Yin yoga: not just about the fascia?

I am ashamed. As a trained scientist, I should know to question, research and challenge things that I am told, especially before repeating them. So imagine my embarrassment when my 300hrs anatomy teacher challenged me on whether you can work on the fascia separately from the muscle tissue. “But”, I uttered, “what about yin yoga?” Every week I go to class and say that in yin yoga we work on the fascia, the connective tissue that surrounds the muscle. Is that not true?

So, instead of doing the homework we were actually asked to do, I decided I had to figure this out. What is the role of the fascia in yin yoga? I went on trusty PubMed, scrolled through pages of fascia research, read through abstracts and the occasional open access article.

Random things that I discovered:

• This is a rather niche field. You don’t get studies published in high-profile journals, so it’s harder to discern the good studies from the shitty ones. Which makes for an interesting challenge.
• The studies are small! Most seem to have around 14 – 20 participants, which is hardly enough to draw broad conclusions.
• Tied to the above – the samples are skewed! Most of the studies I looked through have recruited young (early 20s) men, presumably students at the university where the study was carried out. I’ve written about the male bias in clinical trials before, interesting to see that the same applies elsewhere. This is important, as hormonal changes in women are known to influence the ability to stretch.

But back to the original question: is yin yoga all about the fascia?

The (bad) answer is, it’s complicated. There is not a single study that at least I could find about yin yoga specifically, so everything I found I had to extrapolate from studies on stretching more broadly.

From an anatomical perspective, it is called myofascia for a reason. Each muscle fibre is bundled together with other fibres in a larger unit called a fascicle, which is surrounded by connective tissue. This means that there is a lot of interconnectedness between the muscle and the fascia; it seems highly unlikely that you can actually work on one without working on the other.

However, the fascia may be a barrier to stretching and therefore stop us from reaching our max range of motion. Likewise (and probably more exciting) is the idea that the nervous system (ie our brain) may also limit how deeply we stretch; think about all the times you’ve been in pigeon and noticed yourself tensing to avoid going deeper. For reference (because I like references!), a couple of studies that propose a link between the nervous system and. flexibility and range of motion after stretching (1, 2).

So, here is my hypothesis:

In yin yoga, we work with long, passive stretches. We hold poses for 3 – 5 minutes (or more, depending on the teacher), easing into the pose, usually in a nice and relaxing atmosphere that is designed to switch the parasympathetic system on.

We work to stretch the muscle and the fascia (as a bundle most likely), but also, crucially, switch off the panic response that sometimes comes from the intensity of stretching, telling our nervous system that it’s ok, it can relax. As time passes, our tolerance to the sensation increases (duration being key here) and, with the nervous system no longer resisting, we can get deeper into the pose.

What do you think? Does that work with your experience of yin yoga?

One more random parting thought:

Excitingly – the original definition of the fascia was that of connective tissue that attaches and surrounds organs BUT now fascia is considered to include a wide variety of tissues, include fat and liquid fascia like lymph. So, technically, as an immunologist, I am also a fasciologist?