Think you may have got this round the wrong way. Moving your thorax makes the chair go the opposite way. So the rotation of the thorax automatically puts the brakes on the pelvis.
No bud, I understood that. I saw this analogy 5 years ago and originally believed it. To clarify, I can accelerate the thorax in one direction without the chair going in the opposite direction and with the chair going in the same direction. No causality.
Edit: I can of course adhere to the opposite direction claim.