Rushall notes, 1990.

1. During exercise of any intensity or duration, more energy comes from fat than from carbohydrate oxidation. Increased fitness reduces the call for carbohydrate oxidation and, therefore, depletion of carbohydrate is stalled.

2. Preexercise diet affects performance. There is a suggestion that additional glycogen stored as a result of a high carbohydrate diet is burnt more rapidly than normally stored glycogen. At the end of a race, muscle glycogen levels are usually the same no matter what the pre-race dietary states. However, the extra energy from the hyper-stored carbohydrate would facilitate a more intense effort.

3. The rate of energy production from fat is determined by the rate at which free fatty acids are supplied in the blood. Therefore, the better the circulation to the muscles, the better will be the fat utilization. This is facilitated by one of the adaptations of endurance training (both muscular and aerobic), namely, the increase in capillarization in the muscle.

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