"Few studies are carried out in order to estimate the prevalence of high level exercise in the eating disorders. Davis et al. have achieved a prevalence study. The results indicate that a large majority of patients with anorexia nervosa (80,8%) were exercising excessively during an acute phase of the disorder. Research on animals, specially on rats, brings us an interesting model explaining interactions between anorexia nervosa and hyperactivity. With animal models, we have noticed that, when rats with access to a running wheel, are restricted in their food intake, they become excessively active, and paradoxically reduce food consumption. Many searchers have tried to explain this phenomenon. Morse et al. have pointed from animal models that the level of hyperactivity was linked to the severity of food restriction. This result can be explained by a failure of a part of the brain involved in rest and activity regulation. Animal research brings us explanations about the effects of starvation on the endocrine system and the neurotransmitters. Broocks et al. have shown that corticosterone concentration in plasma was synergistically increased by semi starvation and exercise, and the reduction of triiodothyronine by semi starvation was significantly greater in the running wheel group. An other study of Broocks et al. has revealed an increased hypothalamic serotonin metabolism with the combined effect of hyperactivity and food restriction. Tryptophan, an amid acid involved in serotonin synthesis, can also play a role in the maintenance of anorexia nervosa. In starvation conditions, opioid releasing caused by physical exercise would decrease food intake. Exner's study and Adan's one have shown that leptin would be involved in semi starvation induced hyperactivity mechanisms. In spite of animal models can not be entirely generalized to human, they are useful to try to explain biological supports of hyperactivity. Hyperactivity is not only a strategy to lose weight, but also a specific symptom which completes the clinical triad. Animal studies have led to promising results; we might use medicine, such as serotonin reuptake inhibitors or opioid antagonists in the treatment of hyperactivity in anorexia nervosa."