Originally Posted by Say Chi Sin Lo
First of all, it helps if you've got punctuation here and there. Good god, my eyes hurt. A paragraph is a paragraph, not an entire sentence.
I hope I can understand you and help. After an eyesore of a read, it sounds like you are lacking significant internal rotation of the shoulder. The "arm-behind-the-back" is a good indicator of internal rotation of the rotator cuff. The further up you can slide your hand up, the more range of motion you have.
Use a towel with your off-hand, and grip the towel with the hand behind your back, and slowly use your off-hand to pull the arm behind your back up.
Your shoulder maybe mechanically sound, and you claim to have shoulder problems despite the lack of structural damage. It sounds like there is significant muscle imbalance. Uneven tightness within a joint can cause a lot of stress.
So, there are two things for you to do, stretch your internal rotators, followed by punctuation.
Sorry I'm usually very good about my grammar and punctuation; I wrote that after getting up from a long needed nap and stretching out some stiffness. Thanks a ton on the advice I'll definitely be using that stretch from now on in my normal routine.
Sorry for hurting your eyes!