Scapulohumeral Rhythm

Hi All!

More educational ramblings to share... 

In teaching group exercise, and more frequently in Crossfit, I've experienced and seen many shoulder injuries. What may cause these injuries is weakness in the middle trapezius and serratus anterior. Most group classes and Crossfit include tons pushing and pressing movements without tons of pulling to counter balance all the anterior work. Even pull ups cannot address the lack pulling alone, but including seated rows, band rows from high and low angles, as well as scapular stabilization exercises can greatly reduce the risk of injury for group class and Crossfit participants. To further understand the shoulder joint, below is a description of the relationships between various parts of the shoulder and the muscles involved in upward rotation of the scapula, as well as the description of one shoulder condition that inhibits healthy movement patterns. 

Scapulohumeral rhythm describes the coupling of shoulder girdle movement with arm movement, Muscolino also states that the motion of the clavicle is also required; therefore perhaps a better name would be “scapuloclaviculohumeral rhythm” (2011). Two separate joint actions that must occur simultaneously are called coupled actions. In the case of the shoulder, only a small degree of movement can occur solely at the glenohurmeral (GH) joint, so when the shoulder moves, movement occurs between the clavicle of the shoulder girdle and the sternum at the sternoclavicular (SC) joint and between the scapula of the shoulder girdle and the rib cage at the Scapulocostal (ScC) joint. A scapular force couple is produced by the trapezius and serratus anterior muscles in upward rotation of the scapula (Donatelli, Ruivo, Thurner & Ibrahim, 2014). Upward rotation of the scapula occurs in arm elevation, for this movement to happen with a full range of motion the shoulder must be healthy.

Having the condition known as “frozen shoulder,” or adhesive capsulitis, may result in the failure of the scapular force couple because of pain and stiffness that can inhibit normal movement at the shoulder joint. Although the cause of frozen shoulder is unclear, it is characterized by the process of thickening and contracture of the capsule surrounding the shoulder joint (Soviero, Gucciardi, & Geraci, 2008). When a client is experiencing frozen shoulder their mobility will be greatly reduced, particularly in external rotation and overhead movements. The three muscles that are traditionally attributed as upward rotators are the upper trapezius, lower trapezius and serratus anterior. Due to the complexity of the shoulder joint, there are many conditions that may cause force couple failure, but frozen shoulder can be treated with low load stretching, end range tensile stress, and progressive loading (Donatelli, Ruivo, Thurner & Ibrahim, 2014). Most often frozen shoulder will be improved through treatment and then scapular motion can be reassessed to see if there are other factors inhibiting force coupling such as forward head posture, rounded shoulders or hyperkyhposis.

1) Muscolino, Joseph E. (2011). Kinesiology: The Skeletal System and Muscle Function.  St. Louis, MO. Mosby, Inc., an affiliate of Elsevier Inc.

2) Soviero, F., Gucciardi, S., & Geraci, A. (2008). THE FROZEN SHOULDER: UNKNOWN AND KNOWN KNOWNS. (English). Capsula Eburnea, 31-14.

3) Donatelli R, Ruivo R, Thurner M, Ibrahim M. Masterclass: New concepts in restoring shoulder elevation in a stiff and painful shoulder patient. Physical Therapy In Sport [serial online]. February 1, 2014;15:3-14. Available from: ScienceDirect, Ipswich, MA. Accessed October 23, 2014.