When Vibrams were first popular, I took to training with them on my runs. People told me to "take it easy" or you might get injured. I thought what's the worst that can happen? Well let me tell you. About a month into wearing them, I was doing a hard run and the trail had a section of concrete. My foot felt a sudden sharp pain and "snap!" I broke my 3rd metatarsal bone in my foot. Took a month or so to heal, and I decided to stop using the Vibrams.