Forehand Topspin wrist

I've already searched for all questions and answers at pingskills.com; I've looked Jeff and Alois at training video, but I still feel doubt.

http://www.youtube.com/watch?v=_ppw7NT9g1w [Wang Liqin]

http://www.youtube.com/watch?v=8kqzzLM4jAc [Jeff]

http://www.youtube.com/watch?v=kE7V8btXe6E [Stefan Feth]

Please help me analyze those three videos.

Wang Liqin, Jeff, and Stefan Feth, was doing the same brush contact and snapping their forearm. However, they have the same wrist movement, I think. After watching those video for thousand times, slow it down, I can't do the same thing.

The racket going fast from steady state; due to the moment inertia, the first Newton's Law, and aerodynamic; when I snap my forearm, the fast and sudden movement, due to the surface of racket is vast, the air friction tend to "open" the racket; and I did an upward movement. My wrist is loose.

Now look at the video, indeed, Wang Liqin, Jeff, and Stefan Feth, was snapping their forearm when their bat's surface contact the ball, but their wrist when the bat contact the ball did not shake. They collect the energy from mass body at their right legs, transfer it to the right arm, and like throwing the heavy load, BOOM! But their wrist do not shake when they snap. They slightly lift their wrist a before they snap the ball, but their wrist do not shake when contact the ball.

Because of "tremble" wrist when contact the ball, sometimes I do not generate heavy spin, although it's an upward motion, it's disturb the clean brush contact; sometimes because of tremble wrist my shot isn't controllable and I can't place the ball. I do not blame Newton's law and aerodynamic, but if I strengthen my arm, it won't go fast. But if I accelerate the loose wrist, my wrist will slightly tremble.

Assume that I do the forehand topspin exactly same as Jeff do. My problem is my wrist.