Why do people breath harder and the heart beats faster the more you exercise?

Our bodies burn fuel much like a car does. When you press on the gas, more fuel and air is sucked into the engine and combusted to produce more horsepower. When we exercise it is like we are pushing down on our own accelerator pedal that pumps more sugar and oxygen into our muscles to produce more power. Our heart rate and breathing increases to allow us to burn more of our fuel which, instead of gas, is adenosine triphosphate (ATP).

The science is that when we exercise our muscles need more energy and oxygen to move and so we need to breathe more air. Then the air goes down the trachea, through the bronchi and bronchioles and finally into air sacs called alveoli where the oxygen is diffused through the thin walls of blood vessels called capillaries. At the same time carbon dioxide is diffused through the wall from the blood vessel to the air sac and back out the same way the oxygen came in. Then the oxygen is transported around the body through the blood vessels and into the muscles.Then the deoxygenated blood goes to the heart and lungs to become oxygenated. This supplies oxygen to all the body tissues. As more energy is needed in the muscles more oxygen is needed in the blood so respiration increases.

When you exercise, your muscles need more oxygen and fuel to continue working. Your heart rate then increases to get more fuel and oxygen to them more quickly. Depending on how hard you are exercising, your heart will speed up accordingly to give your muscles the power to keep going.