Carbohydrate is an important energy source during exercise. During short, heavy exercise it may be the only energy source for the working muscle and may be derived exclusively from the glycogen stores within the muscle fibers themselves. During prolonged, submaximal exercise the magnitude of the contribution that carbohydrate makes to the total fuel consumed depends upon a number of factors, including (1) the intensity of the exercise, (2) the duration of the exercise, (3) the state or type of training that the individual has engaged in, or both, and (4) the diet previously consumed. Due to their limited storage in the body and the relative ease with which these stores can be manipulated by combinations of diet and/or training, a knowledge of the dynamics of carbohydrate metabolism is an important component in the arsenal of knowledge for coaches and athletes.