The purpose of these studies is to use patients with McCardle's disease as "an experiment in nature" to study the various factors which regulate muscle blood flow during exercise. Patients with McCardle's disease have excessive steadly-state blood flow responses to exercise, but little is known about the time course of these responses. The question we hope to address with these individuals is what mechanisms cause the initial rise in blood flow after a single contraction or several brief contractions is. The current concept is that the muscle pump (mechanical interactions between the blood vessels and the contracting muscles) are responsible for almost all of the initial rise in flow after a single contraction. If this is the case, then the patients with McCardle's disease should have an identical response to normal subjects. However, if metabolites contribute to this early rise in flow we expect to see an augmented response in the patients with McCardle's disease.