A scientific basis for Yin Yoga

[Bernie]

Here is the link to an article I wrote in June of 215 called A Scientific Basis for Yin Yoga. In the footnotes there are many studies cited, but one I love in particular is

• Stretching of the Back Improves Gait, Mechanical Sensitivity and Connective Tissue Inflammation in a Rodent Model by Sarah M. Corey et al in PLoS ONE | www.plosone.org January 2012 | Volume 7 | Issue 1 | e29831

The reason I love this is because they used Yin Yoga on a rat and found "Mechanical input in the form of static tissue stretch has been shown ... to have anti-inflammatory and anti-fibrotic effects.". The above study looked at in vivo effects in rats of static stresses, and was very yin-like: the stretches were held for 5 ~ 10 minute, twice a day, each day for 12 days in a row. The stretch was a whole-body stretch. The results showed that in healthy rats, this exercise improved mechanical sensitivity to low back pain. Rats with simulated inflammation showed more robust benefits from the exercises in sensitivity to pain, gait and superficial fascia thickness (the rats doing the exercises had thinner fascia than the control group, presumably due to less inflammation.)

This study seems to imply that long held, static stresses may help with non-discogenic low back pain, but we cannot infer from this one study whether the cause of the findings are due to localized effects in the fascia or systemic effects from the whole body stress.

[kiwipt]

I am trying to find any research related to the length of optimal time for holding a yin pose. This study on rats is for 5-10 mins, 2x a day, for 12 consecutive days. Are there any studies showing if 5 minutes is enough?; less time? more time?; dependent on the body type of the individual etc. I did my training at semperviva (Granville) in 2012 - and can't find any science for the length of time held in my notes. There was some mention that unloading and reloading fascia during the 5 minute hold didn't lose the lengthening effect on deep fascia - but I have been unable to find this research. Thanks in advance.

[Bernie]

I assume that you have read my article called A scientific basis for Yn Yoga where I talk about those rats you mention. I am not aware of any research on Yin Yoga directly (if anyone comes across such a study, please let me know!) There is some research that shows cyclical loading and unloading of cartilage helps to rebuild or strengthen the cartilage and I have extrapolate those findings to assume the same thing would happen to other connective tissues (ligaments, joint capsules, fascia.) Here is a report I wrote about the 2012 Fascia Congress:

• Cyclical loading and unloading of the cells is required to positively affect tissues. With each loading of a cell, it responds by releasing calcium and ATP (the molecule that provides energy for our bodies at the cellular level) into the extracellular space. However, the cell soon depletes itself and needs to rest to be able to generate more ATP and calcium. This raises an interesting speculation: should we structure Yin Yoga classes (and even yang classes?) so that we repeat the postures but hold them for less time? It may be that the total time needed to achieve optimal remodeling of the tissue need not be achieved in one continuous hold but can be broken up into several shorter sessions?

Another article (In Defence of Yin Yoga) that I have written has some other statistics you may find interesting:

• Studies by Helen Langevin and her coworkers have shown that sometimes we need to let a stress soak in for 30 minutes before "fibroblasts change shape in response to sustained stretching". [1] While we do not hold a single posture for 30 minutes in yin yoga, we may stress a targeted area for that long, through multiple postures. [2] Thomas Myers ... also says sustained stretches are required to allow muscles to relax so that the fascia starts to stretch and release. Long held static stresses have also been found to be beneficial in pain management and reorganizes the connective tissue (again, see Helen Langevin's work.[3])

Finally, another aspect to consider is the effect of time on creep and the relaxation response. I have written about this in an article called Creep and Counterposes:

• 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.”[4] ... Holding a posture for 4 minutes or longer takes the tissues close to their maximum creep, with most of the creep happening in the first minute or two. (Of course that will vary with different people.)

I hope this helps. If you find any other information in your research, please share it with us!
Bernie

1) "Ongoing studies in my lab are addressing why the fibroblasts change shape in response to sustained stretching. So far we have found that the changes are associated with a large-scale relaxation of the connective tissue. We also saw that the fibroblasts initiated a specific Rho-dependent cytoskeletal reorganization that was required for the tissue to fully relax. Rho is an intracellular signaling molecule known to play a role in cell motility and the remodeling of cell-surface proteins that connect the fibroblast to its surrounding matrix. The molecule's involvement in fibroblast shape change suggested that the cells are able to reduce the tissue tension by adjusting how strongly and where they are gripping the surrounding connective tissue or muscle. In addition, we found that the shape change is also associated with a sustained release of ATP from the fibroblast. Within the cell, ATP acts as fuel, but outside of the membrane, ATP can function as a signaling molecule. Extracellular ATP can be converted to other purines such as adenosine, which can act as a local analgesic, thus providing a possible cellular and physiological mechanism to explain the pain relief experienced by some acupuncture patients." From The Science of Stretch, Helene M. Langevin, May 1, 2013, The Scientist.
2) We may perform in sequence Butterfly, Half-butterfly, Saddle and Caterpillar, which together will stress the fascia along the back of the body for 30 minutes or more.
3) Check the same article for a representative example.
4) Note: this does not mean that there is no more creep after 4 minutes. Creep will continue for a long time (see again the picture in the article of silly putty creeping down the wall day after day.) The stress-relaxation reaching a maximum after 4 minutes means that the tissues won't relax any further, but there is still some internal stress, which over time continues to cause creep. See Functional Atlas of the Human Fascial System, by Carla Stecco page 85: 2015 Churchill Livingstone

[Guest]

Thanks Bernie, a great summary of the fascia / yin info. I was hoping there was some newer "science" or papers out there that would give more power to the yin practice theory. Anecdotally yin works for many of my students - but when I am challenged on the basis of the practice I find it difficult to show a study about the effects of long holds on the fascia. Some research seems to indicate it is more the nervous system that adapts rather than the fascia in longer holds - but then I wonder which receptors are adapting - locally in the fascia? muscle fibers? central nervous system? all of these?. If I find anything from the fascianado's I will share.

[Bernie]

It is useful to remember that “the absence of proof is not proof of absence.” Even if we can’t prove Yin Yoga is healthy does not mean that it is not healthy. What is meant by “proof” anyway? I have written elsewhere about the 4 levels of scientific proof: the worst being anecdote. But I have a lot of anecdotes where people have told me that Yin Yoga has really helped them. One lady said she had very bad back pain for years and after several months of yin yoga the pain was all gone. Now that is an anecdote: i can’t say that the postures in Yin Yoga cured her…maybe it was the breath, maybe it was learning to be more mindful, maybe it was just getting out of her house every week, maybe it was being in a community of fellow students? What we can say is that she is feeling better: that is a fact. Why is a mystery. But, without coming to Yin Yoga classes, she most likely would not be feeling better. The challenge, scientifically, is working out why she feels better. The challenge is not to deny that she feels better.

Your comments about the research showing stretching may involve the nervous system and not lengthening the muscles: these studies are valid and worthy of consideration but please note two things about them: 1) they didn’t study yoga, they studied stretching. (Yoga is more than stretching: there is breath, mindfulness, calmness … all of which can activate the parasympathetic nervous system, which simple stretching does not.) 2) The stretches in these studies are almost always held for short periods, on the order of 20 ~ 30 seconds. Most yoga stretches are held for 5 breaths or more, which can be 50 seconds or longer. Plus in Yin Yoga the postures are much longer than that. Finally, while these studies do have some value, they do not seem to explain the reality that many people do lengthen their muscles via yoga: it is not all about the nervous system. These studies have some value, but they don’t explain the full results of yoga practice. We need to keep looking at why it works, but let’s not doubt THAT it works.

Cheers!

[kiwipt]

I agree that because science does prove yin yoga is healthy it does not mean that it is not healthy - 100%. I posed the same "science" question on the anatomy trains facebook page - and received this answer from Tom M thru the page:

He says: "You would have to read contemporary yoga science books to see if such research has been done. I know nothing about 5-10 min specifically - i was taught yoga back in the 70’s when Iyengar recommended 3 minutes.

But I would pose three factors:

1) Individual variation - There isn’t a number that works for everyone. For some, the physiological changes may be done in a shorter time, for others it might be rewarding and delicious to hold the pose for a half and hour.

2) Myotatic reflex release - When you first stretch a muscle, its own stretch reflex tries to re-contract the muscle back to its original length - the same effect is on display when the doctor hits your knee with a rubber hammer. If you maintain the stretch, the reflex gives up after a time and the muscle lengthens. Again, that time varies with the person, but mostly with the training. After you have been in a pose for a bit, theres an ‘Ah!’ feeling as the body relaxes into the pose. That moment will come sooner for the trained yogi, and will take longer for the neophyte. You do not begin to stretch the deep fascia within the muscle until this relaxation occurs, suggesting that new students should hold the pose longer - say, 3 minutes from the ‘Ah’.

3) Move within poses - The ability of the tissue to plastically / visco-elastically deform will depend on local hydration of the specific tissue - IOW, not how much water you rink but how ‘wet’ is the specific fascia you are challenging to stretch. By not going into your ultimate stretch position, i.e. by only going 75% of your stretch capacity, you may look like the stiffest person in the room in terms of the form of the asana, but you will be able to move within the pose, rather than holding still for the full 10 min. While there may be some value in disciplining yourself to stay still, your body will thank you for the extra hydration gained by moving around within the pose."