A pattern of compulsive, excessive exercise driven by preoccupation with leanness and performance, often occurring alongside or instead of the food restriction of anorexia nervosa. Affected athletes train through injury, illness, and exhaustion, experiencing intense guilt when unable to exercise, and may combine the overtraining with restrictive eating to maintain an unnaturally low body weight. It appears across endurance sports, aesthetic sports, and weight-class competitions where leanness is prized. The health consequences include stress fractures, hormonal disruption, cardiac strain, and the psychological toll of an identity fused to exercise. Treatment addresses both the compulsive behavior and the underlying body-image and anxiety issues, often requiring the athlete to step away from sport temporarily. Coaches play a crucial role in early recognition.