“. . . according to the Yoga Sutra (3.1), the term [Bandha] refers to the ‘binding’ of consciousness to a particular object or locus (desha), which is the very essence of concentration.”
Georg Feuerstein



Sunday, March 13, 2016

Shoulder Biomechanics, Part II: The Infraspinatus & Teres Minor Muscles


Hello Friends,

Welcome to the second of the four-part series on the shoulder joint. Last week I discussed the subscapularis muscle, which is the main shoulder internal rotator. Now we’re on to the antagonist muscles of the subscap, namely, the infraspinatus and teres minor. The infraspinatus arises in a trough below the scapular spine, hence its name (“infra” means below). The teres minor arises back part (dorsum) of the scapula along its outer (lateral) border. The infraspinatus and teres minor insert onto the back part of the greater tuberosity of the humerus, as shown in Figure 1. 

These muscles externally rotate the humerus, with the infraspinatus being the strongest external rotator of the joint. The infraspinatus and teres minor also function to stabilize the humeral head in the socket (glenoid).




Figure 1: The infraspinatus and teres minor muscles of the rotator cuff (the supraspinatus is the faded muscle on top).


The Force Couple


These muscles combine with the subscapularis at the front of the joint to form a “force couple”. In this manner, antagonist muscles (for rotation) become synergists (for stability). Therapy (and surgery) for rotator cuff pathology is directed towards restoring this force couple. Click here to read about concept of antagonist/ synergist combinations for the hip muscles in yoga. Click here for some cues to use this in Dandasana.
Figure 2 illustrates this biomechanical process. This view is looking down on the shoulder with the front of the joint towards the bottom of the page



Figure 2: The force couple between the infraspinatus and subscapularis muscles. This view is looking down on the shoulder with the front of the joint towards the bottom of the page.

Poses with the arms in reverse Namaste' stretch the infraspinatus and teres minor, as does Gomukhasana. Those of you who are more flexible may gently press the knife edge of the hand into the back to "load" the external rotators. Folks who are tighter may simply grasp the elbows or hands behind the back. Click here for more details and an animation of Gomukhasana stretching these muscles as well as a not so obvious cue for loading and using PNF for this stretch.

Figure 3: Stretching the infraspinatus and teres minor by internally rotating the shoulders in Parsvottanasana.


Externally rotating the shoulders in poses like Trikonasana (Triangle) can be used to activate the infraspinatus and teres minor. Figure 4 illustrates this, as well as the myofascial connection between these muscles and the muscles that retract the scapula, namely the trapezius and rhomboids.




Click here to take the rotator cuff quiz and test your knowledge!

Thanks for stopping by--I hope you're enjoying learning about biomechanical concepts like the force couple. Stay tuned for the next post when I'll go over the last muscle of the rotator cuff, the supraspinatus. Then I'll finish up with the relationship between the rotator cuff and the deltoids. By the end of this four-post series, you'll have a good understanding of the functional anatomy and biomechanics of the shoulder joint as applied to yoga. Click here to browse through the Bandha Yoga book series on anatomy, biomechanics and physiology for yoga.


All the Best,

Ray Long, MD

14 comments:

  1. Ray,
    Thanks for this article! It's very timely, as I've recently developed tendonitis of the tendons of one of those two muscles (going to see my Ortho this week). This was very educational.

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    1. Glad you enjoyed it, Kat. Good luck with the tendonitis. Best~Ray

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  2. This is very interesting info.thanks.

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  3. This is so helpful. I am especially interested in hearing about the relationship between these muscles and the deltoid. I have a few clients who are working to strengthen the RC, but the deltoid is aching, limiting range of motion.

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  4. Very interesting info, thank you very much!

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  5. Es muy interesante. Ideal para hacer las cosas bien y aprovechar al máximo cada movimiento y postura.

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  6. I had the same problem. But the deltoid was just referred pain. The issue was in my infra spinatus. Thanks Ray for your informative blog posts. I always learn something.

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  7. I have learned so much, simply and precisely what I need to pass on to and protect my students... On and off the mat! Thank you

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  8. Learning anatomy from you and my great yoga teacher Greg Anton, who first showed me your books, has intelligently informed my practice and continues to engage my interest and curiosity. I love you for your work and generosity. You are great teachers. On second try I aced the shoulder quiz! o we learn.

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  9. And your quiz comes to me five days before my shoulder surgery. I can now tell people that my force couple had a blow out but they will be getting back together! Thank you for the great articles and visuals.

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