"If you do make this change, do so slowly and carefully," warns Paul DeVita, PhD, who studies biomechanics at East Carolina University.

Your legs and feet move differently when you run barefoot. This can make you more efficient. But the unfamiliar movements can strain your muscles and tendons.

June 1, 2012 (San Francisco) -- You may be able to run faster if you take off your shoes. But you also risk injury, new studies show.

Barefoot Running Picking Up Speed

Barefoot running is becoming increasingly popular. Advocates say it is more natural. And many shoe companies are making "minimalist" footwear that is lighter and less restrictive.

Researchers are investigating these claims. They presented a dozen studies at the Annual Meeting of the American College of Sports Medicine now being held here.

In one study, 12 people ran on a treadmill for six minutes barefoot and for six minutes with shoes. They got plenty of rest in between.

The runners did not breathe as hard when they were barefoot. Their male runners' hearts did not beat as fast (although the female runners' hearts beat faster.) And they didn't feel as tired.

Joel R. De Paoli, MS, led this experiment when he was an exercise physiologist at San Francisco State University. He tells WebMD that runners may move less efficiently when they wear shoes because their heels strike the ground first. That blocks their movement forward.

"There is a likelihood that you land more on the forefoot when you run barefoot," he says.

In another study at Adrian College in Adrian, Mich., competitive runners tried Vibram Five Finger Bikilas shoes. These shoes resemble gloves for feet. They are supposed to simulate running barefoot while providing some protection.

The runners ran a mile in 7.17 minutes wearing the Vibram Five Finger shoes, but 7.36 minutes wearing traditional running shoes. The researchers calculated that the weight of the shoe only accounted for 18% of the difference in speed.