Improving Posture: Don’t Get Trapped in Internal Rotator Dominance

In our computer-dominated society, poor posture is increasingly common. And while the usual recommendation is to simply ‘stand straight,’ changing posture habits is just not that easy.

Poor posture typically results from a combination of cascading, dysfunctional elements acting on our musculoskeletal system. This dysfunction is often exacerbated 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 from the upper arm and shoulder transmits an undesirable ‘pulling’ force onto the shoulder blades. This ultimately draws the shoulder blades forward, leading to inhibition and weakening of the musculature needed to counter dominant internal shoulder rotation. 

To improve posture and increase structural balance, it’s useful to get to know the various internal rotators to gain a better sense of these tension imbalances.

Pectoralis major – this powerhouse 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 collarbone 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). It 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). The teres major comes just off the shoulder blade and attaches very close to the same insertion as the latissimus dorsi (at the upper arm). 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 four rotator cuff muscles responsible for stabilizing and supporting the head of the arm bone in the shoulder socket, the subscapularis runs from the inside of the shoulder blade and connects onto the front of the arm bone. Besides shoulder socket stabilization, the line of pull from its contraction facilitates adduction of the arm bone and 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 internally rotating, and shoulder blades being drawn forward?

With simple changes and additions to our work and home life, we can prevent our bodies from having poor posture. By acknowledging these tendencies towards tension imbalances and structural disadvantages, we can slowly change our habits and tendencies, making it possible to ‘stand straight’ with ease.

Reprinted with permission from www.kregweiss.ca

Kreg Weiss, BHKin, is a certified hatha yoga teacher, international presenter and kinesiologist (exercise science).  All of his classes integrate a purposeful, meditative quality to allow for an experience of connection and reflection while the body explores expansion and renewal. With a background as a fitness trainer and athlete, Kreg has been teaching yoga since 2002 and complements his teaching practice with additional studies in Kinesiology and Health Sciences at the University of British Columbia. Through integrity-driven classes, Kreg aims to provide students with the tools to pursue a unique, confident practice where asanas, pranayama, and meditation interact collectively to rejuvenate and heal the body and mind.