Maybe these arguments on supination & pronation are made worse by the seriously different definitions of terms. I know I have had a very hard time....believing ISR was pronation for decades until 2011, etc.
The anatomical definitions of pronation
are defined for position
of the forearm and not movement
of the forearm. They reference 0° as a defined position of the "anatomical position". It is very clearly defined. You can search and find these definitions on the internet. In this video the forearm pronation and supination are measured.
2) Common Usage for Rotational Motion in a Direction.
For motion, for a right handed person looking out along the axis of the forearm, pronation is elbow-to-wrist rotation in the counter-clockwise direction and supination is forearm elbow-to-wrist rotation in clockwise direction. That usage is very common, including in biomechanical references. The forearm rotation direction is toward the the same positions as shown in the video above so this usage is closely related to the anatomical definition of #1. You might search and find on the internet, maybe not. If you think this usage is defined please search and provide some links.
3) Tennis Usage of 'Pronation'.
The term is broadly used for the considerable arm rotation that can be seen by eye at the wrist especially at the end of the follow through. This motion in the follow through is mostly pronation (the rotation usage of #2). Leading up to impact, however, there is very little forearm pronation but a lot of internal shoulder rotation (ISR) to provide the largest component of racket head speed. The tennis usage of the term 'pronation' can not be searched on the internet. A dinosaur from the 1970s when people looked at tennis strokes by eye .....I even head Elliott use 'pronation' after his research and publications explained ISR. Since pronation
is not a good term for the ISR of the serve you can't search and find an internet definition to describe how it is being used - its only in the collective tennis wisdom of....
There is a conflict if you think about the definition of #1 and the common usage of #2. If the angle of the forearm as defined is, say, in a position of 40° of supination
but the forearm is rotating in the direction of pronation
- are we sure what everybody means by pronation or supination?
"The Anatomical Position"
- in this position all joints of the body are in their reference positions including supination