What does the shoulder blade have to do with our shoulder moving?
Scapulohumeral rhythm: What is it?
Refers to the coordination between the shoulder blade (scapula – “scapulo”) and the humerus (the bone that runs between the shoulder and elbow – “humeral”) during shoulder movements. It represents the ratio of movement that is done by the shoulder blade relative to the amount of movement done by the humerus when lifting the arm.
What muscles are involved?
Movement of the scapula is aided by the serratus anterior, and the upper and lower fibres of the trapezius. Whereas, movement of the humerus is initiated by the rotator cuff muscles which includes the supraspinatus, infraspinatus, teres major, teres minor, and subscapularis.
Image 1: Muscles Rotator Cuff (ref below)
The action of raising the arm up and to the side (abduction) involves a 2:1 ratio of movement from the humerus relative to the scapula. So on an average abduction of 180 degrees – 120 degrees comes from the movement of the humerus while the remaining 60 degrees is achieved from the scapula.
What happens when the ratio is abnormal?
Abnormalities in this ratio is called scapular dyskinesia – which means an impairment in the scapular movement. When the scapula is moving abnormally it can lead to pinching of various structures within the shoulder causing pain when moving the arm.
What can we do?
When shoulder pain is the result of scapular dyskinesia the goals of treatment may include strengthening, stretching, and ultimately promoting proper scapulohumeral rhythm. Your therapist may test to see which muscles may be weakened or tight, assess for incorrect postures, and create individualized exercise prescriptions that allow for the restoration of proper scapulohumeral rhythm.
Image 1: File: Muscles Rotator Cuff.jpg. (2011, August 29). Physiopedia, . Retrieved 18:18, January 28, 2019 from https://www.physio-pedia.com/index.php?title=File:Muscles_Rotator_Cuff.jpg&oldid=44396.