There's an important distinction between "pain" and "suffering." Pain is a reflex reaction, a signal to withdraw from pain-causing stimulus.
Suffering tends to be thoughts and thought-patterns associated with that pain-causing stimulus.
The ashtanga vinyasa yoga gives us the tools to help us clearly perceive this aspect of suffering. This practice is not designed to relieve us of pain, however — though it's not designed to cause us pain, either, despite what other yoga teachers say. (So quit wrenching your leg into lotus!) The effect of physical pain relief through injury rehabilitation is but a secondary effect of the yoga.
The practice of ashtanga vinyasa gives us several tools to cultivate the practice of clear perception: the union of a breathing technique to movement, the internal focal points, and the cultivation of the discipline of a daily practice.
All of which are designed to allow a specific understanding to arise on a somatic level: Suffering is caused not by specific sensations, but by our thoughts associated with those sensations. This realization is the tip of a deeper understanding that we are not, in fact, the sum total of these or any thoughts. The true cause of all our suffering is our identification with our thoughts.
So I'm sorry to report that ashtanga vinyasa yoga isn't going to create a pain-free or even a suffering-free life. Banish from your mind any fantasies of sitting in lotus and floating blissfully miles above the tidal pull of life's glorious little catastrophes.
I've found that ashtanga vinyasa has given me the tools to see with great precision and clarity exactly when my thinking is causing me suffering. Often this suffering arises during the states of the asanas themselves, or transitioning between them.
Some days, a posture will feel much, much harder than it did the previous day, or when I was younger, or when I was uninjured.
The progression of thoughts usually goes like this: The physical stimulus is registered, whether it be stiffness, discomfort, or perhaps pain. Next, it is cataloged in comparison with a previous experience. Finally, I will go on to link a judgment to that comparison: "This sucks," or "This should be easier," or "This was easier last night," or "Why doesn't this feel like Friday night's class?"
Kaboom! Instant suffering arises when reality and my perceptions of reality inevitably fail to match up.
The more insidious aspect of suffering is created when the asanas are enjoyable or pleasurable. It's much easier to root out the thorn than spit out the honey. It's very easy to bask in the sensory pleasure of the endorphin rush of a full series of ashtanga vinyasa. But even this is merely setting the stage for future suffering, because your next practice, and the next one, and the one after that, will now invariably fall short of this internal mental benchmark.
So what to do? The human mind has evolved to organize and catalog, weigh and measure. The Indian goddess of worldy illusion is named Maya, which is derived from a root meaning "to measure, demarcate."
Maya is not someone to suppress, overcome, silence or eradicate. Attempting to do so only riles her up all the more, and gives the mind more to weigh, measure and catalog.
This is where the return to the fundamentals is critical: vinyasa, bandha, drishti. To paraphrase Tim, we work with the soma to influence the psyche. Practiced correctly and consistently, these techniques are simple and powerful enough to allow to arise observation of the maelstrom of the internal dialogue. When you are observing something, you are not participating in it.
One of the techniques to exercise a hyperactive dog, as employed by Cesar Milan in The Dog Whisperer, is to put a weight vest on the canine and let it run on a treadmill. The different series of ashtanga vinyasa will function as your very own consciousness weight-vest and treadmill. Perform them consistently and correctly to the best of your ability, and the hyperactive puppy of your mind will quiet of its own accord.
It's not that thoughts won't arise, nor is it that you'll stop experiencing emotions — the yoga is not a narcotic, after all — but their immediacy, their seriousness, will gradually come to have less an iron-clad grip.