Breathing is an important function which every human body requires to perform in order to remain alive. Bodies continuously perform two processes that enable them to carry oxygen to and from the lungs: inspiration and expiration. Inspiration is a movement of air into the lungs, and expiration is a movement of air out of the lungs. Tidal volume is the normal amount a body breathes in and out when it is at rest.

The maximal amount of air a body can breathe in and out is called the vital capacity, and it is usually about 1 to 1.5 liters less than the total capacity of the lungs, which is usually about 6 liters, because they can not be completely deflated without serious damage. Residual volume is the amount of air still remaining in the lungs after the most forceful expiration.

Exercise greatly increases the amount of oxygen skeletal muscles use...