So people don't be scared to start Ashtanga yoga. It looks hard from the outside, but in reality even the most inflexible person can do it and in no time he will start seeing improvements and will enjoy the class more and more. For each level of people there are different modifications for almost every posture in Ashtanga yoga. So if you think you wont be able to do something don't worry, the teacher will show you a version of the posture that you can do. :)