Why does glucagon cause glycogenolysis in muscles?

Unlike the liver, glucagon does not directly cause glycogenolysis in muscles. Muscle cells do not express the glucagon receptor, so glucagon has no direct effect on glycogen breakdown in muscles. However, during exercise or stress, epinephrine (another hormone) stimulates glycogenolysis in muscle cells. Epinephrine activates a similar signaling pathway involving cAMP, leading to the activation of glycogen phosphorylase, which breaks down glycogen into glucose-6-phosphate. This glucose-6-phosphate is used in glycolysis to generate ATP for muscle contraction.