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.