A nagging pain in the top of your foot or the front of your shin that's worse when you exercise, but present even at rest. It's impervious to ibuprofen and acetaminophen.
The condition: It's probably a stress fracture. Bones, like all the other tissues in your body, are continually regenerating themselves.
"But if you're training so hard that the bone doesn't get a chance to heal itself, a stress fracture can develop," explains Andrew Feldman, M.D., the team physician for the New York Rangers. Eventually, the bone can be permanently weakened.
The diagnostics: Radioactive dye reveals the fracture in the x-ray, and you'll be told to stop all running until the crack heals. Worst case, you'll be in a cast for a few weeks.