<P> Exhalation (or expiration) is the flow of the breath out of an organism . In humans it is the movement of air from the lungs out of the airways, to the external environment during breathing . </P> <P> This happens due to elastic properties of the lungs, as well as the internal intercostal muscles which lower the rib cage and decrease thoracic volume . As the thoracic diaphragm relaxes during exhalation it causes the tissue it has depressed to rise superiorly and put pressure on the lungs to expel the air . During forced exhalation, as when blowing out a candle, expiratory muscles including the abdominal muscles and internal intercostal muscles generate abdominal and thoracic pressure, which forces air out of the lungs . </P> <P> Exhaled air is rich in carbon dioxide, a waste product of cellular respiration during the production of energy, which is stored as ATP . Exhalation has a complementary relationship to inhalation which together make up the respiratory cycle of a breath . </P>

All of the air that can be forced out of your lungs following a normal expiration is called