Reverse breathing: the ilio-lumbar ligaments (yellow) engage in the movement of breath.
The autonomic respirations coordinate through the place of occurrence of consciousness (illustrated with a gyroscope) to cause action that opens the nerve channels between vertebrae; thus, the place that consciousness occurs has impact and opens feeling, through the body to the surface of the skin and in the senses.
We all know what it feels like to stretch, and how close stretch can be to pain; a lot of my practice is learning what is stretching at the moment, and how to relax and allow stretch and activity to reciprocate as consciousness takes place. The length of the movement of breath can be a guide to healthy stretch and the subsequent involuntary activity, both with the breath in and with the breath out.
With that in mind, the impact and feeling as consciousness takes place in inhalation tends to result in reciprocal activity that draws upward and inward, while the impact and feeling as consciousness takes place in exhalation tends to result in activity that sinks downward and forward. This is my experience, when the length of the movement of breath guides the stretch and activity as consciousness occurs, and I believe this is because the ilio-lumbar ligaments from the pelvis to the 4th lumbar vertebrae engage on the inhalation (they are vertical), and the ilio-lumbar ligaments from the pelvis to the 5th lumbar vertebrae engage on the exhalation (they are horizontal).
When the length of the movement of breath guides the stretch and activity as consciousness occurs, reverse breathing is already taking place, even though each breath is completely natural.