This is what is got from looking at my shifu and what he taught me.
He says, "In Brush Knee Twist Step, as one hand brushes downward, and the other hand is placed near to your ear, there is a slight twist in the waist area. It is chou(pulling and collecting), which causes the eventual hit to have power."
In my opinion, it is like storing energy in the side of the body which the hitting hand is on. In actual fact, i feel it is like shifting the centre of gravity to that side of the body and like throwing it all out in the hit. As the waist turns, imagine it is a spring and it stores up energy, ready to release it all out at one go.
From what i observed of my shifu a few days ago, when my shifu's hand moves from the ear area to the front to bring in the hit, his belly moves from the side to the front together with his hand(quite obvious as he has a big belly). From my point of view, it seemed like his whole centre of gravity was linked to his hand and if someone got hit by that palm, it would feel as if he was hit by my shifu's whole weight and momentum.
Another thing to mention here is when the hand is placed at the ear, ready to go in for the hit, some people(my shifu 2ic) usually places his hand with his palm facing forwards and outwards. Then as the palm moves forward, it slowly turns in until the palm's final position is with the fingers facing upwards( meaning the palm is upright). The rationale behind this method is that the palming method is the corkscrew method commonly seen in Chen Style with Chan Si Jing.
While from my readings and insights, the palm is usually placed near the ear, with the palm facing inwards, forwards downwards, like sort of facing the forward leg. Of course maintaining a seated palm(Zuo Wan). Then it slowly rotates to the upright position as it pushes out. I think that the use of this is so as to be able to deflect any incoming hit to any other direction (downward or sidewards) it may even be used as an entry into another Brush Knee Twist Step. Then if it is a successful straight blow, it delivers the Chan Si Jing in a reverse corkscrew movement.
One thing worth noting is that in any of such palms, your palm cannot go out with the palm being directly perpendicular to the ground i.e. solid. It must have sort of a solid yet not solid kind of character so if a solid hit comes, you can still absorb or deflect or redirect it. Basically, if your palm starts out solid and encounters a solid, both are sure to suffer.
