Physical exercise has a positive effect on physical and mental health. However, the amount of exercise can also become too much at which point the adverse effects predominate. Moreover, excessive exercise can lead to compulsive behavior and dependence. The purpose of this paper is to investigate exercise as a possible primary addiction and answer the question why it is rarely qualified as such. The results indicate that insights from various disciplines are required in order to obtain a full understanding of this issue. From a physiological perspective, several hypotheses have been proposed in an attempt to explain the mechanism of exercise addiction. However, each of the contemporary theories requires further testing as none of them have been proved conclusively. In turn, the same is true from a psychological viewpoint, as consensus in this field on the nature of exercise addiction is still to be established, despite the existence of multiple theories. When taking a behaviorist approach, motive of an addicted exerciser is important to consider and it can be explained through both reinforcement and punishment. Lastly, even though it is highly associated with eating disorders, exercise addiction can also occur independently as the primary dysfunction. In conclusion, compulsive and excessive exercise can be qualified as a behavioral addiction. However, this phenomenon requires further attention to become a treatable condition.