I am a practitioner of abdominal breathing and during one of my sessions, I recalled a memory with an old chen teacher of mine. He was talking to the class about abdominal breathing and the roles of ‘heng and ha’ within the taiji form. He then proceeded to tell us that we should try to “Breathe with the Back”. We all sort of looked at him a but funny. The instructor then got into a Chen stance, and then did some abdominal breathing. He gestured to each one of us to come and but our hands on his lower back. To our surprise, his lower back was expanding with his breath!
To this day, I am still unable to do this! I guess it means I need more training or need to relax my core a bit more to allow my diaphragm to expand. I then found the following passage:
When our breathing is full and deep, the belly, lower ribcage, and lower back all expand on inhalation, thus drawing the diaphragm down deeper into the abdomen, and retract on exhalation, allowing the diaphragm to move fully upward toward the heart.
— Source: Deep Breathing Exercises
Come to think of it, I think my abdominal breathing is more focused on breathing with the belly instead of trying to engage my diaphragm!