Answer:
Sugar and other starch molecules get stored in the body in the form of glycogen. Glucose is the main energy source that is required by the body during exercise. Complex molecules, like starch and glycogen, need to be converted into glucose during exercise. So, having a carbohydrate-rich diet before exercise is necessary.
The glucose is then used for cellular respiration to generate ATP molecules. About, 36-38 molecules of ATP are generated by aerobic respiration.