just want to iterate some words of caution to everyone who is thinking about going to the local gym for a yoga session, esspecially ashtanga. From personal experience and from other peoples aswell.
This isn't ment to put people off learning yoga
be vey cautious from the start it is very easy to injure yourself. Especially with some of the teaching meathods around particually ashtanga, where the teacher comes along and 'helps' you into a posture :rcard . this is very risky as you can be pushed too far.
the thing with yoga is that it was developed in india where people didn't use chairs, so sat on the floor. Where as in the west, everyone will have probably been sitting most of there waking lives in a chair. This causes the hips in particular to be very stiff. making certain postures very difficult and dangerous, namely padmasana(lotus) and half padmasana.
http://www.yogajournal.com/poses/488_1.cfm
my experience with this one. during the asana(posture) my knee would move and lock the knee in a bent posistion, was painful, but if i thought about moving it i imagined that my knee-cap would burst out and possibly injure the person next to me!!! :crutch with the help of the teacher we managed to straighten the leg again where the joint righted itself. this has happened more than a few times and isn't the nicest feeling.
now it first happened when i was 16 so not because i'm some old fart with old joints. I thought at the time i was pritty flexible as i could to the splits!!!
Initially the teacher thought that it could be due to cartalige tear, but had scans and show nothing wrong with the knee at all!
later i found out the main thing with padmasana is hip flexiblity, goes back to sitting on chairs again! After opening the hips somewhat i am now able to do padmasana.
this is probably the biggest issue with men. For woman it would probably be over streching (pulling) the hamstring.
With regards to extreme pranayama and the texts.
asana becomes before pranayama in the yoga sutras of patanjali. meaning once perfecting asana one can then progress to pranayama.
ok this is a very strict path, but think of it this way you wouldn't (unless stupid or mad) go straight to 100m when beginning freediving as a novice. Nor should you go straight to the advanced pranayamas without starting from the beginning.
now the reason why asana becomes before pranayama is so that once mastering the posture one is able to sit perfectly still comfortably an concentrate solely on pranayama. Though practicing basic pranayama and meditation is worthwhile from the start. like most things you have to sow the seeds to reep the rewards.
the books tom (bluh2o) has already mentioned, specifically BKS Iyengars light on yoga, give you a good step by step aproach of asana and pranayama.
better stop here, said more or less,(ok less) everything from my opinion.
sorry for the long post, but it was disrupting my practice!
also have to heavily agree with point 5.