Changes

Running requires energy, and that energy comes from a mixture of carbohydrate, fat and [[Protein]]. The supply of fat is practically unlimited, but there is a limited supply of carbohydrate. This carbohydrate is stored as [[Glycogen]] in the liver and muscles. The liver [[Glycogen]] can travel via the blood to any of the muscles as well as the brain, but [[Muscle|muscle ]] [[Glycogen]] cannot leave the muscle fibers. Typically, there is sufficient [[Glycogen]] for about 20 miles of running at marathon pace, making the final stages of the marathon tough. Carbohydrate loading increases the [[Glycogen]] stores beyond their normal levels.