There are three factors which predispose you to rotator cuff tendonitis: a weakness or imbalance of the muscles around the shoulder; a lack of endurance in the muscles of the rotator cuff to perform the given task; lack of flexibility which decreases the rotator cuff’s ability to sustain forces exerted upon it.
The first cause is typically seen in football players or body builders who bulk up the large muscles around the shoulder (deltoid, biceps and pectoralis) but neglect the rotator cuff muscles. The pull of these large muscles overcome the ability of the rotator cuff to keep the humeral head located in the glenoid and it subluxes or slides out of the glenoid causing added stretch and injury to the tendons. When this is repeated numerous times it causes micro-tears in the tendon. If ignored, this can lead to a damaged rotator cuff.
The second cause is usually seen in the golfers or tennis players who go out and play more than they are accustomed, an extra nine holes or that extra set. Pitchers and quarterbacks are prone to this when they are at the end of a game and have thrown more than usual. Typically, as you continue past the point of endurance the arm becomes heavy and numb. Pitchers refer to this as “throwing their arm out”.
The third cause is prevalent in throwing athletes in their dominant arm. So much force is generated when throwing a ball to the plate or throwing to the end zone that the fibers of the tendon separate. As the tendon heals, it contracts and tightens. As this is repeated over the course of a season, the player actually loses range of motion in their shoulder.
In Part III, we will discuss ways in which the likelihood of shoulder injuries can be reduced.