You can do it standing, with your elbow at a 90-degree bend, and both of them out in front of you, you're going to compare supination, or palms up, versus pronation, or palms down. So for example ...

5 Internal rotation of the upper arm at the shoulder during the service and forehand is of utmost importance; decrease of internal rotation in the shoulder can increase rotatory stress on the elbow.

Eccentric exercises: Slow progressive eccentric exercises for LET should be performed with the elbow in extension, forearm in pronation, and wrist in extended position (as high as possible). However, ...

[5] During the arm stabilisation test, the presence of a pronator drift, a mild elbow flexion and passive ... downward as a whole rather than in a pronation movement [6,7] has thus been seen ...