Your butt may be more important to your running than you realize.

New York Times writer Jen Miller has been told she suffers from “dead butt syndrome.” Medically speaking, this is a condition called gluteus medius tendinosis, which is an inflammation in one of the tendons that make up the gluteus medius. The gluteus medius is one of three muscles that comprise the buttocks.

According to Miller, this condition is a “very isolated and painful injury.” It knocked her out of marathon training and she notes it was due primarily from running too much and cross training too little.

Apparently, the condition is common with runners and doctors are just beginning to understand it and its symptoms.

“In the last five to 10 years, we’ve just realized how much of an important role the gluteus medius plays in stabilizing the hips and the pelvis in running,” says Dr. Darrin Bright, a sports medicine physician with Riverside Methodist Hospital in Columbus, Ohio. “For people who have persistent pain, it’s healing gone wrong…That gluteus medius isn’t firing the way it’s supposed to. You’re getting an inhibition of the muscle fibers. It’s kind of dead.”

For More: New York Times