After a few long, slow, deep exhalations there is an automatic tendency to breathe in more deeply from the stomach.

We are going to try to accentuate this tendency as far as possible. It is important to empty the lungs thoroughly, thereby getting rid of the greatest amount of air.

This piston-like structure is however not rigid, and unlike that of a motorcar is not flat, but convex rather like the lip of a casserole dish. The diaphragm has a rather rigid, flat central section - the aponeurotic - and is surrounded by a girdle of peripheral muscles whose contraction determines its downward movements: the diaphragm muscles are among the strongest in the human body, or perhaps we should say, they are designed to be the strongest, because their owner alas, may allow them to atrophy.

We can also understand why complete relaxation is only possible once the lungs are emptied without forcible exhalation - because at that moment the diaphragm muscles are at rest.