Recall a time when you took a long walk on a beach. Your feet probably felt pretty tired by the end of it. “Your feet are tired because every time you press down on sand, the sand moves away from you, so your foot muscles have to work harder than on stiff surfaces,” says Daniel Lieberman, chair of the Department of Human Evolutionary Biology at Harvard University.
The difference between walking on shifty sand or hard cement is comparable to the difference between walking barefoot or in shoes. “When you walk in shoes, your feet are pressing against a stiff substitute for the ground that makes the muscles in the feet have to work less than if you were barefoot,” he says.
While less work may seem like a good thing, it may actually leave your feet vulnerable to injury.