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Old 03-03-2011, 01:16 PM   #68
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Join Date: Sep 2009
Location: Toronto Canada
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Originally Posted by Chenx15 View Post
This guy got it absolutely right. Pronation/supination is only applicable to the forearm. while the actual movement of the serve is the internal rotation of the shoulder which in a way is also pronating the forearm.
yep, as I wrote in my other thread:

Forearm pronation actually contributes relatively little to racquet head speed - rather, it is internal shoulder roation that achieves this (this is counterclockwise rotation of the upper arm). Because the forearm is colinear with the upper arm, and because the forearm tends to adopt the same motions that the upper arm generates, internal rotation of the shoulder achieves a very similar effect upon the racquet as pronating the forearm does.

This is true only if the forearm and upper arm are colinear, as in the below images. In both these pairs of images, the forearm is NOT pronating - the only rotation is the shoulder internally rotating.
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