On a normal diet the body is able to store between 1500-2000 calories in the form of glycogen and roughly 75% of this glycogen is stored within the muscle. During prolonged exercise glycogen is broken down into glucose which then is ready for the muscles to use as a source of energy production. If an athlete is training heavily, their glycogen will deplete faster than it can be replaced and will cause the athlete to feel fatigued which will effect their performance by lowering their capability to maintain the exercise being performed. Athletes who are performing in an event that will last for more then 90 minutes will increase their carbohydrate intake by about 70% about 5 to 6 days prior to the event.