Kapalbhati is essentially a voluntary abdominal breathing. 'Puraka' and 'rechaka' are gone through in a quick succession with the help of the abdominal muscles. The thoracic part is more or less unmoved as there is no usual expansion of the thoracic cavity. There is no retention of breath in kapalbhati. Rechaka is more important part of this practice. In normal breathing the process of inhalation is active and the phase of exhalation is passive but in kapalbhati, puraka is passive and rechaka is active in nature.
Puraka in Kapalbhati
After raising the chest slightly up, to start with, one just relaxes the abdomen and inhales passively so that the abdomen protrudes out. Immediately after every quick exhalatory stroke of rechaka, one relaxes the abdomen and allows it to bulge out due to the pressure from the abdominal organs. At the same time the diaphragm descends easily, increasing the vertical diameter of thorax. The intrapulmonary pressure is lowered and the atmospheric air rushes in the lungs. No frictional sound is produced in puraka as the air enters passively in the lungs without any force.
Rechaka in Kapalbhati
Rechaka consists of active contraction of the abdominal muscles and at the same time a forceful and rapid exhalation. The abdominal muscles are contracted quickly and vigorously around and slightly below the navel region. This gives a strong inward push to the abdominal organs, which in turn, pushes the diaphragm upward in to the thorax. Diaphragm now exerts an active (positive) pressure on the lungs and the air is expelled out quickly and forcefully. Of course the volume of exhaled air is same to that inhaled in puraka. In kapalbhati there is no resistance to breathing, i.e., both the nostrils are used and the glottis is wide open. The muscles of the neck and the face are kept relaxed so that the air escapes smoothly. Although the friction of the air is avoided in the interior and upper nasal passage and the throat, little friction takes place at the opening part of the nostrils, producing a sound just like one produces during moderate blowing of the nose.
The thoracic part is little elevated and maintained in a relatively fixed condition. It is not expanded with every stroke of the abdomen. If the chest moves with every exhalation, then the air would not be blown properly and the work of breathing muscles would increase unnecessarily. When the chest is maintained in an expanded condition, the force created during rechaka by the quick abdominal contraction, gets an axial direction. The blowing strength of diaphragm increases and the air passage is cleaned more effectively due to the forceful air current. This powerful air current also exerts a suction pressure on all the crevices of the nasal passage and on the opening of the sinuses. This expels the mucous contents and other secretions from this part.
When the abdomen is actively contracted and pushed inward, the pelvic region is also automatically contracted. This results in a strong contraction of the anal sphincters. It is desirable that at least in the beginning one should avoid the formation of Mula Bandha. One may introduce Mula Bandha voluntarily with kapalbhati, after a long practice.
When the contracted muscles of the abdomen are relaxed or loosened, the abdomen bulges out and puraka is done passively. Again for the next rechaka, the abdominal muscles are contracted rapidly and strongly. Thus puraka and rechaka follow each other, moving the abdomen forward and inward alternately. Blowing sound is also produced with each rechaka. The whole process appears like a bellow of a blacksmith.
Thus one cycle of kapalbhati consists of only puraka and rechaka, which are done rapidly, emphasizing more on rechaka. The standard frequency of breathing in kapalbhati is 120 times per minute. The breathing is rhythmic and the speed is acquired slowly by bringing proper coordination of the abdominal contraction and relaxation with exhalation and inhalation respectively. This voluntary control is learnt by conscious practice in the beginning. Normally 10-20 expulsions are gone through in each round in the beginning. The number of breaths per minute is gradually increased over a long practice. After mastering the technique, the recommended speed is achieved. Such rhythmic and well-controlled speed, in this vigorous abdominal breathing, is essential. For all practical purposes, the practice of kapalbhati in this way for half to one minute is sufficient. There should be no undue strain on the breathing mechanism at any stage. The force of expulsions, the speed, the number of expulsions at a stretch in one round, the number of such rounds in one sitting, uniform pitch of factional sound are all properly adjusted consciously, according to one's purpose and capacity.