Capsular Constraint Mechanism
Why it might pinch when you rotate your joints.
Photo by Otto Norin on Unsplash
I sat down at a Functional Range Conditioning seminar in late November 2017 and heard a concept that fundamentally changed the trajectory of my career.
If your capsule is restricted you can’t rotate, you don’t have a joint.
It took me some time to truly understand what Dr. Spina meant by this. In time as I went about training humans and assessing joints, it clicked the more I learned about the FRS system.
The statement above doesn’t mean you’re having some arthroplasty, rather your joint doesn’t have access to all its degrees of freedom.
In plain English: You’re lacking control in the range of motion your joint should have available to it.
Capsular Constraint Mechanism
Let's use your shoulder joint.
The capsular constraint mechanism states that a tight capsule around the humeral head shifts the direction opposite to the tightness being produced(1). An analogy that helped me understand this is that the joint capsule is like a stress ball that encloses the space between two bones, so as you rotate in one direction, the opposite side needs to accommodate for that.
Applying this to a real-world example. Let's say you’re getting ready to back squat and you set your upper traps under the metal barbell and grab it on both sides as you externally rotate underneath only to feel this pinching sensation on the back side of your shoulder.
“Must just be tight back there”, so you grab your foam roller or lacrosse ball. You roll on the thing for a few minutes and your posterior shoulder feels “looser”. You get back under that bar, pinch! It’s because you’re chasing the symptom and not the root cause.
This makes sense when you look at a dissection of the shoulder, your rotator cuff tendons all blend into the joint capsule. (2) If we lose the ability to rotate, there’s a solid chance your “tight muscles” can’t be stretched or massaged because your problem isn’t only muscular, it’s capsular. When the capsule lacks the space to accommodate the movement, you get that pinching sensation.
It’s all in your brain…kind of
Why does this happen? A little anatomy to help explain this.
Photo by CHUTTERSNAP on Unsplash
In your shoulder, you have your labrum and the next piece of tissue is your joint capsule. The capsule contains mechanoreceptors that sense the world around you and sends that information up to your brain.
In general, sensory information is relayed to an interneuron at the spinal cord before it is either remedied through a reflex or sent up to your brain where it’s sorted to the proper areas before kicking the signal back down to your muscles.
We have 4 types of mechanoreceptors that relay information about what’s going on. The joint capsule contains type 1 and 2 receptors.
Type 2 receptors (Pacinian-like or Krause corpuscles) skip that step at the interneuron and travel right up the spinal cord and report directly to the brain. This means your capsule senses movement long before your muscles do!
Now, why is this important?
Well, if we understand that mechanoreceptors sense information about our movements and our movements aren’t very good. Then the information relayed to the brain is that of aberrant movement. Over time, the nervous system interprets this as your new normal and you end up with poor length-tension relationships for your muscles. (3)
This ultimately leads to changes in your joint capsule space (not good) because based on the information your movement gave the brain, it interpreted that you didn’t need all the available workspace.
So, if we know that joint capsules will ultimately restrict our movements and the joint capsule of the shoulder is intimately tied to the rotator cuff, shouldn’t you maintain rotation as much as you can? (the answer is yes, you should)
So what about that pinchy shoulder?
This applies to both internal and external rotation, assuming you don’t have some more serious injury like a labrum tear or ligamentous sprain.
When you rotate your shoulder externally, you will inevitably reach that pinch point. Back out of that position a little bit.
Find an object and rotate externally and try ramping up isometrically to as strong of a contract as you can maintain. Hold for about 10 seconds.
When you externally rotate further, I’m willing to be your shoulder magically has both more ROM and no pinch, at least not at the position you initially felt that.
Repeat until you get to your desired end range.
Conceptually, the same process applies to internal rotation.
Long-term-wise, training with the intent to maintain end-range rotation training is key to keeping joints healthy.
References:
Kim Y, Lee G. Immediate Effects of Angular Joint Mobilization (a New Concept of Joint Mobilization) on Pain, Range of Motion, and Disability in a Patient with Shoulder Adhesive Capsulitis: A Case Report. American Journal of Case Reports. 2017 Feb 10;18:148–56.
Witherspoon JW, Smirnova IV, McIff TE. Neuroanatomical distribution of mechanoreceptors in the human cadaveric shoulder capsule and labrum. Journal of Anatomy. 2014 Jul 9;225(3):337–45.
Ganguly J, Kulshreshtha D, Almotiri M, Jog M. Muscle Tone Physiology and Abnormalities. Toxins. 2021 Apr 16;13(4):282.