Originally Posted by gzhpcu
I think some of the misunderstanding is perhaps due to misidentification of biomechanical definitions:
Pronation alludes solely to rotation of the radioulnar joint at the elbow around a superoinferior axis, and is confused with internal shouder rotation which occurs at the shoulder.
Seems to me that the active internal shoulder rotation results in the passive pronation if the arm is kept loose...
To be clear: we are talking about multilevel movements around two separate joints - shoulder and elbow
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.