Importance of Scapulohumeral Rhythm

When you think of reaching up to the top shelf of your cabinet to get your box of cereal you may not be thinking of what all is happening within your body to make that movement possible. While you may feel as if you’re simply lifting your arm up, you should keep in mind that instead the whole shoulder complex: clavicle, scapula, humerus, and the joints in between, are having to shift in order perform this motion. The scapulohumeral rhythm plays a very vital role when it comes to making this movement, and many other movements of the upper extremity. So, what is scapulohumeral rhythm? 

Scapulohumeral rhythm is the ratio of movement between the scapula and the humerus.

And, why exactly is it important? 

Well, scapulohumeral rhythm ensures that our movements are coordinated, and in-sync. In order for this to happen, for every 3 degrees the shoulder moves, 1 degree is produced at the scapulothoracic joint and 2 degrees are produced at the glenohumeral joint. If this ratio is thrown off, it can result in limited shoulder range of motion. Scapulohumeral rhythm also helps maintain alignment of the head of the humerus in the glenoid cavity to be able to follow through a movement without it just sliding right out (ouch!). To add to that, it prevents another painful scenario of subacromial impingement, by limiting the movement between the glenoid fossa of the scapula and the head of the humerus, the space is able to stay open. Lastly, scapulohumeral rhythm ensures that the length/tension of the deltoid is able to shorten as much as it does for contracting to full extent.