Lumberg said:
That sounds like the rule could be open to interpretation, as far as where the thighs end and the butt begins.
And yes I have seen some photos of chinese female PLers who I swear could pursue alternative careers as contortionists. We'er talking a lower back that is like a foot off the bench. Incredible.
I've heard that somewhere people practise their arch with a deflated ball. As they get better at it they put more air into the ball ---> more arch and so on and so on....