Here is a thoughtful and worthy essay, from Nautilus, about exercise addiction. The topic certainly deserves attention. However, as a skeptic of lumping strong habits under the rubric of addiction, I was not convinced by this author that the phenomenon is accurately described by the term (as opposed to compulsion, another term brought up here). She acknowledges that no agreed-upon definition of exercise addiction exists but pushes on without trying to convince us that people who work out too much are in fact addicts. Are people who study too much addicts? Who worry too much? Who are neat freaks? Is the definition of addiction simply overdoing it?
Still, making the connection between eating disorders and exercise addiction seems to me astute and cries out for of more study.