Muscle glycogen
The storage form of glucose in muscle, serving as an immediately available energy reserve for physical effort, distinct from liver glycogen.
Glycogen is the storage form of glucose. There are two reserves: liver glycogen (in the liver, about 100 g, which maintains blood glucose) and muscle glycogen (about 400 g, reserved for the muscle’s own use).
An original angle (muscle is selfish): a little-known peculiarity: muscle glycogen CANNOT be released back into the blood for other organs. Muscles lack the necessary enzyme (glucose-6-phosphatase). In other words, the muscle “jealously guards” its glycogen for itself. Only the liver can “share” its glycogen with the rest of the body.
This has implications for sport: muscle glycogen is the preferred fuel for intense efforts. When it runs out (after about 90 minutes of sustained effort), you meet the famous marathon “wall“: performance drops abruptly.
Carb loading: endurance athletes “load” up on carbohydrates before a competition to maximise their stores. After exercise, resynthesis is fastest in the first 30 to 60 minutes (the only real “window” that counts, especially for people doing repeated efforts).
Each gram of glycogen is stored with about 3 g of water. This is why going back to carbohydrates after a low-carb diet makes you “swell back up” (glycogen-related water retention): a rise on the scales that is NOT fat, just water stored with the glycogen. Understanding this avoids post-diet panic.