McArdle disease

Since glycogen cannot be broken down into glucose-1-phosphate via the enzyme myophospho-rylase, glucose molecules as a source of energy flowing through the blood will be very limited, especially during modest exercise. Recall that glucose-1-phosphate is converted to glucose-6-phosphate and subsequently into glucose. Glucose is then used to produce ATP via glycolysis. Under anaerobic conditions, however, pyruvate is converted into lactate. Since there is an insufficient level of glucose, there will be an insufficient level of pyruvate produced and also lactate. Therefore, in McArdle disease, the lactate concentration does not increase during exercise.