Scapulohumeral Rhythm

Full shoulder elevation requires the coordinated movement of the scapulothoracic movement and glenohumeral movement, called the scapulohumeral rhythm. During shoulder elevation, the first 30 degrees is considered the setting phase. At this point, the movement is primarily glenohumeral. After the first 30 degrees, the glenohumeral and scapulothoracic begin to move at the same time. The ratio of glenohumeral movement to scapulothoracic movement is 2:1.

The scapulohumeral rhythm preserves the length-tension relationships of the glenohumeral muscles; the muscles can sustain their force production throughout ROM because the scapula’s upward rotation keeps the muscles from shortening as much. Also, the synchronous movement of the humerus and the scapula during shoulder elevation limits relative movement between the two bones, preventing impingement between the humerus and acromion.

Any change in the position of the scapula in relation to the humerus will cause scapulohumeral rhythm disturbance (or dysfunction), which can contribute to shoulder impingement, rotator cuff pathology, winging of the scapula, and more shoulder instability. This type of dysfunction can cause a significant decrease in shoulder ROM in all the planes; the study of scapulohumeral rhythm is an important part of examining the shoulder.


Sources:

https://ouhsc.edu/bserdac/dthompso/web/namics/scapryme.htm

https://boneandspine.com/normal-scapulohumeral-rhythm/

https://handtherapyacademy.com/treatments/increasing-shoulder-range-of-motion-by-improving-scapulohumeral-rhythm/