Ramacharaka

“The following simple exercise will give you a clear idea of what the Complete Breath is: (1) Stand or sit erect. Breathing through the nostrils, inhale steadily, first filling the lower part of the lungs, which is accomplished by bringing into play the diaphragm, which decending exerts a gentle pressure on the abdominal organs, pushing forward the front walls of the abdomen. Then fill the middle part of the lungs, pushing out the lower ribs breastbone and chest. Then fill the higher portion of the lungs, protruding the upper chest, thus lifting the chest, including the upper six or seven pairs of ribs. In the final movement, the lower part of the abdomen will be slightly drawn in, which movement gives the lungs a support and also helps to fill the highest part of the lungs. At first reading it may appear that this breath consists of three distinct movements. This, however, is not the correct idea. The inhalation is continuous, the entire chest cavity from the lowered diaphragm to the highest point of the chest in the region of the collar-bone, being expanded with a uniform movement. Avoid a jerky series of inhalations, and strive to attain a steady continuous action. Practice will soon overcome the tendency to divide the inhalation into three movements, and will result in a uniform continuous breath. You will be able to complete the inhalation in a couple of seconds after a little practice. (2) Retain the breath a few seconds. (3) Exhale quite slowly, holding the chest in a firm position, and drawing the abdomen in a little and lifting it upward slowly as the air leaves the lungs. Where the air is entirely exhaled, relax the chest and abdomen. A little practice will render this part of the exercise easy, and the movement once acquired will be afterward performed almost automatically.”
― Yogi Ramacharaka, Science Of Breath - A Complete Manual of the Oriental Breathing Philosophy

“but say that in addition to the physical benefit derived from correct habits of breathing, Man's mental power, happiness, self-control, clear-sightedness, morals, and even his spiritual growth may be increased by an understanding of the "Science of Breath.”
― Yogi Ramacharaka, Science Of Breath - A Complete Manual of the Oriental Breathing Philosophy