Hi Erogenesis, these two are as close as I can get for the bend and twist without clothing concealing the torso. I have some better ones somewhere.

In the first one you can see the skin stretching accross the abdomen.

In the second one, if Poser did the abdomen sideways pivot, it would lift the other side off the ground, but that is not what really happens.

It is also partly because the spine takes on a sidways curvature, and sags towards the ground at abdomen level. The ribcage stops most sideways curvature in the Thoracic region - not that any figure would be expected to give that sort of finesse, just too many points to manipulate.