I know about wrist pronation, but is it normal to move your wrist in a downward fashion while hitting the ball during a serve? When i was practicing today i suddenly hit a ball while moving my wrist in a downward motion, and it dramatically increased speed and accuracy. It felt very natural and doing so did not strain any of my muscles.
In these videos it looks like Roddick is combining the two, because his wrist ends up pointing down and it has rotated with because of pronation.
What do you guys think? Am i on the right track with the downward wrist movement? Also, can it be fruitfully combined with pronation?