Contracture in McArdle's Disease

IN 1951, McArdle¹described a patient whose major symptom was limitation of vigorous activity because of cramps after exercise. When electromyographic examination was performed during a cramp, electrical silence was found despite maximum shortening of the affected muscle; this could be considered a contracture (shortening of muscle without propagated action potential²). McArdle recognized the similarity of this event to the classical experiments of Lundsgaard³in which muscle poisoned by iodoacetate was able to contract without formation of lactic acid. When the patient exercised forearm muscles under ischemic conditions, in contrast to a normal person, there was no rise in venous lactic acid. McArdle therefore postulated that the disorder was due to a defeat of muscle glycogen breakdown. The nature of the enzymatic abnormality was clearly established by Schmid and his colleagues in one family,⁴and by Pearson, Mommaerts, and their colleagues in another.⁵Inability