To bring air down into the depths of the lungs, it is not actually necessary to take a big breath, as even the quietest of breaths will activate the diaphragm. When you are practicing abdominal nasal breathing, you should not be able to see or hear your breath during rest. In contrast, overbreathing through the mouth, in an attempt to take a “deep” breath, will be clearly audible and cause the chest to rise and fall, but will still not manage to draw the breath deeply into the lungs.
