STS Bending

I was practicing the beginning of the san ti shi with the bend and coordinated arm movement. I was trying to not float from the crown point, not sure if I was doing it correctly or not but the thing I was noticing was that when I was unbend and the arms would go down I could feel a stretch or like a rubbing against the lower back/ribs along the side of the back. It was more pronounced on the right side but I could feel it faintly on the left side as well. Is this related to the transverse couple or is this just a passing sensation.

Torsion image from Wikipedia