Defects in glycolysis can lead to muscle weakness, but they do not typically cause hyperglycemia, as seen in this patient.

Urea cycle disorders can cause symptoms related to ammonia buildup, such as lethargy and poor appetite, but they do not primarily affect muscle strength or cause hyperglycemia.

The patient's symptoms are suggestive of a glycogen storage disease, most likely McArdle disease (glycogen storage disease type V). This disease is caused by a deficiency in the enzyme myophosphorylase, which is necessary for glycogenolysis in muscle cells. The inability to break down glycogen in muscle cells results in energy shortage in muscles, leading to muscle weakness and fatigue.

Defects in the Cori cycle could cause muscle weakness due to decreased lactate recycling, but would not typically cause hyperglycemia.