LIMITATIONS IN YOGA
Let's take a look at the main two.
It's quite embarrassing as a yoga instructor not to be able to do the tree pose (vrikshasana) as it is intended, mainly because it is one of the less demanding of the balancing poses, relatively easy and satisfying even for the complete beginner. My problem with it is physical. In theory one should be able to pull ones (bent) knee back, so that the said knee is on the same line as your other leg (imagine being placed and squashed between two pieces of glass - you should be kind of "flat"). My rather disobedient knee will only go back at the expense of my hip bones which unsatisfyingly move around with the offending limb.
There may be different reasons for this; I might be having an "off day", it might be due to tensile restriction or, as Paul Grilley* calls it "compression". "Tensile" means due to muscle (contracted), and "compression" due to the limitations that the architecture of your bones (generally) causes.
Muscle (and ligaments/tendons)
Sometimes a muscle may be contracted: think of a runner who comes in to do her first class of yoga, she may find all the poses which require the ham-strings to stretch, to be particularly demanding. Running tends to cause your leg muscles to shorten or contract. I know this is a horrific generalization, so please take it with a pinch of salt, but guys tend to have more muscle "bulk" and less muscle "length" (I'm thinking legs here) hence for them too the head-to-knee pose for them (janu-shirsasana) may be challenging. The restriction is due to the muscle not being lengthened enough to be able to get comfortably into the position. The good news is when it comes to tensile limitation, there's a lot you can do about it. Yoga for example. Anything that elongates and stretches the muscle will allow for "improvement" (I use the term loosely - personally I give far more clout to what you do on the "inside" during yoga rather that what you manage to achieve physically and aesthetically on the outside).
head-to-knee pose (janu-shirsasana)
Let's get back to my personal physical blot on the landscape. Seeing as I've been doing yoga for nearly ten years (on average four classes a week before teaching) I think my muscles are pretty much pushed to their limit as far as stretch and length is concerned. My problem may be the opposite, due to muscle over-streching ones joints become loose (muscle, ligaments all help to keep your joints well "strapped" in and together, like a kind of muscly support belt. So if this "belt" gets lax, so do the joints and this is not a particularly enviable situation.). So I think I can safely eliminate the "tensile" limitation as my problem in the tree position.
The tree position seen from the front
Then there's "compression". This means that there is contact of some kind that restricts movement in some way. For example two bones knocking up against each other (or muscles being uncomfortably squeezed). I think this is far more likely in my case. What may be the "problem" is either my pelvic bowl: the higher crests and sockets* are pointing slightly inward/forward, rather than being more "open", hence when I bring my knee around the upper neck of my femur bumps up against the offending socket making further movement impossible (without a chainsaw). Or it may be that the socket itself is on the small side and/or the head of the femour on the big side, meaning that there's not much space in there for me to be able to avoid this compression of bone against bone as my knee comes out and back. (this makes perfect sence to me, as I can picture it in my mind, but I wonder of it's understandable to the outsider who's just reading?! Please look at photo's for help!). So if I insist and move my leg back the whole pelvic bowl moves back with it. Does this make the position any less enjoyable, or valid? NO, it does not. If we all had exactly the same bone structure all you would need in yoga is time and patience before being able to do an asana in exactly the same way as your instructor, or the girl next to you on the yoga mat. We all have different body shapes, different bone structure so of course Janu-sirshasana (head to knee pose) for Bob may be completely different to and for Sue. It's interesting to try to understand that if what stops you in a position is tensile (so you can do something about it) or compression (to be accepted with humility, AND enjoyed anyway!).
I will go into the other yoga limitations in a future post.
*For more information on this subject you might want to try out what I consider to be the "yoga anatomy bible" called "Anatomy of Hatha Yoga" by H.David Coulter, or the DVD "Anatomy for yoga" with Paul Grilley.