This exercise will enable greater sensitivity for the movement of the respiratory diaphragm, particularly at the posterior margin of your diaphragm deep inside your trunk.
Assume a comfortable seated position so that your spine is upright and stable. Align your cranium, diaphragm, and pelvic floor. Begin by softening the edges of your diaphragm and releasing any strain or holding in your gut. Do you detect any clenching in and around your diaphragm? Breathe into the middle of your back to widen the musculature on the outside of your ribs. At the same time, breathe into the back margin of your abdominal cavity to spread the structures along the inside of your back ribs. Imagine that you are opening an Oriental fan along the bank of your interior ribs, thereby broadening the posterior border of your diaphragm where the blood, nerves, and ingested food pass. Take care not to round or hyper-extend the lumbar-dorsal junction of your spine.
As your diaphragm eases up, you may feel a warm swoosh of blood travel down into your gut and back. It is common for people to clench and hold tension in this area, potentially limiting the free flow of arterial blood into their lower spine. Explore this practice for 5-10 minutes. Afterward, lay down in savāsana, in order to allow your diaphragm and organs to rest.