Changes

Glycogen is the critical fuel supply for endurance running. * Glycogen is formed primarily from the carbohydrates we consume and is stored in our livers and muscles. * The glycogen in our livers can leave the liver and flow via our blood to our muscles, brains and other organs. * The human liver typically stores between 90 and 160 grams of Glycogen, or 350 to 650 Calories. * Blood typically contains less than 20 calories of glucose. * The glycogen in our muscles can only be used by those muscle fibers. * Glycogen can also be created from protein via a process called [http://en.wikipedia.org/wiki/Gluconeogenesis gluconeogenesis], but not from fat.