SO....too much yoga, (depending how it is done!!) may even be bad for you. Shock, horror.
Your muscles, ligaments and tendons work together and keep everything in place. If they are tight joints may have problems in mobility. By improving your flexibility you give more moving space to your bones, you create more length between the two (usually) ends of your muscle making touching your toes more feasible for example. However if you over-do it, if your ligaments, tendons and muscles become too lax you compromise your joints - everything becomes loose which may not be such a good thing. Imagine skiing, if you were to twist your knee uncomfortably all the tissue (if tight) surrounding your knee may save it. If however all the tissue is lax your knee joint is simply going to "go with the flow" possibly causing untold damage.
Your muscles can extend to a maximum of 15 %, and ligaments/tendons accommodate no more than 4% without going into damage mode.
The plight of the yoga instructor (and the over zealous practitioner) is this; due to over stretching the muscles (after years and years of yoga) the ligaments and tendons may start to make up for what the muscle is no longer able to give, resulting in over elongated tendons and ligaments which can sometimes cause pain and instability to joints. The muscles themsleves may go over thier limit too again causing pain.
Should I throw away my yoga mat and take up knitting?
No. There are various ways to get around this problem without forcing me into early retirement or you out of the yoga room.
Your body your muscles will let you know when they are over reaching themselves. Your body feels pain, starts trembling not in order to cause you an unnecessary annoying obstacle to the position you are attempting, but as a signal. A signal, one which must be listen too and acted apon. Once you go into over-stretch you nervous system sends messages to the brain causing nerve impulses to act on the "belly" of your muscle resulting in muscle contraction. Your muscle is not contracting in disrespect, but because it NEEDS to, it must PROTECT. Allow this to happen. It may be the case that rather than attempting to move beyond your physical limitations, you are simply going to fast. Your body needs time to adapt.
2. CHANGE FOCUS/OBJECTIVES
Recently a client told me that she was bent on (excuse the pun - I couldn't resist) "continual physical improvement" ie. she wanted to continually become more flexible. As I have just mentioned there is a very definite limit on just how much one can "improve" within this field. Considering the fact she has been doing yoga for many many years I suggested that perhaps it were time to stop pushing so hard, perhaps to physically stop BEFORE she gets to her maximum and concentrate instead on working on the posture using her breathing more than her muscle. Concentrate on creating a breathing pattern that is soft, slow and steady so that she can go beyond her "inner" limits - finding a comfort zone in a position, reaching a relaxation point whilst your muscles are tense and working is an incredible experience. There are no limits when it comes to inner exploration, curiosity and relaxation whilst holding a position, so move your focus from muscle "improvement" to something a little less tangible yet far more rewarding.
3. AN ISOTONIC ALTERNATIVE
I love what I do and I wish to continue - I have no intention of physically falling apart due to lax muscles and loose joints causing me to join the unemployed. So I look after myself. My personal answer to "over-stretch" is probably controversial, is based on personal experience and results rather than on scientific proof, so feel free to take it with a pinch of salt.
I do weights.
In yoga we use "isometric" activity* (holding still under substantial resistance) which favors the lengthening of muscles, lifting weights on the other hand employs "isotonic" activity (shortening of a muscle under constant load) and encourages a shortening/contracting of the muscle. When I started yoga many years ago I confessed to a friend that I did weights as well. She looked at me as if I were mad and exclaimed "but isn't that pointless? Won't one nullify the other?" Suggesting perhaps that I may as well do nothing rather than doing both. And I have to admit that the possibility that yoga will undermine the work I do with weights and vica versa has haunted me for years. However after about ten years I can safely say that, taking my own current physical state and experience as a yard sick, as far as flexibility is concerned I believe I have met my 15% allowance (and am constantly consciously cautious not to go over that) despite weights and yet I am far stronger than I was ten years ago as my weight lifting ability has constantly improved. Does this mean that my joints are more protected than if I'd just done yoga alone? In all honesty I cannot say, but I like to think so. :-) As an instructor I'm very attentive to how my body feels, and I can say that my joints feel like they are protected if that's anything to go by. They certainly do not feel weak or unstable and I do not suffer from pain.
So - feel free to experiment with isotonic activity too rather than isometric alone.
4) AVOID SKIING like the plague ;-). I confess I do.
There is another extremely valid reason to do weights in a previous post which you will find here; http://lpyoga.blogspot.com/2008/10/strength-getting-down-to-bare-bones.html
*consult H. David Coulter's book "Anatomy of Hatha Yoga" to find out more.