Regulation of skeletal muscle glycogenolysis during exercise.
Muscle-glycogen breakdown during exercise is influenced by both local and systemic factors. Contractions per se increase glycogenolysis via a calcium-induced, transient increase in the activity of phosphorylase a, and probably also via increased concentrations of Pi. In fast-twitch muscle, increases in the AMP and IMP levels may increase phosphorylase activity. The rate of muscle-glycogen breakdown during exercise depends on the pre-exercise glycogen concentration and is also influenced by hormones. Insulin may inhibit glycogen breakdown, whereas epinephrine enhances the rate of glycogen use in contracting muscle by increasing the phosphorylase a activity via increased cyclic AMP production. The availability of blood-borne substrates may also influence muscle glycogenolysis and, therefore, exercise performance.
Hargreaves
M
M
August Krogh Institute University of Copenhagen, Denmark.
Richter
E A
EA
D001786:Blood Glucose / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D004837:Epinephrine / Q000502:physiology; D015444:Exercise; D006003:Glycogen / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000502:physiology; D009132:Muscles / Q000378:metabolism*; D006005:Phosphorylases / Q000378:metabolism
D001786:Blood Glucose; D007328:Insulin; D006003:Glycogen; D006005:Phosphorylases; D002118:Calcium; D004837:Epinephrine