I spend a great deal of time with new students (and honestly, with returning students too) teaching basic ideas about easy, full inhalation and then the appropriate use of that air.
Students often come to the studio so scarred by a) previous teaching that never talked about breath and/or b) choral experiences where the conductor unintentionally signaled high, short breaths.
As part of the retraining, and as a resource, I’m providing this visual reminder:
This German film from 1936 shows the beating heart, the movement of the ribcage, and the action of the diaphragm.
Starting around 1:35, you can really see the diaphragm engaging, causing the vacuum that pulls air into the ribcage. This is coupled with simultaneous external muscle action on the outside of the ribcage, lifting the ribs up. Notice the incredible amount of expansion, and then just how active the diaphragm is on the rapid exhalation too (signaled by the deflation of the lungs). The diaphragm is the dark mass at the bottom on the x-ray.
A side view (starting around the 3′ mark) is instructive, but not in a good way. The sternum is low, and the rib cage is tilting significantly as the subject engages the breath cycle. This is not good! For singing, we need a lifted and stable sternum, allowing maximum air flow and energy.
A 3-D rendering and explanation is quite clear:
Of course, none of this information is discussing what singers need to do well, which is the technique of appoggio.
And for fun, this article on Dummies.com.
A long video about appoggio will require some patience, but it’s worth the watch:
David Dimuzio also discusses breathing in his breathless video:
He’s right! You cannot sing from the diaphragm. Of course, he has the whole thing backward — the diaphragm does not go down because the lungs are filling, but instead causes the inhalation. This video includes a great deal of half-info, but he is right in talking about the tension between diaphragmatic relaxation and the abdominal wall engagement, which is the eternal struggle of appoggio. (Please do not imitate his tonal production, at least in my studio, unless you are thinking more rock-music kind of thoughts!)