions of years,” the researchers wrote in their study. “But the modern running shoe was not invented until the 1970s.”

Another recent study, by the American Academy of Physical Medicine and Rehabilitation and published last December in the academy’s journal, PM&R, found that wearing running shoes “increased joint torques at the hip, knee and ankle,” when compared to barefoot running. Even a jog in high heels was better for joints than specialized tennis shoes.

Despite the growing movement of barefoot (or more lightly shod) runners, many researchers are calling for more evaluation before all those sweaty sneakers are abandoned. “There is no hard proof that running in shoes… causes injuries,” William Jungers, a professor of anatomical sciences at Stony Brook University in Long Island, NY, wrote in a commentary that accompanies the new study. But, he asserted, “In my view there is no compelling evidence that it prevents them either.” And as a boost to the barefoot argument, he added: “There are data that implicate shoes more generally as a plausible source of some types of chronic foot problems.”

So perhaps you can skip those sneaks, say the study authors. “All you need is a few calluses,” Lieberman said.

Image comparing the footfall of two Kenyan runners from the study courtesy of Benton et al. The runner on the left has worn shoes most of his life and lands on his heal, whereas the runner on the right has primarily run barefoot and lands on the ball of her foot.

All Men Can’t Jump. By David Stipp

Why nearly every sport except long-distance running is fundamentally absurd.

Women's marathon during day one.

The women’s marathon at the 13th IAAF World Athletics Championships on Aug. 27, 2011, in Daegu, South Korea.

By Chris McGrath/Getty Images.

At first glance the annual Man vs. Horse Marathon, set for June 9 in Wales, seems like a joke sport brought to us by the same brilliant minds behind dwarf tossing and gravy wrestling. It was, after all, the product of a pints-fueled debate in a Welsh pub, and for years its official starter was rock musician Screaming Lord Sutch, founder of the Official Monster Raving Loony Party. But the jokiness is misleading: When viewed through science’s clarifying lens, the funny marathon is one of the few sports that isn’t a joke.

Hear me out, sports fans—I’m a basketball nut myself, and so the joke is as much on me as anyone. To see where I’m coming from, you can’t do better than examining basketball’s most physically talented player, Michael Jordan. He was hailed as nearly repealing the law of gravity, and during his prime he made rival players look as if they were moving in slow motion. But Air Jordan wasn’t in the same league as a house cat when it comes to leaping. Consider how casually young cats can jump up onto refrigerators. To match that, a man would have to do a standing jump right over the backboard. And a top-notch Frisbee dog corkscrewing through the air eight feet up to snag a whizzing disc makes Jordan look decidedly human when it comes to the fantastic quickness, agility, strength, and ballistic precision various animals are endowed with.

There’s no denying it—our kind started substituting brains for brawn long ago, and it shows: We can’t begin to compete with animals when it comes to the raw ingredients of athletic prowess. Yet being the absurdly self-enthralled species we are, we crowd into arenas and stadiums to marvel at our pathetic physical abilities as if they were something special. But there is one exception to our general paltriness: We’re the right honorable kings and queens of the planet when it comes to long-distance running.

The Wales marathon has helped demonstrate that. Its originator was a Welsh pub owner named Gordon Green. One day in 1979 he got into an argument with an equestrian friend about the relative strengths of men and horses as distance runners. Green insisted a human could beat a horse in a long race, and to prove his point he helped instigate the marathon in 1980. For the next 24 years, he found himself losing the argument as riders on horseback left human runners behind. But then it finally happened—in 2004 a British man named Huw Lobb won. Three years later Germany’s Florian Holzinger outran the horses, as did one other human contestant. The media loved it—a predictable farce had become a man-bites-dog story. Bookies were less enthused; they had to pay out on bets made at 16-to-1 odds favoring the horses.

The oddsmakers would have known better if they’d been following the work of Harvard anthropologist Daniel Lieberman and University of Utah biologist Dennis Bramble. They jointly proposed in a 2004 paper that we’re superlatively endowed by evolution to go long. Our long-striding legs are packed with springlike tendons, muscles, and ligaments that enable us to briefly store elastic energy as we come down on a foot and then recoil to help propel us forward. Tellingly, the most important of these springs, our big, strong Achilles tendons, aren’t found in early human precursors such as Australopithecus—it seems that the high-end tendons evolved along with other adaptations for distance running in the genus Homo when it appeared on the African savannah about 2 million years ago.

We’ve inherited large leg and foot joints from those ancestors, which spread out high forces that must be absorbed when running. To help ensure stability on two legs, we have big gluteus maximus muscles. (Chimps, which are incapable of distance running, have comparatively tiny butts.) Our clever torsos are designed to “counter-rotate” versus the hips as we run, also aiding stability. And we have an unusually large percentage of fatigue-resistant, slow-twitch muscle fibers, which make for endurance rather than speed. By contrast, most animals are geared for sprinting because they’re either predators that chase or prey that run away, and their muscles thus have much higher percentages of fast-twitch fibers than ours. (Cheetahs’ hind-leg muscles are the fast-twitch-richest of all.)

But what most sets us apart as runners is that we’re really cool—we naked apes are champion sweaters and can dissipate body heat faster than any other large mammal. Our main rivals for the endurance-running crown fall into two groups: migratory ungulates, such as horses and wildebeest, and social carnivores, such as dogs and hyenas. They can easily out-sprint us by galloping. But none can gallop very far without overheating—they largely rely on panting to keep cool, and they can’t pant when galloping, for panting involves taking very rapid, shallow breaths that would interfere with respiration when running. Dogs can gallop for only about 10 to 15 minutes before reverting to a trot, and so their distance-running speed tops out at about 3.8 meters per second. Horses’ average distance-running speed is 5.8 meters per second—a canter. Wildebeests’ is 5.1 meters per second.

Elite human runners, however, can sustain speeds up to 6.5 meters per second. Even run-of-the-mill joggers typically do between 3.2 and 4.2 meters per second, which means they can outrun dogs at distances greater than two kilometers.

Our “sustainable distance” is also hard to beat. African hunting dogs typically travel an average of 10 kilometers a day. Wolves and hyenas tend to go about 14 and 19 kilometers, respectively. In repeated distance runs, horses can cover about 20 kilometers a day. Vast throngs of human runners, by comparison, routinely run 42.2-kilometer marathons in just a few hours, and each year tens of thousands of people complete ultra-marathons of 100 kilometers and longer. (A few animals can match that under special circumstances. Huskies can trot up to 100 kilometers in Arctic conditions when forced to by people. But in warmer climes—no way.)

Given all this, you might wonder why it took so long for a human to win the Man vs. Horse Marathon. For one thing, the world’s top runners rarely compete in oddball races in rural Wales. And the 22-mile run (the Welsh race is shorter than the standard 26.2-mile marathon) through a damp, shady landscape doesn’t usually heat-stress horses much, thus largely negating the human runners’ edge. (Not surprisingly, the weather has been notably warm when men prevailed.) Human runners, by the way, have also sometimes won the annual Man Against Horse Race in Prescott, Ariz., in which contestants clamber up and down a mountain on 50 miles of rocky trails.

But how did we get this way? After all, our brainy, tool-using ancestors could have just sneaked up on prey animals and brought them down with a spear or arrow. Why did evolution shape us as great distance runners?

The answer, argue Lieberman and Bramble, is that snares, nets, and really effective projectile weapons, such as the bow and arrow, were probably invented by Homo sapiens—modern humans. There’s no evidence that early Stone Age hunters had weapons much better than sharp sticks. Such armaments would have required them to kill prey animals at close quarters, where they would have been at high risk of getting fatally gored, bitten, or kicked. Thus, they probably obtained meat mainly via “persistence hunting”—chasing an antelope, for instance, until it was nearly keeling over with heat exhaustion—and scavenging. The latter was very much a running game: When distant, circling vultures tipped them off about a lion kill, they had to get there before hyenas, which strip everything edible from carcasses. And they typically could only outrace hyenas in the hot sun. As a result, they carved out a new carnivore niche: the hot-day meat chaser.

Intriguingly, existing hunter-gatherers still sometimes resort to persistence hunting in hot weather. That’s because the nutritional payoffs can greatly exceed the energy costs of running down meat for us fleet-footed types. In fact, our ancestors’ meat-rich diets probably contributed to the evolution of modern human traits, such as small guts, small teeth, and big brains.

Elaborating on this idea, Mark Mattson, a neuroscientist at the National Institute on Aging, has proposed that our kind evolved superior smarts partly because they helped us record and recall the complex details we encountered when running after food—landmarks, tracking clues, location of water sources, and so on. The fact that endurance exercise is known to stimulate neuronal growth in the brain’s memory-forming hippocampus suggests he’s right. A relatedrecent study also suggests that natural selection endowed us with the ability to experience the “runner’s high,” wiring the brain so that endurance exercise lights up its “endocannabinoid” system in a pleasurable way to reinforce a tendency toward high-intensity running.

In sum, you might say we were born to run. But you also might just as well say we ran to be born. Come to think of it, that would make a seriously good motto for the Wales marathon.