A 19-year-old man has early fatigue and muscle cramps while playing sports. He is fine when walking or doing light levels of work. On examination, he appears well and the muscle strength in the proximal muscles is normal. There is no muscle fatigue with repetitive arm grip exercises. After an exercise stress test, his serum creatine kinase (CK) is elevated and lactate level is normal. Which of the following is the most likely diagnosis?

There are many types of glycogen storage diseases, each caused by a different enzymatic abnormality. The best-known types of glycogen storage disease are those that have hepatic-hypoglycemic pathophysiology (e.g., von Gierke's disease) or those that have muscle energy pathophysiology (McArdle's disease). In McArdle's symptoms usually develop in adulthood, and it is marked by cramps and muscle injury with strenuous exercise, but not with usual activities. Gaucher's and Tay-Sachs disease are lysosomal storage diseases.