In this part the author discussen the different explanations and reflections about hyperactivity in anorexia nervosa. Although this aspect has been neglected in several studies, one has tried to elucidate this phenomenon from differing theoretical models. Beside a number of speculations difficult to systematize, the author divided the other considerations according to the main point of view: from a phenomeno-anthropologic, psychoanalytic, behavioristic or biologie perspective. The various ways of explanation are critically discussed and eventually completed by own opinions or suggestions for further research. Finally the significance of hyperactivity in the total therapeutic approach of anorexia nervosa is explained. An extensive bibliography on this subject is added.