The principal stored form of carbohydrate energy (glucose), which is reserved in muscles. When a weightlifter's muscles are full of glycogen, they look and feel full.

a type of starch synthesized from glucose for intracellular storage. The primary glycogen stores are in the liver and in the muscles; liver glycogen stores will be broken down to glucose and released into the bloodstream when blood sugar levels are low, whereas this does not happen with muscle glycogen stores which will be used only to provide fuel for the muscles themselves. Note that way that glycogen is stored in the body requires four grams of water to be stored for each gram of glycogen. The combined weight and volume of muscle glycogen stores accounts for a significant part of total muscular size. The depletion of these glycogen stores (and the release of the accompanying water) is what accounts for the rapid weight loss experienced in the first few days of ketogenic and other reduced-carbohydrate diets.