Notice that exercise is vitally important for a healthy life. The body is made up of cells. Every function carried on by the body is directly related to the life of the cells. Each muscle in the body is made up of individual muscle cells. Since all cells require energy to function, any movement by these muscle cells requires energy.
All cells use amino acids and fatty acids combined with a glucose and oxygen to make energy.
Amino acids come from protein, and fatty acids come from fats, while glucose comes from sugar and oxygen from the air we breathe. Thus, for the muscle cells to function, they need a sufficient amount of acids, glucose, and oxygen. The more energy the muscle cells burn due to exercise, the more acids, glucose, and especially oxygen is necessary to allow the cells to continue moving in exercise. Oxygen can only be supplied to the muscles through the red blood cells. When muscles are being used in good exercise, the heart must pump more blood through the body to supply the extra need for oxygen.