Evolutionary biologist Daniel E. Lieberman caused an international uproar nearly a decade ago when he published a paper showing that running in cushioned shoes encourages people to hit the ground harder than when running barefoot. Lieberman, a professor of biology at Harvard University, also began running barefoot and continued to do so because he enjoyed it. Every spring after running the Boston Marathon, he bought his traditional shoes, at least for a pair of shoes or not at all. The more he walked barefoot, the more restless and secure his feet became. But I can still feel the earth when my classes were very thin, says Lieberman.
Now Lieberman and his colleagues have conducted another study at Harvard as well as in Germany and Kenya, published Wednesday in Nature, that confirms his suspicions. This suggests that although the calluses become thicker when people frequently go barefoot, this extra protection does not make them feel inferior. Basically, the hard surface of the cornea transmits the mechanical force through the foot to the deeper nerves in the skin.
Lieberman and his colleagues measured the sole's sensitivity to mechanical stimulus and showed that overweight people were just as sensitive to vibration as people with thin or no tartar. Researchers compared calluses and foot sensitivity in 81 people from western Kenya, some of whom regularly walked without shoes and others who did not. They collected similar data from 22 people in Boston.
Lieberman says that with cushioned shoes, the stiffness of the sole slows the speed at which the body hits the ground, making the effect more comfortable, but the force is the same. The energy hitting your leg is three times greater than in padded shoes when you run barefoot, he says. He says it's theoretically possible that this additional effect is responsible for the doubling of knee arthritis rates since World War II. However, there is no concrete evidence of such a relationship.
In some ways, Lieberman says, walking barefoot is better for the body than wearing deep-soled shoes. But he insists it's not anti-shoes: I'm not saying people shouldn't wear shoes. Rather, he believes that scientists still don't understand the effects of shoes on the body during millions of steps. Lieberman says it would be difficult to study the effects of wearing millions of shoes on millions of feet in humans over a period of more than 70 years, but he is currently researching the effects of such cushions on animal movement.
Balance can also be a disadvantage of soft soles. As you get older, your feet become less sensitive. Even if they lose contact with the ground, they may be at higher risk of falling, says Lieberman. According to one study, gymnasts and martial artists go barefoot to improve their connection to the ground, and Formula 1 racers wear hard-soled shoes that actually increase their sensitivity. Healthy walking. Studies like Lieberman can lead to better-designed shoes that complement the body's natural capabilities rather than weakening them.
