Have you seen the Todd Ellenbecker video on shoulders, impingement, serving and other issues? From another thread - "In my interpretation of the Ellenbecker video the issue involves putting the ball of the humerus and attached tissue (suprispinatus tendon, bursa sack?...) in a more confined space under the acromion and then doing the very violent and perhaps sometimes wobbly internal shoulder rotation as shown in this serve video. https://vimeo.com/27528701 The space under the acromion is more confined if the upper arm is high. Acromion illustrations https://www.google.com/search?q=acro...w=1312&bih=703 " Good luck.