Do you have sudden weakness in certain shoulder movements? Sudden weakness in external shoulder rotation with or without pain may be related to irritation of the suprascapular nerve. It’s a nerve that comes from the neck and travels through the shoulder blade. It controls the external rotators of the shoulder including the Supraspinatus and Infraspinatus rotator cuff muscles. So when this nerve is irritated either through entrapment or major repetitive trauma it can lead to major weakness in shoulder external rotation, muscle wasting and pain. In most cases all other shoulder movements are preserved and pain free. Getting you back to tip top shape requires professional advice and an exercise rehab program, so if you do feel you have these symptoms get some professional advice!