Re: Chen Style Seminar Video
Ok. I am thinking the knee up/down is just rotational movement to align his rear leg with the horizontal vector of force.
I also think he can lift his foot while his moment of mass is forward only because there is a equal opposing force, otherwise he'd fall forward.
More, ther would need to be strength to push back, because his leg is at an angle to the horizontal vector of force, the push in the leg mus be greater so xcos(angle) is equal to that force. The stronger opponent wins. Or, if the opponent pushes slightly up making that useless, unless he is ae to some how cause the opponent to push more ore less into the leg in spite of himself, and hopefully more or less imperceptively. In my mind, the gross movement is some sort of shoulder rotation If that were succesful, the opponent is pushing past the shoulder and down. Rotate the trunk unexpectedly and he 'falls' or slips past Not sure if this is accurate, or relates to your point at all.
In an instructional environment, sometimes the effort to allow people to see something you give something else up. Could that be part of this given that his first instruction was not to lean?