Sorry, but this is wrong.
What injures the UCL is supinating the forearm as the elbow is rapidly extending. This causes two problems. First, it puts a twisting load on the UCL. Second, it focuses the load on the UCL (rather than letting the load being taken up by the bony structure of the elbow or muscles like the Pronator Teres).[/quote]
Chris, I think we’re saying the same thing. My “Supinating during forward acceleration” is the same as your “supinating the forearm as the elbow is rapidly extending”. There is a tremendous amount of force applied to the arm and adding in a twist while all that force is being applied is part of the problem. The other part is the rapid change of direction in rotation of the arm from a supinated position to the pronated position immediately after release.
As I said before, getting the arm into the supinated position BEFORE it starts forward removes the twisting forces DURING the forward acceleration and it eliminates the change in direction of rotation of the arm after release. All rotation is in the pronation direction - there’s just more rotation (180 degrees instead of 90 degrees as with a fastball).