This is an excerpt from Yoga Anatomy-3rd Edition by Leslie Kaminoff & Amy Matthews.
It should be clear by now that belly breathing is only one type of diaphragmatic breath—one in which the base of our rib cage (lower attachments) is stable, our abdominal wall is released, and the domes (upper attachments) are mobile (see figure 6.17a).
If we reverse these conditions by stabilizing our abdominal wall while releasing our rib cage, a diaphragmatic contraction exerts a lifting action at its lower attachments and an expansion of our rib cage (see figure 6.17b). This is usually called a chest breath, which many believe to be caused by the action of muscles other than our diaphragm. Chest breathing has gotten a bad reputation because it is associated with stress responses, while belly breathing is lauded for its calming effect on the system. While this may be true for many people, it is not true universally. It is just as possible to take a relaxed, efficient chest breath as it is to take a tense, tightly bound belly breath. In short, the location of breathing’s shape change in our body is not a reliable indicator of how beneficial it is, so labeling one location of shape change as healthy and the other unhealthy is not justified. (See Cueing Callout: Exhalations Are Not Always Calming in chapter 7.)
This mistaken idea creates a false dichotomy between diaphragmatic and so-called nondiaphragmatic breathing. Except in cases of paralysis, our diaphragm is always used for breathing, so the term diaphragmatic breathing is a redundancy that reinforces this dichotomy.9
Breathing is what we do with our diaphragm, just as assuredly as walking is what we do with our feet.10 We don’t start a class in gait training by telling students they have been walking improperly and are about to learn foot walking. Yet, breathing students are commonly told they’ve not been using their diaphragms until they are taught the correct method of belly bulging known as diaphragmatic breathing.
The real issue is whether our diaphragm is able to work efficiently, meaning how well it can coordinate with all our other muscles that affect shape change. Yoga practitioners can achieve this more easily if they are not misled by confusing terminology.
9. Yoga technique includes a version of non-diaphragmatic breathing—kapalabhati—which requires our diaphragm to relax so it can be moved by our abdominal viscera powered by rhythmic contractions of our lower abdominal wall.
10. The example of people with paralyzed diaphragms or lacking feet who, with the aid of technology, still manage to breathe and walk are exceptions that prove the rule.