I can't tell you how many times I've been training with someone or around someone and they complain about their shoulders. Honestly, it's a huge pet peeve of mine because 9/10 times they did it to themselves through simply skipping that all important warm up of the rotator cuff when training shoulders. The rotator cuff is a group of four muscles that stabilize the shoulder and allow it to move. To sufficiently have a successful career in the gym, one must pay mind to the health of their rotator cuff. Check out the link for some awesome exercises. http://www.