The best fuel for muscles are carbohydrates -- either simple sugars (such as naturally occurring sugars in fruits and juices) or complex carbohydrates (the starches in whole grain products, rice, cereal, oatmeal and other plant foods). These carbohydrates provide not only energy but also important vitamins and minerals.
You store only carbohydrates -- not protein or fats - in your muscles in the form of sugar called glycogen. During hard exercise, you burn this glycogen for energy. When you deplete your glycogen stores, as can happen during repeated days of hard training and a low carbohydrate diet, you feel overwhelmingly exhausted. Eating high carbohydrate foods (cereal, pancakes, bread, fruit, vegetables, potato, pasta) on a daily basis can help you train harder and compete better.