Most often, shoulder pain can be traced to tenderness or soreness of the rotator-cuff tendons. The rotator cuff is the part of the shoulder that allows you to move your arms in a circular motion. It also helps to stabilize the shoulder joint also known as a gleno-humeral joint (HG joint).
In other cases, the subacromial bursa, or fluid sack, in your upper shoulder can become inflamed after a period of heavy lifting or other kind of physical activity involving repeated raising and lowering of the arms. This type of pain is worst when trying to lift your arm above your shoulder.