Anorexia nervosa is a complex psychiatric disorder that can lead to specific somatic complications. Malnutrition is frequent and can involve a decrease of mobility, up to functional impotence, in individuals with extremely severe cases. The aim of this pilot study was to examine muscle strength and peak expiratory flow (PEF) in severely undernourished patients with anorexia nervosa at admission and after 5 wk of renutrition by tube feeding, and to find the clinical and biological correlates of muscle-strength impairment.