Figure 12. Control of glycogen synthesis in muscle.

Both insulin and exercise increase glucose uptake via GLUT4. Increased glucose 6-phosphate (Glc-6-P) levels provide feedforward activation of GS (glycogen synthase). Insulin also causes dephosphorylation and activation of glycogen synthase by promoting the inactivation of GSK3 by Akt. The effect of exercise on glycogen synthase phosphorylation is more complex, potentially dephosphorylating via a PP1G containing R_GL and well as increasing phosphorylation via activation of protein kinases such as AMPK. PhK, phosphorylase kinase.