There’s a good article on Over-Training Syndrome (OTS) at Outside Online: Running on Empty.

OTS is one of the scariest things I’ve ever seen in my 30 plus years of working with athletes,” says David Nieman, former vice president of the American College of Sports Medicine. “To watch someone go from that degree of proficiency to a shell of their former self is unbelievably painful and frustrating.”

Nieman, a professor of health and exercise science at Appalachian State University in North Carolina, has spent his career studying the effects of training on the immune system. In 1992, he received the first of a dozen distressingly similar letters from endurance athletes, each of them describing a sudden loss of ability as they struggled with everything from anemia to chronic dehydration to a basic inability to get out of bed. Nieman was both troubled and fascinated by these tales. Their symptoms all seemed to point to overtraining syndrome, and he’s been looking into the root causes of the condition ever since. [continue]