The simple facts-

1.Every pitcher pronates.
2.Pronation is less or more from one pitcher to the next.


That said, it may be easier to discern the real and true cause of pain. The cause of the pain really has nothing to do with what happens after the release and deceleration of the arm in my opinion. The action of the arm done up to the release of the ball is the sole cause of arm pain I believe.

What we are really talking about is how violently or smoothly the joints are working together up until and at the moment of release. How much the arm pronates and bends inwards after release only tells us the tale of what was happening up to that point! A lot of pronation and arm bending is a sign of good fundamentals and a smooth arm action. Little pronation and arm bend in the follow through is a sign that the fundamental mechanics of the pitching sequence are breaking down. It is a sign that a pitcher is pitching with more arm than body.

Teaching good and early hip rotation and releasing the ball at the exact moment are critical to prevention of arm strength and pain free operation.

I watch my son and others pitch and notice that the more smooth the arm looks in the natural arch, they are pain free and have good natural pronation and arm bend. When a pitcher starts getting tired their body stiffens and the arm gets more jerky at the moment of release leading to poor pronation and arm bend.

That all said, it may be true that arm injuries are caused solely off of over exertion leading to bad release points and mechanics that are harmful to the arm. Pitchers as they wear start to jerk the arm more to the focal point of their delivery at the release point. That jerk literally makes their joints collide violently together too fast. I have since found to watch the motion and plane of the arm to see if it is working with the rotating hips or against them.

I have found that most of the time arm pain from pitchers has been from trying to "overthrow" and that the cause in the arm is due to the arm violently jerking and moving outside of the timing and connection of the hips.