In yoga, as with all classical yogic practice, one major purpose is to uncover and resolve blockages to improve function. It starts with focusing on the exhalation rather than the inhalation. As one master once said, yoga is really mostly waste removal. This starts with getting rid of the unwanted to make space for what is needed.
Breath as Shape Changing
Breath must be reconciled with posture in order to make such a process effective. Yoga Anatomy by Kaminoff and Matthews defines breath as the shape change of the body's cavities. The two major cavities are the thoracic, or rib cage, and the abdominal, or stomach and pelvis. As these cavities change shape, the spine also changes shape- extending with inhalation and flexing with exhalation. We can understand this by remembering that the spine is the living backside of both cavities.
These two differ in a very important way. The thoracic changes in both shape and volume as more air goes into the lungs (imagine an accordion), whereas the abdominal cavity changes shape like a squeezed water balloon. More food, a baby, or a stuffed colon can change the volume, which is why it can be harder to breathe due to a corresponding decrease in the thoracic cavity.
So with that, Kaminoff and Matthews suggest we imagine the two cavities as an accordion stacked on a water balloon. This means movement in one means movement in the other. If the lower thoracic cavity expands with air, it pushes down on the stomach “balloon” causing it to expand outward. This is one way of describing basic belly breathing.
Sticking with the shape change idea, we can evaluate breath by looking at our capacity to change shape as we breath. Is it constricted or can it change shape freely? It ideally changes shape three dimensionally. So we can ask, in what direction(s) does shape change happen the least?
Contrary to how we normally understand inhalation and exhalation, it is more accurate to say that the universe breathes us. Because the atmospheric pressure outside the body is more than inside your lungs after an exhale, air is actually pushed in. By creating the space through an exhalation, we make it possible for air to be pushed back into us by the weight of the planet's atmosphere. Here's one big reason why yoga says to focus on the exhalation, and not the inhalation. It is because the inhalation takes care of itself simply by exhaling!
The exception to this rule is during relaxed, quiet breathing such as meditation or sleep. During those times, we naturally breath in and the exhalation takes care itself as the thoracic cavity passively recoils back to its initial less expanded position.
The Muscles of Breath
As with any discussion around breathing, we must come to the diaphragm. Click here to see images of it to help follow in the next couple paragraphs. We can understand this muscle as a jellyfish or parachute shaped muscle located between the two cavities. It is a domed muscle, with one side of dome going higher into the thoracic cavity due to the liver pushing up from below and the heart pushing down on the other side of the dome.
The muscle itself is as high as the third and fourth ribs and its lowest fibers (mostly as a central tendon that begins strongly connected to the tissues of the heart) extending along the spine into the lower back. The diaphragm can be understood as a place of anchoring for connective tissue that surrounds both cavities- especially those of the lungs, heart, and abdominal organs. As the diaphragm moves it is both stabilized by these connective tissues and organs, which provide resistance even as they are moved by the action of the diaphragm.
As the diaphragm contracts, it pulls the two extreme ends of itself towards each other. This means that the central tendon connecting to the lower back contracts closer to the base of the rib cage where the dome of the muscle is located. This is how both cavities change shape, which is also determined by which part of the muscle is more stable versus more mobile.
Its important here to remember that all breath is diaphragmatic breath and no breath is necessarily worse than another. Belly breathing is sometimes called the diaphragmatic breath, but that is quite misleading. Belly breathing is caused by the lower attachments of the diaphragm (base of the rib cage) being stable while the domes or upper attachments being mobile. Chest breathing is the reverse of this. If we released muscular action in both cavities, we'd have the belly and chest expanding roughly equally.
Breath training happens when accessory muscles are trained and integrated with the action of the diaphragm. The diaphragm itself is something we have some control over but more with timing rather than starting and stopping- since we can't force ourselves to stop breathing.
Let's take a quick look at the accessory muscles. The internal intercostals, transversus thoracis, and several others pull the rib cage downward, which leads to a belly breath. The lower abdominal muscles stabilize the upper attachments of the diaphragm to create a chest breath. Depending on which type of breath we are doing, one set is tensed while the other set of accessory muscles remains relaxes.
Two other diaphragms are relevant to breathing as well. The pelvic diaphragm makes mula bandha (or root lock) possible, which is a lifting action that stabilizes the lower areas of the diaphragm. The vocal diaphragm is space between the vocal cords, or glottis.
Breath in Yoga
So with all this information, we can start talking about breath in yoga. All three diaphragms (pelvic, respiratory, and vocal) are coordinated in inhalation and exhalation. Working with all three helps create a pressure throughout the back and spine, which can protect the spine during slower movements and stabilize it in others.
In a forward bend for example, breathing with all three helps support the back, providing a pressure that opens up the whole area. This pressure helps with one of the primary purposes of yoga- to uncover and resolve blockages by opening up flow. Without that pressure, we would find ourselves straining and even holding our breath in an unconscious attempt to protect our spine. Continuing with the forward bend example, this pressure creates a single center of gravity supported safely by the legs and pelvis.
Breath in active poses also helps create heat, expansion, power and strength. It also helps us withstand stress. Just think to any time you breathed through something difficult to understand that one. Called brhmana in yoga, it is also related to the chest region, nourishment, prana, and inhaling.
Breath in more inactive poses, such as when we are released, horizontal or doing restorative yoga is called langhana. This helps with cooling, relaxation, release, inward focus, and sensitivity. It is connected to exhaling, elimination and the abdominal region.
Together these help create the balance needed in yoga and life. Bringing in nutrition and removing waste is one way of thinking of this. Such an equilibrium is key for a living organism. Through the breath, we do this by identifying and removing obstructions.
Combined with understanding that good posture is in fact what our body is always trying to do despite our blockages, we can understand the process of breath in yoga as the opportunity to unrestrain breath. Removing the blocakges opens us back up and promotes the healing and balance our body is already naturally moving towards. In other words, unrestraining the breath is the same as identifying and releasing tension.
So in fact breath is our best, most available teacher in yoga.