October 25, 2011

A Response to David Keil’s Anatomy of Chaturanga.

I recently caught up with David Keil’s Yoga Anatomy articles and have been inspired to digress upon one of my favorite discussions.

The human form contains an infinite expression of both scientific observation and our own personal experience of physical sensation. The depth of our knowledge is perpetually growing and multiple branches of highly specialized fields of practice continue to emerge. But at the end of the day we are still left with an overwhelming sense of awe for how this thing called Life really works.

I concur with David’s post regarding chaturanga dandasana and the shoulder because we are obviously observing the same human form. His review of the skeletal and functional muscular anatomy regarding chaturanga is spot-on from my perspective. David and I share many of the same references, such as                    I. A. Kapandji MD, who is basically the Patanjali of anatomy.

Maybe it seems like a contradiction to write a response to someone’s article if you agree with it, but there are a few additions that offer a profound comprehension of the shoulder and are worth mentioning. These can become immediately applicable to a teacher’s practice.

First, no discussion of the shoulder complex is complete without mentioning the rotation of humerus that is created by the convex elliptical shape of the humeral head and the shallow concavity of the glenoid surface.

This concave/convex relationship is described as arthrokinematics, the science of how two joint surfaces interact. The study of arthrokinematics precedes the study of the relationship between muscles and joints. It’s like how chemistry precedes biology. It’s foundational.

So what is the shoulder actually doing during chaturanga? When the body is suspended above the floor, the muscles of the shoulder are performing a sustained isometric (no movement) contraction. The isometric contraction is holding the Gleno-humeral joint in very close approximation to neutral. That’s right, neutral. That means the “shape” of the gleno-humeral joint in chaturanga is the same as in mountain pose.

David says, “when we look at a movement like chaturanga, we are not moving out of the normal range of motion of the shoulder joint.” While his comment about chaturanga “not exceeding the normal range of motion” is physiologically the same as close to neutral, it is contextually important to appreciate the specificity of the latter.

The shoulder has the most range of motion (ROM) of any joint in the body, so it’s actually pretty hard to exceed its ROM without stressing the ligament capsule and subluxating the joint. Neutral shoulder is an ideal concept to apply here because we can assess shoulder stability before we assess strength simply by observing the shoulder presentation in mountain pose.

The real relationship between asana and injury begins with one vital aspect—how the body is aligned during the pose that preceded it. So you can probably trace an injury all the way back to mountain and everything else that showed up on the mat that day too. Which may be a good place to start assessing if you want to be one of those yoga teachers who can custom-design a practice based on a student’s physical presentation.

So let’s start from plank where the shoulder is flexed at 90 degrees. The body moves down towards the floor into chaturanga via extension of the shoulder. Remember, the head of the humerus is a convex ellipse that glides along the shallow concave ellipse of the glenoid fossa. The curve at this surface causes the trunk to slightly shift toward the head through the first half of the drop. Through the second half, as the head of the humerus is curving back down the opposite side of the ellipse, the body will shift back toward the feet again. It’s very subtle but easily experienced when you know what to look for.

The head of the humerus is not only elliptical, but it’s constantly changing the axis at which the humerus is rotating. During extension the elliptical head is spinning anterior (forward) and medial (toward the midline). While the humeral head is spinning, it is also sliding across the surface of the glenoid fossa. Think of it like a top spinning but also moving across the surface of a table. It’s multi-dimensional.

So a possible argument on the “pesky scapula placement debate” would simply be to place the scapula in an ideal position so the humerus can glide with the least resistance about the glenoid surface.

The position of the scapula determines the function of the humerus based on these gliding surfaces. A protracted scapula changes the surface interaction and increases resistance during extension. A retracted scapula increases the resistance during flexion. Neutral scapula offers the best biomechanical advantage for a moving humerus. So get on the floor and try moving from plank into chaturanga—first do it with excessive scapular protraction, then retraction. Then find neutral and notice the smooth glide as your elbows hug the ribs.

Understanding the relationship of joint kinematics is the first step to understanding neuromuscular patterns. How the body “patterns,” a term David mentioned, in transition from one pose to the next requires a synergistic coordination of multiple muscles.

I refer to this stabilization simply as “the muscles playing together nicely.”

And if there is one muscle that often refuses to show up and play nicely with the other shoulder stabilizers, it would be the levator scapulae. While its name suggests its function (scapular elevator), the true importance of the levator is not the action on the shoulder, it’s the proximal attachment to the cervical spine (C1-4). It is a primary instigator with 90% of the shoulder and neck injuries I see in yoga practitioners.

(Levator Scapula)

David does a good job explaining how a misaligned shoulder can cause compensatory movements in the elbow, wrist and low back. But the most critical aspect of the shoulder complex are its muscular attachments to the cervical and thoracic spine.

Again, I couldn’t agree more with David who recommends, “If you’re experiencing shoulder pain or have students who are, take a moment and observe them. Don’t just try to make them do it differently because it doesn’t look right, look at the bigger picture”—which for me would be to start by observing the student in mountain pose.

Shoulder Posture Evaluation

Observing from the front.

1. Are the shoulders even in height? If not, trapezius or levator may be weak/fatigued.

2. Is the angle between the neck and the slope of the shoulder even on both sides?Asymmetrical head tilting suggests a more advanced/chronic condition of the spine and shoulder.

3. Is the nose directly over the sternum or shifted to one side? And is the head rotated?  Both abnormalities suggest a shift of the cervical spine and will affect shoulder function.

4. Are the hands equidistant from the body? One hand forward indicates a rotation of the thoracic spine, which changes how the shoulders hang. If one hand is further away from the body then the shoulders are not stacked directly over the hips, indicating a shift in the thoracic or lumbar spine.

5. Are the hands rotated? Internal and external rotation of the hand may be secondary to rotation of the shoulder.

Observing from the side.

1. Are the shoulders depressed and slumped forward?

2. Is the head forward?  The ear hole should be directly over the middle of the shoulder.

Any displacement of the head over the shoulder indicates a decreased lordotic curve in the cervical spine. It also indicates a levator that is elongated, weak and tired of being pulled back and forth between spine and shoulder, and if you put it in a challenge pose like chaturanga—it may just snap.

When levator gets cranky, it jacks the scapula way up, which not only yanks on the spine all day long, but also increases susceptibility to impingement syndromes and bursitis. Long term impingement leads to osteophytic formation (bone spurring), mostly occurring in people over 50. Although, I’ve seen bone spurs in a 20 year old shoulder too.

The presentation of neutral posture allows you to evaluate your student’s ability to perform asana long before they ever hit the mat. Any deviation from normal posture here will inevitably result in abnormal alignment during postures that requires sustained dynamic stabilization, such as chaturanga.


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