The process by which gas is expelled from the lungs (see respiratory movement). In mammals, the volume of the thoracic cavity is reduced by contraction of the internal intercostal muscles and relaxation of the muscles of the diaphragm, assisted by upward pressure of the abdominal organs. As a result, pressure in the lungs exceeds atmospheric pressure and gas flows out of the lungs, allowing the pressures to equalize. Compare inspiration.
Subjects: Sports and Exercise Medicine — Biological Sciences.