It's All About The Rhythm

For the shoulder to have the greatest ROM the scapulohumeral rhythm is very important. Scapulohumeral rhythm is the muscle interactions within the scapula and humerus.  For every 3 degrees of shoulder movement, there is 1 degree of scapular movement and 2 degrees of humeral movement. This rhythm and its ratio is very important in the synchronization of the scapula and humerus movements.  The rhythm also helps maintain the subacromial space within the glenohumeral joint. This rhythm also allows for good length tension relationships to prevent active insufficiency. The two joints congruency results in decreased shear forces of the humerus in the glenoid fossa.  When the motion is distributed between the humerus and glenoid fossa it allows for stability, if the ROM is large there is a chance for instability. The scapulohumeral rhythm is important for therapist when looking at the overall muscle and shoulder joint functions. A poor rhythm could also cause shoulder impingements in the rotator cuff like bone spurs, humeral and scapular movement dysfunction, and changes in the acromion shape.