“. . . 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



Saturday, April 16, 2011

Shoulder Kinematics in Yoga, Part I

The shoulder is the most mobile joint in the body. It is a combination of several articulations: the glenohumeral, scapulothoracic, sternoclavicular, and acromioclavicular joints (click here to see these). Each of these contributes to shoulder and arm movement via a process known as joint “coupling.” For example, when you raise the arms over the head in Urdhva Hastasana, the clavicle pivots on the sternum (breastbone), the scapula rotates on the chest wall, and the head of the humerus moves within the shoulder joint. All of these work together simultaneously in what is known as scapulohumeral rhythm. In general, 60 degrees of this action comes from movement of the shoulder blade on the chest wall (scapulothoracic motion) and 120 degrees from the ball and socket of the shoulder (glenohumeral motion). During this process, the clavicle rotates on its long axis approximately 25 degrees and the humerus externally rotates about 45 degrees. Scapulohumeral rhythm is illustrated in the video below, with a breakdown of scapulo-thoracic and gleno-humeral contributions to the entire movement.



So we can see that the shoulder is a complex structure, with many factors contributing to movement, or potentially restricting it. It’s easier to understand a complex structure by breaking it down into its component parts and then reconstructing them into the whole. This gives a new understanding of their function. For the shoulder, we’ll begin by focusing on the skeletal anatomy of the glenohumeral joint.

Here’s the Anatomy . . .

The glenohumeral joint comprises the humeral head and the glenoid fossa of the scapula, which together form a shallow ball and socket joint. The proximal humerus also has two protuberances to which the muscles of the rotator cuff attach. These are the greater and lesser tuberosities. To see the anatomy of the rotator cuff, click here.

Another important structure of the scapula is the acromion process. This shelf-like projection of bone forms a roof over the top of the glenohumeral joint. It is also the attachment site for the deltoid and part of the trapezius. The subacromial bursa lies between the acromion and the proximal humerus (the humeral head and the greater tuberosity). It is a sac-like structure that facilitates gliding of the greater tuberosity and tendons of the supraspinatus and infraspinatus muscles on the undersurface of the acromion. Additionally, there are the muscles that attach to, move and stabilize the scapula, namely the rhomboids, trapezius, serratus anterior and levator scapulae.

subacromial bursa of the shoulder
                               The greater tuberosity (1)                                             The subacromial bursa (2) and acromion process (3)

This Brings Us To Subacromial Impingement . . .

When the arm is raised, either to the side or in front of the body, the greater tuberosity can “impinge” on the undersurface of the acromion, compressing the subacromial bursa and irritating the supraspinatus tendon. This is more likely to happen if the humerus is internally rotated. Externally rotating the upper arm bone draws the greater tuberosity out of the way of the acromion and aids to prevent impingement. The acromion comes in several different shapes, ranging from flat to curved. Curved acromions have been associated with a greater incidence of subacromial impingement.

shoulder impingement
The first image shows impingement of the subacromial bursa with the humerus internally rotated.
The second image illustrates external rotation of the humeral head preventing impingement 


So What Does This Have To Do With Yoga . . .

The question has been raised as to whether persons with a curved acromion are limited in their ability to perform certain asanas. For example, the inference that appears to have entered the yogic nomenclature is that if you cannot bring your arms vertical in a pose like Urdhva Dhanurasana, you must have a curved (not a flat) acromion. This is generally incorrect. First, it is well-established through many studies that a curved acromion does not affect the functional range of motion of a healthy shoulder. People with curved acromions can raise their arms overhead just as far as those with a flat acromion. Second, it is impossible to tell the shape of someone’s acromion process by observing them in a yoga pose. Acromial morphology is something that is determined with a specialized X-ray.

So to answer the question, “In a healthy shoulder, do curved acromions affect the ability to raise your arms overhead in a pose such as Urdhva Dhanurasana?” The answer is that this is unlikely. The scapula rotates to bring the acromion out of the way of the humerus for much of the range of movement.  There are many other more likely explanations for this limitation, including tightness in various muscles or the capsule and ligaments about the shoulder as well as inflexibility in the thorax/ribcage.

How Do We Prevent Impingement?

externally rotate the shoulders to avoid impingement

Now let’s consider how this relates to actual practice. Particularly in Vinyasa, there is a tendency to do the same movement many times, which can lead to repetitive stress injury, such as inflammation of the subacromial bursa and supraspinatus tendon—“rotator cuff syndrome” in the orthopedic nomenclature. You can help to avoid this by engaging the infraspinatus and teres minor muscles and, to a lesser extent, the deltoid. These muscles act to externally rotate the humerus and bring the greater tuberosity away from the undersurface of the acromion. We illustrate this movement here in Urdhva Hastasana. To read about the anatomy and to see this concept in action in Dog Pose and Full Arm Balance, click here.

Thanks for checking in. We’ll see you for the next post when we go over the muscles that move and stabilize the scapula. Be sure to download volume two of our free interactive eBookAlso, don’t forget to tell your friends about our blog and to visit us on Facebook for your free chakra poster.

Namasté,

Ray and Chris 

17 comments:

  1. absolutely love that 29 second video, made things so much clearer for me

    i think i even have internal and external rotation of the humerus down ;-)

    thanks so much

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  2. Thanks Adan--good to hear from you. All the Best~Ray

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  3. I think this video is very helpful. Nama

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  4. Thanks Johnny--good to hear~Ray

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  5. There are a lot of benefits when it comes to practicing yoga. This is a good demonstration of its kinematics.

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  6. Thank you so much for this video, I will be forwarding to my students.

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    1. Thank you, Brenda--I'm delighted you enjoyed the video. It was fun to produce as well. All the best with your teaching~Ray

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  7. Thank you it is so good to see what is happening inside the shoulder, I have tendinosis of the supraspinatus, now almost 6 months since it was diagnosed, it is slowly better but still not cured, any recommendations for helping it heal? I am doing a modified practice to not bear weight or lift the arm all the way up.

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    1. Hi Rocio--glad to hear your tendinosis is improving--stay with it, work with strengthening the cuff and periscapular muscles as well as mobility. Ray

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  8. I'm incredibly grateful to study this article this week having come to point in my practice where my body has forced me to finally address the vast difference in range of motion between my right and left shoulders.

    A painful pinching in my right shoulder has so long been a part of my practice that I had given up hope of asanas requiring a great range of shoulder motion like kapotasana or dwi pada viparita dandasana. But a recent couple of corrections to adho mukha svanasana from two excellent teachers drastically transformed my shoulder placement in the pose which then of course revealed misalignment and over-extension habits in so many other asanas. The great beauty of the interconnectedness in this practice...!

    This article as well as your gomukhasana for stiff shoulders instruction is the icing on the cake of this correction. I believe now I'm on a correct path of shoulder alignment and I'm so thrilled to know that I will indeed be able to transform something I thought might just be impossible for my musculoskeletal structure.

    I'm so grateful for your detailed instruction - thank you, thank you from the bottom of my heart.

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    1. Hi Monica,

      Many thanks for your comment--I'm delighted to hear that you enjoyed this article and that things are going well for your practice! All the Best~Ray

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  9. Somehow over the years I lost the forearm pronation. Instantly removed wrist pain that's been building up over the last year. Many thanks. :)

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    1. Thanks Eric--glad to hear your pain is improved. Cheers~Ray

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  10. It was such a pleasure to study about the biomechanics of the shoulders. So often, you read something and still can't quite understand how it relates to you or how to explain it your students. Thank you for creatively presenting the relevancy in the biology and the practice. I am enjoying it all.

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  11. Finally getting a chance to check out the website after the Oct workshop with you in Columbus. So much to read...Thanks again for all of your contributions and knowledge - it has helped me tremendously in my yoga practice, my yoga teaching, and especially in working with my massage therapy clients.

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  12. Thanks so much for this! The video really helped, and the details really help me to think of ways to 1) give clearer cues in class, and 2) tend to my own shoulder!

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