A lot has been written about breathing in connection with the Alexander technique; of course, the reason Mr Alexander began his scientific quest was because of his own breathing issues. Investigating the mechanics involved led him to gradually discover fundamental facts about human balance and movement.
In a nutshell, if we habitually clench our neck muscles, the vast weight of our head compresses our spine, our ribs, which hinge in the spine, can hardly move and breathing is impaired. By reversing this process, we can aim for what Alexander referred to as 'thoracic mobility' - infinitely better than so called 'diaphragm breathing' and good old 'upper chest breathing' - a state which comes about naturally in the absence of pressure.
When we organise our muscles effectively enough for thoracic mobility, the diaphragm can move efficiently. This huge muscle is designed to push up when we exhale and down when we inhale - but in most people, most of the time, it moves very little.
When I picture my diaphragm moving, it makes me think of a giant manta ray, unhurried, powerful and majestic. Also, it occurs to me that the diaphragm surely 'massages' the organs above and below - the heart and the stomach - two places that respond terribly to stress.
All sorts of things mess up my 'use' - just being human, I suppose. But for me, the key to an instant return to comfort and calm is through the breath and this image always works for me when I need to free up.