An unhealthy reliance on exercise for daily functioning. The exercise often becomes the main mechanism for coping with everyday stresses. Exercise addiction is characterized by dependence (a belief that exercise is essential for feeling good), tolerance (the need to progressively increase the level of exercise in order to achieve the same level of feeling good), and withdrawal (unpleasant feelings, such as tiredness and irritability, associated with stopping or reducing exercise levels). The cause of exercise addiction is not known, although tentative links have been made with release of endorphins during exercise. In many cases, exercise addiction is associated with an underlying problem, such as career or family stress. Treatment is notoriously difficult (some exercise addicts will not stop no matter what enticements or warnings you offer them), but it may be successful if the underlying problem causing it is identified and remedied. Continued exercise addiction can lead to overuse injuries, and social, family, and career problems. Running is the most common sport associated with exercise addiction.