Upward hand path into impact
The images in this post demonstrate how the hands work up from p6 into impact in order to create parametric acceleration.
Imagine twirling a tennis ball on a rope around and around above your head, then imagine pulling on the rope suddenly creating a burst of speed in the tennis ball as it fly's back over your head.
Or think about how a bushman cracks a whip and breaks the sound barrier, this is parametric acceleration when the centrifugal force gets interrupted.
This happens in the golf swing and it is what allows those who know how to hit the ball enormous distances.
Back to the images, you see the middle image of tiger how his hands are beginning to work upwards.
This can only happen because from the top of the swing P4 Tiger's body works back into flexion, lowering his hands at p6 below where they started at set-up. It is this lowering that allows him to create the parametric acceleration which is the upward motion from p6 into impact.
Body wise this is also why everybody decent stresses the importance of using ground forces.
Lastly for now remember they were saying Tiger had a problem with his head lowering or dipping to much in the downswing, what nonsense, now you know why he did it.