Scapulohumeral Rhythm

Scapulohumeral rhythm is the relationship of movement between the scapula and the humerus. The ratio of movement is for every 3 degrees of shoulder movement, 1 degree of movement is at the scapulothoracic (ST) joint and 2 degrees from the glenohumeral (GH) joint. 

This rhythm is important because it allows for full range of motion at the shoulder. It does this by permitting good length-tension relationships. By doing this, it decreases the shear forces on the shoulder. We use our shoulder a lot for our ADL activities. The scapulohumeral rhythm gives the shoulder flexibility it needs to perform functions. As clinicians, we also need to know proper and improper scapulohumeral rhythm to recognize potential problems in clients. Lastly, this rhythm prevents impingement of the rotator cuff muscles. 

So to recap: it would be impossible for our shoulder to move without the scapulohumeral rhythm because our humerus would be detached from the glenoid fossa.