The shod Kenyan runner on the left strikes the ground with his heel, creating a rapid, large collision force, while the barefoot runner on the right lands on the ball of her foot, avoiding a high collision force. Credit: Benton et al.

To complete a recent study, a team of scientists left Boston and went halfway around the world, to the middle of Kenya. They wanted to find out more about barefoot running.

Sure, people can run barefoot anywhere. But the Rift Valley Province in Kenya has produced some of the most famous long-distance runners in history, and many of these athletes grew up not wearing shoes. With a video camera in hand, scientist Daniel Lieberman and his colleagues visited some of these runners to figure out what a difference shoes make.

It was a big difference, and not necessarily for the better. In particular, when a bare foot hits the ground, the blow is softer and the running motion smoother. This research suggests that running barefoot may have advantages over running with shoes on, though more studies are needed to determine whether or not barefoot running reduces the chance of injuries. Also, the team didn’t investigate whether there’s a difference for sprinting.

“One shouldn’t be scared of barefoot or minimal shoe running or think it odd,” Lieberman told Science News. “From an evolutionary perspective, it’s normal and, if done properly, it is very fun and comfortable. We evolved to run barefoot.”

Lieberman is an evolutionary biologist at Harvard University. An evolutionary biologist is a scientist who studies the way living creatures have changed over long periods of time. With his research, Lieberman wants to know why and how the human body works the way it does.

Previous studies have shown that when a person runs barefoot, she lands on the fronts or middles of the feet. Then the heel goes down. During this process, the weight of the body is at first on the front of the feet, then moves to the heel. Lieberman and his colleagues saw this motion firsthand in Kenya — the runners landed on the fronts of their feet.

When a person wears shoes, however, he tends to run so that his heels hit the ground first. The impact of the heel hitting the ground may be much more forceful than the impact of the front of the foot hitting the ground.

In the 1970s, shoe companies began selling running shoes that had cushioned soles. Those soles distributed the body weight through the foot and may have influenced the way people ran. Once runners started wearing these shoes, they could land on their heels and still be comfortable.

The researchers also studied barefoot runners in their laboratory in Boston. The goal was to measure the force with which a runner’s foot hits the ground. Force is calculated by multiplying the mass of an object — such as a human body — with its acceleration. By studying this force, the scientists could compare the impact of different running styles.

“A rear-foot strike is like someone hitting you on the foot with a hammer with about one and a half to three times your body weight. It would hurt without a shoe,” Lieberman told Science News. “A forefoot strike is like having no one hit you at all.”

Daniel Schmitt is an evolutionary anthropologist at Duke University. He told Science News that the new study by Lieberman and his colleagues is “really elegant and well done,” and that the finding is a clear, good example of the science behind different running styles.

Lieberman’s study explores the physics of running, which is a complex topic. Reed Ferber is a biochemist at the University of Calgary in Canada. The idea that barefoot running is better “is a massive assumption,” he told Science News. “Fundamentally, there are no studies out there that show barefoot running is less injurious.” In other words, don’t throw out those fancy running shoes just yet.

POWER WORDS (adapted from Yahoo! Kids Dictionary)

biological evolution The process of physical change in living things across generations.

biology The science of life and of living organisms, including their structure, function, growth, origin, evolution and distribution.

biochemistry The study of the chemical substances and vital processes occurring in living organisms.

force The capacity to do work or cause physical change.

The spider “almost fell right on me,” says Autumn, who was lying in bed at the time. “I was terrified.”

Once he got over his fear, Autumn started to think about what he had seen. How did both creatures manage to defy gravity and walk on ceilings? And why was the gecko so much stickier than the spider?

A gecko has feet that can grip glass, even when the gecko is upside down.

K. Autumn

Autumn happened to be a gecko expert, based at Lewis & Clark College in Portland, Ore. So, when he came home from Hawaii, he turned his attention to the gravity-defying feats of the little lizard-like creatures.

Six years later, Autumn and his coworkers think they’ve cracked the secret of how geckos stick to surfaces, no matter how smooth. Their work contributes to a growing list of discoveries about spiders, frogs, flies, and other sticky wall-crawlers.

Together, the research could inspire a new generation of super-sticky materials, with applications from medicine to engineering. Some day, you might even use “gecko tape” to walk up walls.

A sticky mystery

People have been fascinated by geckos for thousands of years. In ancient Greece, the philosopher Aristotle wondered how the reptiles could walk upside down. No one had a good answer for him.

Even when scientists got into the act in the last 150 years, they still had trouble cracking the gecko’s secret. Step by step, however, they did manage to narrow down the possibilities.

Originally, some scientists thought that geckos might make a kind of glue to coat their feet. Many insects produce a gooey ooze that allows them to stick to waxy leaves. But geckos don’t leave sticky tracks, so this theory couldn’t be right.

In 1939, a German scientist showed that geckos can stick to glass even when all the air has been sucked out. This finding disproved the idea that the animals might have suction cups on their feet.

Likewise, water doesn’t affect a gecko’s stickiness, which nixes the suggestion that a type of static electricity enhances its grip. Static electricity, which works best under dry conditions, is the kind of force that allows a rubbed balloon to stick to a wall.

The first significant clue came just a few years ago. Geckos have millions of microscopic hairs, or setae, on the bottom of their feet. Autumn’s group used a special microscope to take a closer look at a single hair. “Each hair had a really bad case of split ends,” Autumn says. In fact, a single hair could have hundreds of bristles.

A single hair, or seta, on a gecko’s foot splits into hundreds of tiny bristles, or spatulae.

K. Autumn, E. Florance

The researchers suspected that these hairs might be the key. They used special sensors and microtweezers to analyze the setae, one at a time. Their work revealed a few surprises.

First of all, the hairs aren’t sticky by themselves. “We tried for months,” Autumn says. But “we couldn’t get them to stick until we measured how the gecko really moves its feet and toes. The secret is mechanical.”

Simply pushing the setae onto the surface and dragging them forward a tiny bit makes them stick, the researchers found. Just increasing the angle at which a hair touches a surface then allows the hair to pop off. In effect, a gecko peels off its feet just as you would peel off adhesive tape.

It’s really the size and shape of the tips of gecko foot hairs that matter most. At the right angle and pressure, a single hair can lift the weight of a large ant. A whole gecko’s worth of setae could lift the weight of a child.

Ceiling walkers

Autumn has focused on geckos partly because they are the biggest type of animal that can walk on ceilings. Some of the 850 species of geckos can grow to be as big as iguanas.

Other scientists are taking a broader approach. Around the world, teams of biologists, chemists, physicists, and engineers are using different strategies to understand how a variety of animals might stick to slippery things.

One group in Germany, for example, recently looked at setae in many different creatures that varied in size, from beetles and flies to geckos and spiders. The heavier the animal is, they found, the smaller are its hairs. A beetle’s hairs, for instance, are about a tenth the width of a human hair. A gecko’s hairs are one-fiftieth the size.

“Spider-Man would need hairs that are another factor of 10 to 20 smaller than the gecko’s,” says Ralph Spolenak, a materials scientist from the Max Planck Institute for Metals Research in Germany, who participated in the research. “This is much smaller than anything found in nature so far. So, it’s very unlikely that you will happen to run into Spider-Man down the hallway.”

However, scientists could develop materials that copy what gecko hairs do.

That’s exactly what Autumn and his colleagues have done. To test their theory about gecko adhesion, the researchers designed several types of “gecko tape.” So far, the resulting tape has been sticky, but not nearly as sticky as geckos are on their own.

Researchers continue to work towards making better versions of gecko-inspired tape, with plenty of exciting applications in mind. Think: ouch-less Band-Aids, robots that can climb walls, delicate surgery on one blood vessel at a time, and more.

Eventually, after a lot more work by scientists and engineers, you might even be able put on a pair of gecko gloves and gecko socks and hang out on the ceiling for a while.

“I imagine every one of you has at least once dreamt of being Spider-Man, looking at things from a different perspective, not being subject to everyone else’s constraints,” Spolenak says. “Just being Spider-Man for a while would definitely be very cool.”

“Forget Spider-Man,” Autumn says. “Think Gecko-Girl instead.”

His 7-year-old daughter, Kendra, has already asked to be first in line. Who wants to be number two?

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From that point on, the intense highs and lows of long-distance running consumed me. During some stretches, I thought I might just crumple to the ground. Then, inspired by the roaring crowd, my stride would suddenly feel strong and smooth. My body would become a machine, light as a feather.

A Boston crowd watching the running of a marathon.

Hans Kieserman

The joy of completing my second marathon carried me across the finish line 3 hours, 40 minutes, and 16 seconds after I had begun. Agony immediately took over. I couldn’t walk properly for days.

All of the excitement over the New York City marathon, run 6 months after Boston on Nov. 2, inspired a new wave of marathon fever in me. I’ve already talked with a few friends about running it together next year. At the same time, I have mixed feelings about how much more my body can take. I just ran my third marathon a month ago. Now, I can’t run a step, due to a deeply cracked shin bone that is also keeping me from doing many of the other things I love, like climbing, biking, even walking and yoga.

A distance of 26.2 miles is just a long way to run, says Seth Kinley, an athletic trainer at Pennsylvania State University in University Park, Penn. “The bottom of your foot strikes the ground thousands of times.”

In labs across the country, researchers are using high-tech equipment to design new kinds of gear and improve training routines. By addressing nagging pains and other problems, sneaker science is helping athletes go faster, stronger, and longer.

Designing better gear

To combat the stresses inflicted by running and other sports, scientists study how the body moves. They then search for ways to help it move better.

Improvements often happen in baby steps. It can take as long as 2 years to turn an idea into a shoe that you can buy in a store, says Gordon Valiant, a biomechanist at Nike headquarters in Beaverton, Ore.

The process begins when an athlete or employee points out a specific need. Some athletes might want a shoe that prevents knee injuries. Others might wish to sprint faster or get a quicker start. Still others might want a shoe that works well on mountain trails.

Experiments come next. At the Nike Sports Research Lab in Beaverton, basketball courts, treadmills, and padded running platforms have sensors that measure the forces of impact. Wind tunnels and temperature-controlled chambers simulate real-world conditions. High-speed cameras take a thousand or more pictures per second. Computers perform analyses. Athletes come in to run and jump. A team of more than 25 experts watches their every move.

“We spend a lot of time in the lab measuring the different forces acting on the lower extremities and feet of athletes,” Valiant says. “That gives us insight into how we can either enhance or not interfere with the athlete’s motion, while at the same time protecting them from forces, or allowing them to use forces to their advantage. Knowledge of those things can really be applied to innovative designs.”

Adidas, New Balance, Reebok, and other companies conduct their own research, all with the same goal—to make better, faster, cooler-looking shoes. Of course, profits are important, too. Sneakers, as you may know, can cost a lot of money, and the market is extremely competitive. Research is also going on at universities, sometimes for commercial reasons, other times to help coaches and athletes train better, or simply for the scientific interest of the work.

Basic movements

The basic movement of a runner’s foot is fairly simple. The heel strikes the ground first, followed by a roll inward toward the toes. Then, the foot goes rigid, which allows the runner to launch forward, in a springboard kind of way. Any slight variation in that ideal running form can end up causing all sorts of injuries.

Using the right sort of footwear—whether running a marathon or just jogging—can reduce the chances of suffering painful injuries.

“Pain in the knees, hips, and back can all stem from what’s going on in the foot,” says Kinley, who has worked with runners at Penn State for 10 years.

Everyone’s feet are different, though there are some general categories based on the shape of the arch. I have slightly flat feet, which makes my legs roll inward and throws my stride off kilter. I used to have severe knee pain as a result, until I started wearing stable shoes with lots of support.

Each shoe and piece of clothing is designed and tested to meet specific needs, Valiant says.

Marathon runners want lightweight footwear with plenty of cushioning, for example. Racing shoes for shorter distances often sacrifice cushioning for flexibility. Basketball shoes need to be sturdy enough to deal with lots of twisting and jumping.

Moreover, the best combination of shoe length and width varies from men to women to kids, and among people from different ethnic backgrounds.

With so many choices, it’s important to make sure you don’t get sucked in by the latest styles, Kinley says. “Just because it’s fancier looking or has cool colors or costs a lot,” he says, “doesn’t mean it’s a better shoe to have.”

Marathon tips

Hoping to avoid some of the pain of my first marathon, which I had run months before in Minnesota, I went looking for tips at the Nike store in Boston the day before this year’s race. There, I met Mark Riley, business director for men’s running footwear. He had traveled from Nike headquarters to run his 12th Boston marathon.

Near the finish line of the Boston marathon.

Hans Kieserman

Mark showed me some of Nike’s newest products. He didn’t seem to mind that I was wearing New Balance shoes. Then, talk turned to race-day strategies.

“Don’t start out too fast,” Mark warned me over and over. The biggest hills come late in the race, he said, and you want to make sure you have enough energy left to charge up the slopes. “Trust your training,” he added. “You’ll do great.”

Of course, when it comes to running marathons, anything can happen. On April 21, 2003, in Boston, temperatures soared to 75 degrees under a fierce sun. A strong head wind blew for the last 10 miles of the race.

When I finally reached the end, I realized that no amount of sneaker science could have kept my feet from aching, along with my legs, back, lungs, and everything else. When it comes to a marathon, shoes do matter. But determination matters more.

Going Deeper:

Additional Information

News Detective: Emily runs a marathon

Scientist’s Notebook: Sneaker Scientists

Word Find: Sneaker Science

Questions about the Article