Scapulohumeral Rhythm

The Scapulohumeral Rhythm is the ratio of movement between the scapula and humerus during shoulder movement -- for every 3° of shoulder movement, the scapula moves 1° and the humerus moves 2°. For example, if the shoulder moves in 180° of shoulder abduction, the scapula moves 60° and the humerus moves 120°; it is a simple math equation. The Scapulohumeral Rhythm is incredibly important for normal, healthy shoulder movement. Normal Scapulohumeral Rhythm allows the glenoid fossa to rotate upward and maintain a stable connection with the head of the humerus, as the scapula is rotating upward. In addition, the scapula needs to tilt back and laterally rotate to allow this motion of the humerus, and to achieve full range of motion. Full range of motion in the shoulder is important for reaching for things up off of a tall shelf, for example. Next, the Scapulohumeral Rhythm also allows the rotator cuff muscles to maintain an optimal length-tension relationship - these muscles' tendons reinforce the joint capsule. Scapulohumeral Rhythm can also maintain the subacromial space (biceps long head, supraspinatus), which prevents impingement. Finally, normal Scapulohumeral Rhythm is necessary for efficient arm movement. The Scapulohumeral Rhythm allows us to move our shoulders, in all three degrees of freedom, in order to easily participate in the occupations that are meaningful to us in our daily life.