Respiration complète du yoga : n'a pas grand-chose à voir avec une respiration naturelle optimale.

(Complete Breathing, Complete Breath)

There are probably several variations on this but this one is the one I see most of the time.

The standard yogic precept is that inhalation is made up of three partial phases:

1. Diaphragmatic or abdominal breathing induced by lowering and flattening the dome-shaped diaphragm causing the belly to protrude..
2. Intercostal breathing is brought about by expanding the rib cage as the belly comes inward to force the breath upward.
3. Clavicular breathing from the top of the lungs, produced by raising the upper part of the thorax.

Supposedly each of these phases has its own merits, but in theory yogic inspiration is only complete when all three are done in proper sequencing  This by the way has little to do with optimal natural breathing.

Before attempting to combine them - that is to say before we can achieve in one single, smooth and continuous movement complete and easy filling of the lungs, thereby supplying them with reviving air, and expanding the pulmonary alveoli (all 70 million of them) - we must learn to properly integrate the three phases. First of all we practice breathing PROPERLY from the diaphragm.

Just as you can not tell someone what chocolate tastes like -they must taste it themselves- this can not be described in words or pictures. It MUST be felt as in a felt sense such as Eugene Gendlin talks about in his Focusing. 

First Learn the fundamentals