 There are three things that are really hard on your shoulders that can cause you pain. If you have rotator cuff problems, these will make them worse. One is lifting over shoulder level, over shoulder height, particularly with weights. Muscle lifting far away from your body puts huge amounts of stress on your shoulder. And then the other things that are really stressful are things that are like planks or push-ups or pull-ups. Planks are not quite so bad because they're not full body weight, but push-ups are particularly hard on your shoulders.