As exercise intensifies, the working muscles require an increased supply of oxygen, according to AZ Central. The purpose of oxygen in the muscles is to convert fat into fuel — without it, the muscles would stop functioning within minutes. When a person exercises, respiration increases automatically to bring in more oxygen and expel carbon dioxide, which is a by-product of the muscles' processes.
PT Direct explains the two ways in which the body meets increasing demands for oxygen. The first is to increase "tidal volume," or the amount of air that the body inhales and exhales with every breath. The second is to increase the breathing rate. A person at rest takes an average of 15 breaths per minute, but during a period of intense exercise, this can increase to as much as 40 to 50 breaths per minute. AZ Central says that regular exercise can increase the overall efficiency of the respiration system. A person's resting respiration rate becomes slower as a result of improved air flow volume and increased muscle respiratory strength. The body's gas exchange system is improved, with oxygen being more readily taken into the lungs and bloodstream and carbon dioxide being expelled more effectively. When this equilibrium is maintained, physical and mental health is improved.