Exercise intolerance in a thin 17 year-old is from anorexia?

Likely The Cause. Patients suffering from anorexia nervosa restrict their intake leading to protein-energy malnutrition. This in turn causes muscle dysfunction and finally exercise intolerance. In one study all subjects showed impaired muscle function on strength and exercise measurement. 50% of patients showed nerve damage and tissue biopsies showed muscle damage at the microscopic level.