Note
It is important to learn Ashtanga Yoga by the traditional method, according to which the next posture is added on only when the student has gained proficiency in the previous one. In this way excessive exertion, fatigue, and unwanted side effects are avoided. Proficiency in a posture can be assessed only by a qualified teacher.
The importance of learning the method from a qualified teacher cannot be stressed enough. It is not possible to learn yoga from a book or video, because these media cannot provide feedback when the student engages in a posture poorly. If this should be the case, little or no benefit would be gained from the practice; in fact damage could be done.