the Scapulo-humeral Rhythm

I have been working on deep backbending for years, but the specifics of shoulder recruitment had not really occurred to me until Sarah Hatcher drove the point home. She strongly encourages working the chest after external rotation of the humeral head has been achieved in the initial stages of powering up the arms. She didn’t describe it this way. She used physical adjustment and cueing to get me on board with the movement.

The best Yoga teachers tend to have their own language for these subtleties and rarely get bogged down in anatomical jargon. Encouragingly, the analogies and cues often used by experienced Yoga teachers are almost always rooted in sound anatomical principles. Bioetensgrity shows us this holistic truth. Last year I found out for myself by dissecting a cadaver that Sarah’s instructions regarding the scapulo-humeral rhythm in backbending are indeed good science.

The words that follow are my humble findings, and if I can help you to better understand the rotator cuff anatomy then the job of this post is done. The playlist of videos in this post is showing my journey with setting up the upper and lower limb patterns for healthy backbending using props.

The scapulo-humeral rhythm describes the timing of movement at the gleno-humeral joint and scapulo-thoracic joints, in that order. During shoulder elevation, the first 30 degrees of movement occurs at the gleno-humeral joint. As I have seen on the cadaver, the joint capsule and bursa in which the humeral head is ensconced is sandwiched at its proximal surface against the inferior surface of the acromion and is thereby vulnerable to impingement unless the length-tension relationships of the gleno-humeral muscles (commonly called the rotator cuff) are maintained through healthy movement patterns. The crux of this “healthy movement” is to cinch down and then externally rotate the humeral head before abducting or loading the humerus.

This tiny, very specific movement is incredibly difficult to enact at first, but once I started to get it wired into my practice, my backbending technique was transformed. Sadly, years of destabilising my left shoulder through asymmetrical overloading tendencies has left me with an unstable left AC joint. These “little niggles” make deep asana a bit trickier, and you can check out my post on sore shoulder for more about how to adjust your chaturanga in case you’re suffering too. Alas, let us now focus on the good science of shoulder biomechanics toward finding maximum sukham, or ‘good space.’

The first step in deep backbending from a standing position is to reach your arms up overhead. As I have now seen on the cadaver, this ostensibly simple instruction is achieved only through a complex sequence of subtleties. The coordination of movements of the scapulae and humerus toward abducting the upper limbs the scapulo-humeral rhythm, is best considered once we have defined a few structures.

The scapulo-thoracic joint is not a bony articulation. Rather, this joint describes the relationship between the scapula and the thoracic cage, which is actually a sort of “jacket” of myofascial that should glide smoothly in a healthy subject. The glenoid fossa is the shallow “tee” found on the lateral aspect of the scapula where the “golf ball” of the humeral head articulates with the scapula at the gleno-humeral joint.

It is worth mentioning here that the glenoid is lined with a disc of articular cartilage known as the labrum, which can become damaged if shoulder joint instability worsens. In Yoga, the shoulder is especially vulnerable to destabilisation because of the tendency to load the joint before properly positioning the shoulder girdle relative to the soft tissues of the rotator cuff.

The shoulder girdle refers to the shoulder’s bony structure and consists of three bones: the clavicle, scapula and humerus. The rotator cuff is comprised of soft tissues and is usually defined by four muscles: supraspinatus, infraspinatus, teres minor, and subscapularis (SITS).

The rotator cuff stabilises the shoulder girdle, which is a shallow joint to allow for greater mobility. As such, the shoulder can be its own worst enemy because the bones present a shearing force on the common tendon of the rotator cuff that is threaded delicately between the humeral head and the roof of the acromion. The acromion process is a bony outcropping that articulates with the clavicle and provides the continuous attachment site for deltoids muscle and, ironically, also provides protection to the glenohumeral joint underneath.

Here we can see the delts have been faded to get a view of the highlighted supraspinatus muscle as the tendon passes in that subacromial space:

If a practitioner attempts to abduct the arms beyond this initial 30 degrees without having first externally rotated the head of the humerus, they are in danger of pinching the bursa and a tendon of the rotator cuff between the humeral head and the roof of the acromion. Performing this unhealthy rhythm repeatedly with force can inflame, fray, or possibly tear the tendon and result in chronic pain associated with impingement syndrome, which is one of the most common types of rotator cuff injuries.

Think of it this way. Who among us has not smashed a finger in the door jam at one point or another? My little sister, Mandy, still bears the scar on her nail bed and will happily relate the story of how her big sister’s taunts spurred a rampage which led to her chasing me throughout the day-care centre in a frenzied rage until – SLAM – the furore reached a crescendo and next thing I knew there was blood everywhere, and my sister is missing a chunk of her little finger. If you put a soft thing between 2 hard things and slam those hard things against one another, the soft thing will naturally be the one that pays the price. In the case of the shoulder joint attempting to perform Hasta Uttanasana, the hard things are parts of the shoulder girdle, and the soft thing in question are the muscles as they merge to form the vulnerable rotator cuff tendon. The pathology can develop from trauma in an instant or as a result of repetitive strain over a long period of time. In the case of repetitive strain, it is possible to reverse the sypmptoms but it takes a conscious effort to research and rehabilitate your rhythm.

In addition to first externally rotating the head of the humerus, there is another movement that can aid the preservation of the rotator cuff during abduction of the arms. Roger Cole, to whom I credit furthering my understanding of these concepts, calls it “cinching down.” I have heard other teachers instruct “plugging in” the humerus before coming into a backbend from the supine position. The intention is the same: we are looking for maximum sukham.

Good space, like good science, is a revelation of simplicity. When we pull the head of the humerus inferiorly away from the roof the acromion, there is a net increase of space between the two surfaces, which will aid the consequential external rotation, preparing the shoulder for the deltoids to perform their duties in abducting the joint through the rest of its range of motion without inadvertently shearing the soft tissues in the process. The cinching down action is primarily achieved by the infraspinatus and the teres minor.

Teres minor is particularly active during the downward pull of the humerus. As I have observed in dissection, this muscle lies inferior to infraspinatus on the scapula, and therefore its tendon runs at a more vertical angle on the posterior surface of the humeral head. Because of this more vertical aspect, the teres minor attaches to the greater tubercle of the humerus at an angle that not only externally rotates the humeral head during contraction, but also pulls it down.

This scenario is the crux of my recent revelation about the shoulder, which I have experienced first-hand in my own anatomy and have now seen in detail in the cadaver. I had the rare opportunity to actually pull on teres minor to produce the cinching down of the humeral head in the cadaver to observe this subtle but critical movement in the initial stages of the scapulohumeral rhythm.

Now that we have seen the importance of the cinching down and external rotation before full abduction of the humerus, it is interesting to note what can happen if we do not preserve the health of the rotator cuff. Impingement of the tendon can cause moderate to severe pain even at night, loss of motion and strength, and can result in the inability to abduct the arms. Destabilisation of the rotator cuff, as mentioned previously, can lead to degradation of the articular cartilage. Treatment protocol includes both surgical and nonsurgical interventions, and as usual we can be sure the best treatment is prevention. Put simply: find some good space, and linger there.

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