Scapulohumeral Rhythm

The shoulder is known to have the greatest range of motion in the body. Scapulohumeral rhythm is defined as the ratio of movement between the scapula and the humerus during shoulder elevation. Thus to maintain optimal range of motion of the shoulder the humeral head must rotate laterally on the scapula. The motion at the shoulder is distributed between two joints which is important for scapulohumeral rhythm. The two main joints that are involved are the scapulothoracic joint and glenohumeral joint.  It is important to note that for every 3 degrees of shoulder movement there is 1 degree produced at the scapulothoracic joint and 2 degrees produced at the glenohumeral joint. This is important because if the joint ratios are not working together properly it can cause deficiencies in shoulder function.

In clinical reference scapulohumeral rhythm serves two purposes. The first purpose is that it allows the glenoid fossa to maintain a good position for all the various movement of the humerus. The second purpose is that the changing position of the glenoid fossa permits good length-tension relationships. Thus making it important when assessing muscle function and range of motion on a client. In order to maintain this rhythm it is important for the clinician to keep the muscles that are in relation to the humerus and scapula strengthened to avoid dysfunction. It is also crucial to help maintain the subacromial space to avoid impingement on the tendon of the supraspinatus muscle, long head of the biceps brachii, subacromial bursa, and the joint capsule.