What are we doing in yin yoga?

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Bernie
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Joined: Sat Sep 23, 2006 2:25 am
Location: Vancouver

What are we doing in yin yoga?

Post by Bernie »

I recently received the following question:
  • I have a question re: what are we doing in yin yoga? I've been working with Chris Clancy and the biotensegrity model of the body the past year. According to the non-linear stress-strain curve of tendons, at only 8%, we enter the plastics zone - where the tissue will have micro tears. In yin, are we “finding the edge, that is in the stretch zone between 2-5%? or is it the plastic zone? and how do we know which is which? (How would you describe what the difference is in the way they each feel? )

    Does static-passive stretching (what I understand we are doing in yin) improve the elasticity of the tissues? Does it improve hydration of the tissues? Does it change the resting length of the tissue after repetition over many months? And if yes, when do we want to lengthen the tissue (tendon?)? When to avoid lengthening? (hyper-mobile people). If so, do you have some references for this that I could look at?

    Finally, how can we best ensure our students stay within “beneficial stress, in order to cultivate resiliency? What are the signs of potential over stress or damage to the tissues (short term and long term)
    Thank you, Lucy

Hi Lucy. Thanks for the question: I will give some short answers first, then the longer explanations behind these answers.
  • 1) We do not want to go to the “plastic, zone in Yin Yoga (but we do want to go where creep occurs....creep is not the same as plasticity, as I will explain later.)
    2) How do we know if we are in the plastic zone? Pain is one key feature. Hypermobility is another (since the tissues will not return to their original length.)
    3) Static passive stretching can improve tissue health as I will describe later, and that does include elasticity, if by that you mean range of motion. It does improve overall hydration of the tissues (although during the stress the tissues dehydrate temporarily)
    4) Do we want larger ranges of motion? For some people yes, for others no-but all tissues need to stay healthy, if not necessarily longer.
Okay, now for the background: I know this area can get confusing so let's start with the basics: In Yin Yoga we target the connective tissues (we affect all tissues, actually, but the connective tissues are the “yin-like, tissues compared to the more “yang-like, tissues of the muscles, so our intention is to work these deeper areas.) This does not mean that there are not other benefits to the practice: there are certainly benefits energetically and mentally/emotionally, but let's just stick to the physical benefits for now.

You asked about the tendons specifically, but connective tissues include the fascia, ligaments, cartilage, bones and joint capsules as well. All these tissues need stress to remain healthy. Which kind of stress is best is debatable and frankly I don't think we know which is best for every body and every tissue, but we can show that long-held static stresses (yin yoga) can be beneficial for each of the tissues listed above.

Your statement “non-linear stress-strain curve of tendons [of] only 8%, is an average: it does not apply to all tendons. Our Achilles tendon and nuchal ligaments stretch far more than that. Some tendons and ligaments don't stretch nearly that much. But your real question is - are we taking the tissues into the plastic zone or only remaining in the elastic stretch zone? And, if so, how do we know? What feelings would arise to give us the clue that we are in the plastic zone?

The short answer is - no, we don't take the tissues into the plastic zone, but we do take them to where creep can occur. My article on creep will explain this in more gory detail, (and I encourage you to read it) but we need to elongate the tissues over time to get the creep effect. You can get something similar by warming up the tissues, but in Yin Yoga we use time to create the creep.

There is a difference between plasticity and creep: plasticity implies a permanent elongation of our tissues once they have passed the tissue's elastic limits. Creep on the other hand is a temporary lengthening that persists after the stresses have ceased, but eventually the tissues regain their original length. Creep stresses do not take the tissues beyond their elastic limits so no permanent remodeling of the collagen fibers occurs. If we take our connective tissues past their elastic limit, we rupture some of the connections between collagen fibers, and indeed we may break the fibers themselves. This can be therapeutic: these microfailures allow the tissues to permanently elongate, increasing range of motion. Over time the body creates new links between collagen fibers and replaces the broken fibers. Sometimes existing fascial crosslinks are inappropriate (such as in scar tissue or adhesions) and we need to break them. With creep, on the other hand, we don't break the fibers or their connections.

Stress on the tissue causes water to be redistributed: water is squeezed out of the fascia into the spaces around the tissue. Water contributes to stability and stiffness in our tissues, making the tissues gel-like (like Jell-O). With less water in the tissues, there is less stiffness and less ability to resist stress, so further lengthening occurs-more creep! When the external stress ceases, the water is slowly reabsorbed into the tissue and the tissue rebounds slowly to its original length and stiffness (1). Many researchers believe that the flow of water into and out of our connective tissue makes the tissues healthier. Robert Schleip describes water in fascia storing free radicals, which can interfere with the healing process, but when the fascia creeps, some of this water is squeezed out of the fascia, along with their free radicals. When the tissue rehydrates later, the free radicals are left behind in the interstitial fluid where they can be more easily neutralized, thus our tissues become healthier (2).

In a Yin Yoga class, the room is not hot, the body is not pre-heated by any exercise or movements, and the postures are entered slowly. But the poses are held for many minutes at a time, allowing creep time to flow to its maximum. One study found that “a time range of 240 seconds is sufficient to have an almost complete development of viscous phenomena. The stress-relaxation curves show that 90% of stress relaxation takes place in the first minute after the application of the strain., (3) In other words, time can do the job just as well as heat. Holding a posture for 4 minutes or longer takes the tissues to their maximum creep, but most of the creep happens in the first minute or two.

Let me point you to a second article I wrote called In Defence of Yin Yoga. There I talk about the difference between stress and stretch:
  • “When a teacher criticizes yin yoga, they are often attacking a straw man. A straw man is a logical fallacy, which presents a proposition that is not the reality and then that proposition is critiqued, not the reality. Take for example the statement; "Yin yoga stretches the connective tissues and that is a very bad thing to do". The fear of "stretching connective tissues" is a straw man: yin yoga does not intend to stretch connective tissues, or ligaments, or joint capsules. If this were the intent, I would agree with the criticism. Yin yoga intends to stress connective tissues, and that does include joint capsules, fascia, ligaments, tendons and even the muscles. Stress is not stretch!

    Let's define a few terms to make this clear: Stress is the force we apply to our tissues and stretch is the resulting elongation, if any, that results from the force. (Technically we could also call stretch strain, although here too some confusion can arise as "strain" could also be used as a verb to indicate stress.) Lots of tissues can stretch: our muscles, tendons, fascia, ligaments, and joint capsules can all elongate--some only a little, others a lot. But for many yoga students, the intention is not to stretch but to strengthen: they need more stability in their joints, not less. To build this stability they still need to stress the tissues, but not to the point of stretching. Stress is not the same as stretch. (It may be more appropriate for yoga teachers, especially yin yoga teachers, to use the verb "stress" when they habitually use the term "stretch.")

    Every tissue in our body needs exercise to remain or regain health. In our yang forms of exercise, we engage our muscles to reduce the dynamic, potentially destabilizing stress on the joints. But, if we are not stressing the joints in our active yoga practice, when can we safely stress these tissues? During yin yoga! During the long held, static stress on our connective tissue, biochemical changes occur at a cellular level: the fibroblasts, chondrocytes and osteoblasts that rebuild our fascia, ligaments, cartilage and bones respond to the mechanical strains that they experience. The fear expressed by those criticizing yin yoga arises due to this misunderstanding: we are not trying to stretch connective tissues. We are trying to stress them.,

You asked about hypermobile students: should they do Yin Yoga? I refer you to another article I wrote on that very topic.

Finally, back to your question about how would we know if we are too far? Pain is one sure signal. If it hurts, tissues are being destroyed. Pain is a broad topic, as you know, and is very subjective so this is a generalized statement, one worthy of a whole other discussion (see my section on pain in my book Your Body, Your Yoga.) But, students can also learn to feel the edge of the pose and by knowing where the edges are, avoid going to far. How to play the edge, let me refer you to one last article.

I hope this helps.
Cheers,
Bernie

1) See Fascia-Clinical applications for health and human performance by Mark Lindsay, pages 54-55: 2008, Delmar.
2) See Robert Schleip, “Lumbar Fasciae: A Frequent Generator of Back Pain. Latest Research Findings and Clinical Implication,, paper presented at the Europäisches Symposium der traditionellen Osteopathie, February 7-10, 2013.
3) See Functional Atlas of the Human Fascial System, by Carla Stecco page 85: 2015 Churchill Livingstone
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