Scapulohumeral Rhythm

The scapulohumeral rhythm is the ratio of movement between the humerus and scapula during glenohumeral movement. This rhythm is relevant because the muscles acting upon the glenohumeral joint cannot be shortened as much as they can without the upward rotation of the scapula. Since the scapula moves in the scapulohumeral rhythm, it helps the glenoid fossa maintain an ample position for all movements of the head of the hummers. This rhythm also maintains the tension length relationship of the upper shoulder muscles. Another reason that this rhythm is relevant, is because it maintains the subacromial space which is between the top of the humerus and the acromion. Since this space is maintained it prevents impingement of the muscles and the subacromial bursa within this space. This rhythm is a ratio of movement is 1 to 2. For every 1 degree of movement at the scapulothoracic joint, there are 2 degrees of movement at the glenohumeral joint. This is important to know when you are measuring the range of motion at the glenohumeral joint because you have to take into account the movement that the scapula upward rotation is responsible for. For example, if the client has a total ROM of 150 degrees for shoulder flexion, 50 degrees of that will be from scapula upward rotation and 100 degrees would be from the glenohumeral joint.