What exactly does this mean? It appears numerous times throughout the Bikram dialogue:

Utkatasana: "Suck your stomach in, hold it in." "Suck your stomach in, compression of the abdominal wall, contraction of the abdominal muscles." "Exhale breathing, suck your stomach in, spine straight."

Garurasana: "Suck your stomach in."

Dandayamana Bibhaktapada Paschimotthanasana: "Suck your stomach in"

Dandayamana-Bibhaktapada-Janushirasana: "Exhale breathing, suck your stomach in"

Tadasana: "Stretch your spine up to the ceiling, and suck your stomach in."

...and possibly more.

In other traditions there are discussions of the bandhas, which I believe might offer a better explanation. The reason I ask is there is 1) a sort of collapse or lifting of the diaphram where the belly is pulled deep into the torso cavity and the ribs are exposed. This however, is a bit of an exaggeration and doesn't lend well to engaging the core. 2) There is a tucking or knitting of the ribs, the use of the upper abdominal area. It's also a tuck of the pelvis -I jokingly refer to this as what the male Calvin Klein model does in just underwear. 3) Then there's the tightening of the lower abs, more in line with mula bandha I think.

Both 2 + 3 from above be applied together and lend very well for asana requiring core energy. Yet 1 is what I think of when I hear "suck your stomach in" and 1 does not mix wither either 2 or 3.

Does this make sense? Is this just another (yet another) dialogue issue?