Answer:
Your body sends a message to the lungs and tell the lungs to breathe in more oxygen so that the oxygenated blood can travel to the muscles oxygenating the cells within that specific muscle and giving them energy to use the sugars stored in fat or food from digestion. The heart beats faster so that the cells supply keeps up and continues to beat fast for that specific diration of time until your breathing slows down and it no longer needs to work as fast to supply the muscles with as much blood.