analysis of excessive running in the development of activity anorexia. PHYSIOL BEHAV 58(3) 451-457, 1995.--Food restriction combined with activity wheel access produces activity anorexia: a combination of excessive running, reduced food intake and rapid weight loss. Temporal distributions of running in activity anorexia were examined in a reversal design with one of 2 × 2 × 2 factorial combinations (pelleted-vs-powdered food × deprivation × wheel access) as the treatment condition. Wheel revolutions were recorded in 30 min intervals; body weights, food and water intakes were measured daily. Only wheel access combined with food deprivation reliably produced activity anorexia. Excessive running occurred in the absence of schedule-induced polydipsia, was unaffected by food form, and showed distributional characteristics of facultative behavior. These results are inconsistent with schedule-induced behavior explanations. Running distributions appeared consistent with chronobiological models with light/dark onset and feeding serving as zeitgebers. Activity anorexia Activity Temporal running distribution Food deprivationSchedule-induced behavior Rats RATS (8,13,20,21), mice (8), and golden hamsters (4,5) allowed access to running wheels combined with food deprivation schedules (60-90 min daily food access), ran excessively, ate little and eventually starved. The phenomenon, labelled activity anorexia (7), is characterized by dramatic increases in activity paradoxically associated with decreased food consumption, and has also been observed in some humans diagnosed with anorexia nervosa (10,15,27) as well as some athletes (14,23,26,28). These observations have led researchers (7,9) to suggest that activity anorexia, induced experimentally in rodents, might serve as a useful model for the understanding of anorexia nervosa and its treatment in humans. Consistent with this notion, Epling and Pierce (7) also observed dramatic increases in running immediately before and after scheduled feeding. They suggested that the running might be a schedule-induced behavior. If water is continuously available during a variable interval schedule of food reinforcement, rats become polydipsic, drinking several times their normal daily water intake (11). The behavior typically manifests itself as an interim schedule-induced behavior, as described by Staddon (24), and has also been obtained with fixed time schedules of reinforcement [e.g., (25)]. If one were to postulate water availability as somewhat analogous to availability of a running wheel, then one could also postulate the excessive wheel running as scheduleinduced under the same conditions that produce schedule-induced polydipsia (17,25). Although studies of schedule-induced behavior have utilized small food portions as reinforcers and brief (commonly 1 min) periodic schedules, at least by analogy, activity anorexia might be a special case of schedule-induced behavior, or the behaviors might share common underlying mechanisms. If true, variables influencing schedule-induced behavior...