Muscle cells require more energy during exercise. Energy is made during respirationThe chemical change that takes place inside living cells, which uses glucose and oxygen to release the energy that organisms need to live. Carbon dioxide is a by-product of respiration..
When exercising, cells will need more oxygen and produce more carbon dioxide as a result of increased respiration.
When blood reaches the lungs, a larger volume of air is needed to replace the oxygen used and remove the carbon dioxide produced by this extra respiration.
In order to supply more oxygen to the exercising cells, the body increases the rate and depth of breathing.
The time taken for the breathing rate to return to normal is known as the recovery time.