The rotator cuff muscles of the shoulder play a very important role in the prevention of shoulder injury and in the execution of overhead throwing and hitting actions. The four muscles of the rotator cuff are strategically placed so that they are very effective in holding the shoulder joint together.
For example, the supraspinatus on top of the shoulder helps to prevent the arm from popping out when you support your body on your arms. The subscapularis, located in front of the shoulder, helps to prevent dislocation of the arm in front when you bring the arm to side and to the rear. Two muscles on the back of the shoulder (infraspinatus and teres minor) are especially important in the prevention of injury and for execution of some unique arm actions. It is these latter two muscles that are most often injured.
The most important function of the infraspinatus and teres minor (that usually work together) is to control the arm in the follow through after a throwing or hitting action. For example, when you throw a ball, the ball releases close to your ear and leaves the fingers slightly in front of the head. As the ball leaves, the hand speeds ahead of the ball and continues moving forward. The body also continues its rotation so that the arm in essence goes around in a curved pathway in the follow-through.
The hand may release a ball traveling a hundred miles an hour, but yet must stop within a few feet. To slow the hand down in a safe manner requires distance over which the arm can gradually dissipate the forces and slow down. This is provided by the arm action and trunk rotation. At this time the muscles on the back of the shoulder (the infraspinatus and teres minor) undergo a strong negative (eccentric) contraction to withstand and absorb a good portion of the forces.
These muscles contract to not let the arm fly freely forward, but to hold it in check and to guide it under strong muscular contraction. At this time the muscles stretch as they undergo contraction. If they are not sufficiently strong they will stretch beyond their normal length and thus, an injury may occur.
Very often these muscles are subjected a quick and forceful stretch, especially when you throw exceptionally hard. The muscles must then be able to withstand the quick forced stretch; if not, an injury usually occurs.
In hitting actions, similar actions take place. For example, in the golf swing or in the baseball swing when the player takes an especially hard swing, the lateral rotators must slow down the club or bat after contact. If these muscles are not sufficiently strong, an injury will usually occur.
As important as these muscles are in the follow-through, they also play an important role in the preparatory actions, especially in throwing. For example, when you are throwing a baseball, you must first cock the arm. The cocking action consists of lateral rotation in the shoulder joint.
Thus, it is these muscles (teres minor and infraspinatus) that are involved in laterally rotating the arm into position to place the medial rotators (the subscapularis, anterior deltoid and pectoralis major) on stretch. In this way they will be more forceful in medially rotating the arm to bring the ball forward into the release. When the follow-through starts, the lateral rotators once again go into action to control the movements.
Thus, it is very important to strengthen these muscles not only to assist in your performance but also to help prevent injury. Some of the best exercises that can be done are done with a Strength Bar. Hold the strength bar on a straight arm, fully extended in front in different positions and at different heights to more closely duplicate the position seen in your sport.
When in position, medially and laterally rotate the straight arm to not only work the lateral rotators but also the medial. In this way, you strengthen all four rotator cuff muscles to help insure a stronger and safer shoulder joint. Other very important exercises that help strengthen these and other shoulder muscles include the reverse fly (lateral prone raises) and retraction. Lateral and medial rotation with the Strength bar held with the arm in different positions. Many of these exercises can also be done with Active Cords.
For more information on these and other exercises for the shoulder, see Biomechanics and Kinesiology of Exercise.