Background. Few studies of physical activity in patients with anorexia nervosa (AN) have included a suitable control group. Nor has such research considered the influence of parents' activity on that of their children. Our first prediction was that adolescents with AN would be significantly more active than healthy controls both prior to, and during, the progression of their disorder. We also expected that the activity levels of parents and their daughters would be correlated, and that this relationship would be stronger in patient than control families. Finally, we expected that the AN parents would be more active and report a greater commitment to exercise than the control parents.

Method. In a case-control design, we employed multiple indicators of physical activity from adolescent females and their parents, using longitudinal, retrospective, self-report measurements.

Results. AN patients were significantly more active than controls both during the course of their disorder and prior to its onset. Parents' activity related to their daughter's activity, but this relationship was not stronger in the parents of the patients.

Conclusions. Future research is needed to determine whether the relationship between parents' and children's activity levels reflects environmental or genetic influences, or a combination of both factors. The important observation of a significant increase in patients' activity levels at least a year prior to diagnosis of the disorder suggests that enhanced physical activity may play a role in the development of the disorder. This may also serve as an early warning sign of a subclinical eating disorder in adolescent girls.