Scapulohumeral Rhythm

Scapulohumeral rhythm is needed for efficient arm movement. It is the relationship of movement between the scapula and humerus. The ratio for scapulohumeral movement is that for every 3degrees the shoulder is moving, there is 1degree of movement at the scapulothoracic joint, and 2degrees of movement at the glenohumeral joint. The scapula and humerus movements want to be synchronized. This rhythm allows the muscles involved to be in the optimal length tension relationship. The rhythm helps maintain the subacromial space, and helps make sure there isn’t an impingement to the space. It there were an impingement in the subacromial space, that could lead to injury, or damage to the supraspinatus muscle.  For the shoulder to have full range of motion, the humerus head needs to rotate laterally and it does that with help from the rotator cuff muscles (Infraspinatus and teres minor). In this rhythm, motions are distributed between to joints, which helps have a better range of motion. The joint congruency results in decreased sheer forces. The rhythm also helps prevent active insufficiency on the muscles moving the glenohumeral joint.