UPDATED POST (08/18/2017)
Welcome! If you are reading this blog today, please note that I wrote this post in 2014. Years ago. And at a time when I was looking for answers to one big question: Why?
I scoured the exercise and sport science literature looking for reasons behind many of our yoga-isms. As a yoga educator, I wan’t satisfied with just passing on what my teachers taught me. I wanted to give more information, especially a biomechanics education. As you’ll read below, I got pretty good at supporting our yoga beliefs with research.
Since then, I have read a lot more research. I mean, a lot. And something unexpected happen. I started doubting some of our yoga-isms, including the one that is the topic of this blog. You see, that’s the thing about research – it can easily be distorted by a bias, just as easily as it can distort your bias if you’re open to it. Science isn’t binary – you don’t always get a yes or no answer. Most often, the answer is on a spectrum that can depend on the position of the interpreter.
In early 2017, somehow this original post started making its rounds again on social media. I was uncomfortable with the one-sided position I had back in 2014 and even more uncomfortable with the catastrophic language in the post. In response, I wrote the blog, Question Everything. Please take the time to go back and read it after you finish reading this one.
Below you’ll find this original post in its original form. The only change I made other than adding the updated section above, is the title. The original title, “Why is it so bad to transition from externals to neutrals?” was just too negative and fear mongering. I didn’t want it to appear in search engines that way, particularly if the reader didn’t click through to read the full post.
ORIGINAL POST (06/-7/2014):
[Disclaimer: This post has caused quite a social media frenzy. That’s great and it means people are learning and communicating. However, I have concern that some people are now planning to omit this movement from everyday life. I am merely explaining why this transition is discouraged by so many yoga schools. Based on the nature of most group classes, it is not a bad idea to remove it from your sequencing unless you have an understanding of why you would want include it. If are here, you are clearly interested in anatomy, biomechanics and yoga. Please visit my next post, Welcome to my Biomechanics Blog, to learn a little more about who I am, what this blog is about, and what adaptation means.]
Every time I complete a yoga teacher training, I always tell the newly graduated teachers that will I always be available to answer questions for them in the future. Anatomy and biomechanics are not easy subjects to grasp and a lot of good information gets lost in the excitement of learning to become a yoga teacher. But as these teachers go out into the world, they begin to see things and hear things that they want to learn more about. Then the emails roll in.
Yesterday, I received two amazing questions. I’ve decided to share one of them with you here because it is information anyone who practices or teaches yoga should know. I cover it in every teacher training.
Here is the question:
Hey Jules, I am hoping that you can help me with something. I want to read more about why it is so bad to transition from neutrals to externals and vice versa. I generally teach neutrals and externals in separate chains to be safe. However, I want to know WHY it is bad to transition from one to the other. Where is it bad, I assume on the weight bearing leg? I want to know what the parameters are – Half moon to standing splits (very bad), but Warrior 1-Warrior 2? What is safe and what is not exactly? Where can I read more? I got some information [from Google], but still have questions.
Here are the answers (since that wasn’t really one question):
The portion of your bones that make up your joints are covered with articular cartilage. Cartilage is smoother than bone and therefore makes movement easier by reducing friction. Reducing friction allows surfaces to glide over each other with less resistance. Your massage therapist uses oil to reduce the friction between her hands and your skin so she can glide easily without dragging your skin.
Inside the synovial joint capsules (the hip joint is a synovial joint), you have synovial fluid. Synovial fluid is a slippery type of lubrication that helps movement along. But there is actually a lot more. The properties of some of the components of synovial fluid are mind blowing – like super human. Sometimes it binds to the cartilage to increase friction, sometimes it glides across the cartilage to decrease friction. It basically regulates friction inside the joint – all based on the mechanical loading of the environment.1 Practically science fiction, isn’t it?
(Image via Shutterstock)
When you are moving, cartilage is exposed to shear forces. Shear is a gliding force – like the massage therapist gliding her hands across your back. When you are transitioning from Warrior 1 to Warrior 2, your femoral head (top of the thigh bone) is rotating inside the acetabulum (hip joint socket) and the load applied to the cartilaginous lining is a shear force. The cartilage in combination with the synovial fluid is designed to withstand shear forces. But there is always a limit to how much load any material can take.
Thankfully we have engineers to design buildings that can withstand loads and we have biomechanists to teach us how much load our tissues can withstand.
In addition, cartilage is a compressive tissue. Most of the tissues we talk about on this blog are tensile tissues – tendons and ligaments that respond to stretch. Cartilage responds to compression. Just like tendons and ligaments, cartilage also has a stress-strain curve (a.k.a. load-deformation curve). In regular words: the more you compress the cartilage (by standing one leg) the more if deforms. Compression is good for cartilage – but not too much. If the compression goes beyond the mechanical limit, it will fail.
Combine compression and shearing and you now have two forces acting on the tissue. If the amount of compression and shearing is more than the cartilage can withstand, it will fail. Too much friction and the cartilage will fail.
What does failing cartilage look like? It can look a lot of ways, but most common is degrading or tearing.
Degrading cartilage means it starts to thin, to diminish in volume. Continue to increase friction and eventually the cartilage will completely wear through and expose bone. When the cartilage is missing from joint surfaces, it can no longer interact with the synovial fluid and you are left with a bone on bone joint (and LOTS of friction). We call this osteoarthritis.
The tearing is simpler – sort of. It’s just a tear. But now you have a flap of cartilage hanging out getting in the way of movement. Or maybe it tore off, so you have a gashed area. The most common tear is called an acetabular labral tear (acetabulum = hip socket, labrum = lip or rim). Acetabular labral tears are really common in athletes who frequently….wait for it…externally rotate.2
We externally rotate sometimes in yoga, don’t we? I kid. I kid.
Soooooooo, to finally answer the question(s). When you stand one leg and transition from external to neutral (or neutral to external), the combined compression and sheer could create too much friction. You are kinda (sorta maybe) scraping out your joint capsule and giving yourself arthritis. Or setting yourself up for a labral tear or other degenerative joint issues. No bueno.
Transitioning between Warrior 1 and Warrior 2 is not as bad because you aren’t standing one leg. Your weight is distributed between two legs – less compression, less shear under compression, less friction.
But anytime you are balancing on one leg, thecompression increase. Perhaps try to avoid excessive sheer. If you must transition from Half Moon to Revolved Half Moon (or vice versa), I suggest you put the back leg down first, then rotate your pelvis to set up to do the next pose while you are on both feet. [ Update: Yes, this includes Half Moon to Standing Splits. Thank you all who inquired.]
And to answer the follow up questions I always get:
“But my favorite vinyasa teacher cues that transition all the time! I’ve never really liked the way it feels. What do I do?” If you are concerned that this is a situation for overloading, just put your back foot down and adjust before going into the next pose. I do it all the time. I have not been kicked out of class – yet. Oh and SHARE THIS BLOG with everyone you know who practices or teaches yoga!
“But I do it all the time and my hip joint is fine!” Yeah, that’s the thing about collagen tissue injuries. They don’t really hurt until it’s too late. You can’t really tell if your cartilage is degrading, until it’s degraded. Unfortunately, you will have make a choice for yourself on what amounts of compression and sheer you can withstand. I don’t have the answer for you.
Don’t forget to check out my next post Welcome to my Biomechanics Blog, which is what inspired this meme:
(Image by mememaker.net)
 Greene, G. W., Banquy, X., Lee, D. W., Lowrey, D. D., Yu, J., & Israelachvili, J. N. (2011). Adaptive mechanically controlled lubrication mechanism found in articular joints. Proceedings of the National Academy of Sciences of the United States of America, 108(13), 5255–5259. doi:10.1073/pnas.1101002108
 Lewis, C., & Sahrmann, S. (2006). Acetabular labral tears. Physical Therapy, 86, 110–121. Retrieved from http://ptjournal.apta.org/content/86/1/110.short