Rotator cuff tendonitis is a common condition affecting many patients who have an active lifestyle. Most commonly it is caused by either overuse of the shoulder or overloading of the shoulder muscles. An overuse injury commonly occurs in overhead sports such as swimming or throwing sports (baseball, football, tennis). Also, any line of work or hobby that requires the worker to do repetitive overhead work or lifting with the hands out away from the body, such as construction or manufacturing, predispose patients to overuse injuries of the shoulder. In contrast, overload injuries to the shoulder occur as a single event when a rapid forceful jerk or pull quickly moves the shoulder and the resisting muscles. This may occur with something as simple as a dog bolting while on a leash or catching oneself to break a fall.