The Exercise Test

Abstract

A “semi-ischemic” forearm exercise test is useful for screening patients with muscle enzyme defects in the metabolic pathway from glycogen (glucose) to lactate. McArdle [1] first described the “ischemic” forearm exercise test; he observed no rise in plasma lactate concentration in the original patient. The test was later modified [2] and has since been used to screen patients with McArdle’s disease (glycogenosis type V). This test, in which the exercising arm is maintained at conditions of complete ischemia, is also available as a diagnostic test for other types of glycogenosis, including types VII [3] and III [4]. However, patients with type V glycogen storage disease (GSD) developed myoglobinemia, massive myoglobinuria, and marked serum creatine kinase elevation subsequent to routinely ischemic forearm exercise tests. Substantial evidence has been accumulated that the ischemic forearm exercise test is potentially hazardous to type V patients, as it might induce massive myoglobinuria sufficient to result in acute myoglobinuric renal failure [5, 6]. Therefore, the test had to be modified in the following fashion [7, 8]: after 30 min rest, blood is drawn from the antecubital vein of the nonexercising arm. A small size sphygmomanometer cuff applied around the wrist of the exercising arm is inflated to 200 mmHg. A second standard cuff around the upper arm is then inflated to mean arterial pressure, and the patient squeezes a hand manometer as powerfully as possible 120 times during a period of 2 min. Immediately after the exercise, the second cuff is rapidly inflated to 200 mmHg. Blood is drawn with a butterfly needle from the antecubital vein of the exercising arm 2 min after the end of the exercise, and the cuff around the upper arm is released. Then blood is obtained every 1 or 2 min four to five times (Table 1). This semi-ischemic forearm exercise test has been used for many patients with types V, VII, and III GSD, including cases of our own, and no severe signs or symptoms appeared during or after the test.