Scapulohumeral Rhythm

The shoulder is the most mobile joint in the body. It is a combination of several articulations: the glenohumeral, scapulothoracic, sternoclavicular, and acromioclavicular joints. Each of these contributes to shoulder and arm movement via a process known as joint “coupling.” For example, when you raise the arms over the head in Urdhva Hastasana, the clavicle pivots on the sternum (breastbone), the scapula rotates on the chest wall, and the head of the humerus moves within the shoulder joint. All of these work together simultaneously in what is known as scapulohumeral rhythm. In general, 60 degrees of this action comes from movement of the shoulder blade on the chest wall (scapulothoracic motion) and 120 degrees from the ball and socket of the shoulder (glenohumeral motion). During this process, the clavicle rotates on its long axis approximately 25 degrees and the humerus externally rotates about 45 degrees. Scapulohumeral rhythm is illustrated in the video below, with a breakdown of scapulo-thoracic and gleno-humeral contributions to the entire movement. http://www.dailybandha.com/2011/04/sh...