Our last blog post used a video to illustrate shoulder kinematics in 3D and reviewed how to externally rotate the humerus to protect against impingement. This week we look at the scapular motion on the ribcage and the role of the lower third of the trapezius in drawing the shoulders away from the neck. This motion is called scapular depression, and it is frequently used in yoga, especially when the arms are overhead. Scapular depression helps to maintain freedom of movement in the cervical spine, either to lift the head and look up (in Urdhva Hastasana) or to relax the head down (as in Dog Pose).
When you raise the arms overhead, the scapulae elevate, protract, and rotate. This is through the action of several muscles, including the upper trapezius and the levator scapulae. Scapular rotation occurs through sequential actions of the upper, middle, and lower thirds of the trapezius and the serratus anterior. Protraction is mainly through the work of the serratus anterior.