I thought I would change gears a little for a moment, so here is a piece on the diaphragm.
The diaphragm is the major muscle of respiration. It is active on an inhale and passive on an exhale. It is dome shaped and attaches to the base of the ribcage and part of the lumbar spine (lower back bones) from the level where the lowest rib attaches to the spine down to the middle of the lower back. The top of the dome of the diaphragm is what is referred to as the central tendon. Above the diaphragm rests the heart and lungs. Below are the abdominal organs.
On an exhale the fibers of the diaphragm relax and lengthen, which causes the dome of the diaphragm to move higher up inside the ribcage. When the diaphragm contracts the muscle fibers shorten and pull on the attachments to the base of the rib-cage and spine. This causes a change of shape in the abdominal cavity and a change in volume (and sometimes a change in shape as well) of the thoracic cavity. Shape change can occur in many ways. These are two common patterns of shape change for the thoracic and abdominal cavities.
1) If the rib-cage is stabilized and the abdominal region relaxed as the diaphragm contracts, the muscle fibers of the diaphragm pulling on the rib-cage will cause the central tendon, or top of the dome, of the diaphragm to be pulled downward (inferiorly) towards the abdominal region and this will cause a displacement of the abdominal organs or, in other words, a belly breath.
2) If the abdominal muscles are held in a flattened position, this will stabilize the central tendon and not allow it to descend and when the muscle fibers of the diaphragm contract pulling on the rib-cage, it will cause the rib-cage to elevate forward and to the side creating an expansion in the thoracic cavity by the change of shape in the rib-cage.
Regardless of what shape change occurs the movement of the diaphragm looks something like the movement of a jelly fish when a jelly fish swims. Unfortunately the contraction of the jelly fish looks like the movement on relaxation of the diaphragm and the relaxation of the jelly fish looks like the contraction of the diaphragm. Oh well. The look of the movement has a quality of breathing anyway. And besides jelly fish are pretty.