The chest is depressed by its own weight, expelling the air. At the end of the expiration the abdominal muscles help the lungs to empty to their fullest extent, by means of a contraction which expels the last traces of tainted air. The more complete the exhalation, therefore, the greater the quantity of fresh air to enter the lungs, and so the purer the air in contact with the alveolar surfaces. A more apt term cannot be imagined, and innumerable techniques have been thought up aimed at increasing this capacity. Before we can contemplate this improvement we must make use of what we already possess by carefully exhaling.
Yoga recognizes three separate forms of breathing - diaphragmatic, intercostal, and clavicular.
Complete yogic breathing combines all three, and constitutes the ideal technique. The majority of men breathe in this way. The diaphragm subsides while the breath is drawn in, and the abdominal region swells. This is the least faulty method of breathing. The base of the lungs fills with air, and the rhythmic lowering of the diaphragm produces a constant, gentle massage of the whole abdominal content, and helps these organs to function correctly.