The shoulder girdle in upright beings is very vulnerable to dysfunction. It is not as stable as the pelvis, nor is it as low to the ground which makes it easier for trouble to develop. In the past week I have been writing about a whole mess of muscles that are designed to work together to stabilize the shoulder-blade on the back when we perform tasks with the upper body.
Serratus anterior is the last of the four main muscles that I that I think work most to accomplish the difficult task of stabilization. The pectoralis minor, the lower trapezius, the rhomboids and serratus anterior are all trying to work together to keep the shoulder-blade in place when the body is called upon to do a great many actions.
From the yoga perspective it is easiest to see this when lowering from plank to the floor. The whole upper body wants to remain stable in this action but weakness in any of these muscles throws off the others. There is a post coming about this exact dilemma but I wanted to introduce all of the actors in the drama first.
Serratus anterior connects to the first nine ribs (from the top down). It wraps towards the back around the ribcage behind the shoulder-blade, to connects to the medial (Inner) spine of the shoulder-blade.
The muscle of the previous couple of posts, the rhomboids, also attaches to the medial spine of the shoulder-blade at the front of the shoulder-blade and then moves to the spine. These muscles work with/against each other to stabilize the shoulder-blade.
The serratus anterior can be broken down into three sections with different functions. All of the sections pull the shoulder-blade towards the front of the body and also help with breathing. The top and bottom sections work against each other to assist in raising and lowering in the arms.
In the same way that I described the latissimus dorsi as the swinging from the trees muscle, the serratus is the punching muscle as it draws the shoulder-blade forward as the arm comes around to punch.