Overhead presses, lateral raises, chins, and a host of other exercises can cause another problem when done with sloppy form. You actually compress the tendon repeatedly, creating an inflammatory response leading to tendonitis and impingement syndrome. The good news is strains and tendonitis are both preventable and treatable. Just as sloppy lifting can make the shoulder joint more unstable, slight changes in lifting technique can profoundly stabilize it. Maybe you even got your knuckles rapped once or twice.
Posture is extremely important.
While standing straight, pull your shoulders back and squeeze your shoulder blades down and together. In this position, your scapular muscles anchor the shoulder, providing the most stability. Every shoulder and chest press, lateral, and fly should be performed with your chest high, shoulders back, lower back arched, and shoulder blades together. Keep that position throughout the motion. Initially, you may need to lighten your poundage to practice and perfect these movements.