The Disadvantage of Our Internal Rotators

Poor posture is often a combination of cascading, dysfunctional elements acting on our musculoskeletal system.  This dysfunction is not helped by the fact we have a strong tendency towards a dominance of our internal rotators of the humerus (upper arm bone).  As muscle tension imbalances set in across the shoulders and upper arms, the dominance of internal rotation places dragging tension onto the shoulder blades.  This ultimately draws the shoulder blades forward that leads to inhibition and weakening of the musculature needed to counter dominant internal shoulder rotation.  Let’s look at all the various internal rotators to gain a better sense of these tension imbalances.

Pectoralis Major – this power house chest muscle runs from the collar bone, chest bone, and ribs to connect into the top, front aspect of the upper arm bone (humerus).  Besides pulling the arm bone into the body (adduction), the pectoralis major has a significant internal rotation action on the humerus.

Anterior Deltoid – traveling from the collar bone and partly from the shoulder blade (acromion process), the anterior deltoid is responsible for flexing the shoulder (lifting the arm bone forward) and abduction (IF the arm bone is externally rotated), but also has a strong internal rotation component.

Latissimus Dorsi (and Teres Major) – another powerhouse muscle running from the hip crest, spinous processes of the vertebra, and ribs, this large back muscle comes from inside the arm to attach on the front, inside aspect of the upper arm (similar location to the Pectoralis Major).  Coming just off the shoulder blade and attaching very close to the same insertion as the Latissimus Dorsi (at the upper arm) is the Teres Major.  Both of these muscles play a major role in extending the shoulder (or bringing the arm bone back down into anatomical position from a flexed state).  Because of their line of insertion at the upper arm, these muscles also contribute to internal rotation of the humerus.

Subscapularis – one of our 4 rotator cuff muscles responsible for stabilizing and supporting the head of the arm bone in the shoulder socket, the Subscapularis runs from the inside (anterior) aspect of the shoulder blade and connects onto the anterior aspect of the arm bone.  Besides shoulder socket stabilization, the line of pull from its’ contraction facilitates adduction of the arm bone and clearly also internal rotation.

Our body has a set of external rotators of the humerus: Posterior Deltoid, Infraspinatus, Teres Minor.  When we compare the internal rotators to the external rotators, it appears that the external rotators are at a disadvantage in creating a balanced muscle tension relationship against the internal rotators.  Compound this structural disadvantage with postural imbalances from work, home, physical activity, health, and injuries, and we clearly see how the internal rotators can overwhelm the external rotators.  How much of our day is chronically spent with the arms forward (shoulder flexion), arm bones internal rotating, and shoulder blades being drawn forward?

By acknowledging these tendencies towards tension imbalances and structural disadvantages, we can integrate more mindful approaches to our exercise and yoga practices as well as bring more awareness to the need to avoid poor habitual lifestyle patterns throughout the day.  How can we change the design and sequencing of our yoga flows to more effectively restore tension balance and a harmonious relationship across our musculoskeletal system?  What changes and additions to our work and home life can we make to prevent the body from settling into a dysfunctional adaption state and instead help the body memorize postures that retain fluid space?