The regulation mechanism involves:
a) The hormones catecholamines (epinephrine, norepinephrine) and glucagon cause the increase in CAMP levels in cells. This CAMP activates protein kinase, which stimulates the key enzyme phosphorylase for glycogenolysis. Briefly, phosphorylase b is phosphorylated, and rendered highly active, by phosphorylase kinase.
b) Immediately after the onset of muscle contraction, glycogenolysis is highly increased in muscle by the rapid activation of phosphorylase due to the activation of phosphorylase kinase by Ca++ ions.