Taiji figure 8 training

The figure 8 training method is to draw a figure 8 on a horizontal plane while you're in a horse stance, using your body as the pencil, and the butt as the pencil tip (or more precisely, the bottom of the vertical axis running through your body as the pencil tip). Please let me know if you have a good picture to illustrate this. My drawing skills are somewhat limited bordering on non-existent!

Anyway, my previous encounter with this training method was just to draw this figure 8, to train the legs and to train turning the body. Recently, I was asked to revisit this method again, but this time the kua should not protrude. This criteria was not previously included. By including this criteria alone, the intensity of the training is so great that I can't last more than 1 minute of it!

The protrusion of the kua was something recent to me. It is whenever the kua is not relaxed that there will be some protrusion, i.e. some tension at the kua. To resolve this, my current teacher suggests (among other things!) to try out this figure 8 training method.

If you have tried this before, or even if you haven't, please let me know if you are having similar experience. Just be careful about the knees, as the training may seem like drawing circles with the knees.