Answer:
As muscle activity increases, the muscles require more energy to continue contracting. This energy is provided by the breakdown of glucose and other organic molecules, which generates ATP (adenosine triphosphate) - the energy currency of cells. This process of energy production releases carbon dioxide as a byproduct, which must be eliminated from the body. The muscles also require an increased supply of oxygen to support the energy production. The increased muscle activity leads to an increase in blood flow to the muscles, bringing more oxygen and removing more carbon dioxide. Therefore, to maintain efficient muscle activity, the body must coordinate the delivery of oxygen and removal of carbon dioxide to and from the muscles.