The shoulder girdle is composed of the clavicle (collarbone) and the scapula. The placement of the scapula (and the shoulder girdle as a whole picture) affects the posture, and strength and mobility of the the arm movements and the spinal motions. When the shoulder girdle is properly placed in the neutral position, the socket will be stable so that all the muscles around the shoulder girdle can move in harmony and the core power can transmit to the arms efficiently to express its strength and mobility.
Of course the power of the movements is related to the pelvic girdle and the lower limbs, but in this post, I'd like to focus on the shoulder girdle.
The scapula engages in 6 types of motion, which allow for full-functional upper extremity movement including protraction, retraction, elevation, depression, upward rotation, and downward rotation. Through these six motions, the scapula allows full function of the shoulder joint, one of the most mobile and versatile joints in the human body.
Now, I'd like to address the neutral, stationary position of the scapula.
My cue will be "down-in-forward", 3 directional elements in one position.
First, you drop the scapula down, and pull it in, and push it forward. It sounds simple, yet what you're engaging, where you are initiating from, and the direction and the angle of it matters. Several muscles plays a role in the different position in the scapula, but I'll address below, certain muscle to focus on.
Downwards (depression);
The depression is accomplished by the action of the Latissimus Dorsi, Serratus Anterior, Pectoralis Major and Minor and Trapezius.
And I want to focus on Trapezius Lower Fibers which helps to depress the scapula, as well as helps upper fibers upwardly rotates the scapula. Lower fibers of the trapezius arise from spinous processes of the thoracic vertebrae (T4–T12). From this origin they proceed upward and laterally to converge near the scapula and end in an aponeurosis, which glides over the smooth triangular surface on the medial end of the spine, to be inserted into a tubercle at the apex of this smooth triangular surface.
Activation of lower fibers helps to stabilize the scapula during overhead movements. When the lower fibers are weak, the upper fibers engage more often than they should. When we are able to focus on isolating those fibers, especially lower fibers, then finally upper fibers can take a break and we don't get too tight neck and upper shoulders.
Inwards (retraction);
Retraction is accomplished by the action of the trapezius, Rhomboids, and Latissimus Dorsi. To move from deep layer of the muscles which has direct connection to the scapula bone and the spine (plus it's relating to the deep back arm line of fascia), I want to focus on engaging Rhomboids. Rhomboid major and minor originating on the nuchal ligaments and spinous processes C7-T5 and inserts into medium border of the scapula.
Forwards (protraction)
Protraction is accomplished by the action of the Serratus Anterior, Pectoralis Major, and Minor muscles. Serratus Anterior originates from the upper eight or nine ribs, from this wide origine, the fibers wrap around the thorax and underneath the scapula to be inserted into the vertebral border of the scapula.
Stand straight and engage those three muscle to stabilize the scapula in the back, and you would feel chest will be more open and lifted. However, as you keep the placement of the shoulder girdle, you'll need to drop (close or soften) the front ribcage towards the pubic bone to to bring the head slightly forward to lengthen the neck, and also to avoid compression of the lower back. Then the spine could be effortlessly elongated and you'll feel tall!
These images are from Muscles, Merves and Movement in Human Occupation by Ian R. McMillan & Gail Carin-Levy
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