Hi Serendipity.
I don't agree with Terence's definition of "torque". The normal meaning of the word is as follows (this is from Wikipedia)
"""In physics, a torque (ô) is a vector that measures the tendency of a force to rotate an object about some axis [1] (center). The magnitude of a torque is defined as force times the length of the lever arm [2] (radius). Just as a force is a push or a pull, a torque can be thought of as a twist."""
I've not added nor subtracted anything from the Wikipedia definition. Torque is a rotational force about a centre, but that centre need not be stationary.
I also don't understand the idea that part of the body rotates "in the opposite direction (L or R)" to the feet. Why is the word "opposite" in there?.
On your last broom stick model, i would say there is rotation at both connections. But also say that the rotation is distributed (i.e. not at a small number of points)
If you have your feet facing forward but rotate your pelvis, your muscles have to work hard to keep your feet forward (i.e. they apply a torque). When i do this, there is a rotation which feels distributed along my leg (from the stretch i feel) but clearly only happens at the ankle, knee and hip joints.
With the torso, the spine has lots of 'joints'.....
By the way, rotating the spine with good posture is not, or should not be, damaging to the spine.