What I see is that there are two mechanisms of support for the lower spine, one in the displacement of the fascia immediately behind the sacrum (by the mass of the extensors pressing rearward as they contract, usually in a natural alternation), and another in the displacement of the fascia behind the lower spine by pressure from the “fluid ball” of the abdomen (the term is from D. L. Bartilink). The fascia is the lumbodorsal fascia in both cases, but the coordination of these two means of support is effected by the autonomic nervous system as part of the movement of breath. Looks like this:
This morning I found myself particularly focused on the part of Gautama’s “way of living” that is the experience of zest in inhalation and exhalation, and similarly the experience of ease. He speaks of the body permeated and suffused with such feeling, so that no part of the body is left out.