Scapulohumeral Rhythm

The scapulohumeral rhythm describes the synchronized movement between the scapula and humerus. The scapula must move in order for the glenoid fossa to maintain contact with the head of the humerus. The scapula and humerus move at a 2:1 ratio; therefore, when the shoulder moves through full 180° of motion, the scapula rotates upwards 60° at the ST joint and the humerus moves 120° at the GH joint. This distribution of motion allows for efficient arm movement and an optimal length-tension relationship in the muscles around the shoulder, especially the shoulder abductors.  

The scapulohumeral rhythm allows us to have full ROM at the shoulder. The coordination between scapular and humeral movements is especially significant in movement of the arm above shoulder level. If a client is unable to reach above 90°, it is likely due to restricted movement of the scapula at the ST joint. This would throw off the scapulohumeral rhythm and ROM at the shoulder would decrease. The disharmony will cause friction at the glenohumeral joint. It is expected a client may feel pain in the shoulder due to impingement and damage to structures in the subacromial space.