[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Biochemistry](https://durgical.com/en/biochemistry/) › Exercise metabolism [Biochemistry](https://durgical.com/en/biochemistry/) · Topic # Exercise metabolism Muscle switches fuel with intensity and duration: phosphocreatine, glycogen with lactate, and then oxidised glucose and fat. Updated 2026-11-01 ## Key facts - First seconds: ATP and phosphocreatine (creatine kinase). Maximal effort up to 1–2 minutes: anaerobic glycolysis with lactate. - Prolonged moderate exercise: oxidation of glycogen, glucose and more and more fatty acids. - Contraction Ca²⁺ and AMP activate muscle glycogen phosphorylase; adrenaline adds to it through cAMP. - AMPK moves GLUT4 to the membrane during exercise without needing insulin. - Endurance training adds mitochondria, capillaries and capacity to oxidise fat. ## In detail - Phosphocreatine regenerates ATP instantly (creatine kinase) but runs out in about 10 seconds of maximal effort. - In a sprint, fast glycolysis makes pyruvate faster than mitochondria can use it: lactate leaves for the blood and the liver turns it back into glucose (Cori cycle). - As intensity rises, the share of carbohydrate oxidised rises; at moderate intensity and in long efforts fat contributes more (respiratory quotient 1.0 with carbohydrate and about 0.7 with fat). - During exercise insulin falls and glucagon, adrenaline, cortisol and GH rise: the liver delivers glucose and adipose tissue releases fatty acids. - AMPK, activated by falling ATP, inhibits acetyl-CoA carboxylase, lowers malonyl-CoA and lets fatty acids into the mitochondrion (CPT1). - Fatigue in long efforts coincides with muscle glycogen depletion; acidity and inorganic phosphate contribute in short, intense efforts. ## Clinical notes - McArdle disease: without muscle phosphorylase, cramps appear early in exercise with no lactate rise, and a 'second wind' comes when glucose and fatty acids arrive in the blood. - CPT2 deficiency causes muscle pain and dark urine (myoglobinuria) in long exercise or fasting. - Exercise improves insulin sensitivity and is a central part of type 2 diabetes care. - Creatine kinase rises in blood after hard exercise and far more in rhabdomyolysis. ## Pathways - [Glycolysis](https://durgical.com/en/biochemistry/pathways/glycolysis/) - [Glycogen metabolism](https://durgical.com/en/biochemistry/pathways/glycogen-metabolism/) - [Fatty acid β-oxidation](https://durgical.com/en/biochemistry/pathways/fatty-acid-oxidation/) - [Krebs cycle (citric acid cycle)](https://durgical.com/en/biochemistry/pathways/krebs-cycle/) - [Electron transport chain and oxidative phosphorylation](https://durgical.com/en/biochemistry/pathways/electron-transport-chain-and-oxidative-phosphorylation/) ## Related conditions - [McArdle disease (glycogen storage disease type V)](https://durgical.com/en/conditions/mcardle-disease/) - [Tarui disease (muscle phosphofructokinase deficiency)](https://durgical.com/en/conditions/tarui-disease/) - [Carnitine palmitoyltransferase II (CPT-II) deficiency](https://durgical.com/en/conditions/carnitine-palmitoyltransferase-ii-deficiency/) - [Type 2 diabetes mellitus](https://durgical.com/en/conditions/type-2-diabetes-mellitus/) - [Lactic acidosis](https://durgical.com/en/conditions/lactic-acidosis/) ## Related - [AMP-activated protein kinase (AMPK)](https://durgical.com/en/biochemistry/enzymes/amp-activated-protein-kinase/) - [Glycogen phosphorylase](https://durgical.com/en/biochemistry/enzymes/glycogen-phosphorylase/) - [Lactate](https://durgical.com/en/biochemistry/molecules/lactate/) - [Cori cycle](https://durgical.com/en/biochemistry/topics/cori-cycle/) - [ATP (adenosine triphosphate)](https://durgical.com/en/biochemistry/molecules/atp/) - [Adrenaline](https://durgical.com/en/biochemistry/molecules/adrenaline/) - [Fed, fasting and starvation states](https://durgical.com/en/biochemistry/topics/fed-fasting-and-starvation-states/) - [Insulin signalling](https://durgical.com/en/biochemistry/topics/insulin-signalling/) - [Carnitine shuttle](https://durgical.com/en/biochemistry/topics/carnitine-shuttle/) ## Test yourself Think of the answer, then tap the question to see it. ## Which system supplies energy in the first 10 seconds of maximal effort? Stored ATP and phosphocreatine, which creatine kinase uses to regenerate ATP. ## How does exercising muscle take up glucose when insulin is low? Contraction and AMPK move GLUT4 to the membrane through an insulin-independent route. ## Why does lactate not rise with exercise in McArdle disease? Because without muscle glycogen phosphorylase, glycogen is not broken down and does not feed glycolysis. ## Which respiratory quotient means mostly fat is being oxidised? A value near 0.7; pure carbohydrate gives 1.0. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/biochemistry/topics/exercise-metabolism/) Educational information, not medical advice. For any symptom, see a health professional. Sources: [Exercise and Physical Fitness: MedlinePlus](https://medlineplus.gov/exerciseandphysicalfitness.html) (MedlinePlus, US National Library of Medicine, 2026); [Physical activity](https://www.who.int/news-room/fact-sheets/detail/physical-activity) (World Health Organization, 2026); [PRKAA2: 5'-AMP-activated protein kinase catalytic subunit alpha-2 (human)](https://www.uniprot.org/uniprotkb/P54646/entry) (UniProt, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011). [← All of biochemistry](https://durgical.com/en/biochemistry/) ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/biochemistry/topics/exercise-metabolism/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/topics/exercise-metabolism/