| Dear Phoenix: Your question is wrong. Iyengar and Ashtanga Yoga are NOT two types of Yoga. They are two types of style of practice and instruction of ONLY one type of Yoga called Hathayoga (mainly). In Ashatnaga, you do more flows, you need extremely athletic and flexiible background. Otherwise, it is USELESS to do for ordinary student. In Iyengar style beginner to Advanced level students can perform at their level and the poses are more aligned. Thus in Iyengar apprach, you get more therapeutic or health benefits, in Ashtanga you get more aerobic, and fitness. However, you can get some additional benefits related to flow and advanced workout in a shorter period in Ashtanga approach, but that applies only if you are prequalified. To make a proper statement, 80 percent of current Ashtanga students including world famous ones are not even prequalified to do it.
Of course, since Yoga is a divine exercise, you will get some benefit from any approach you take.
There is NO harm in your trying both approaches or any additional approaches. But, whether one shall obstruct the progress of the other, depends on your focussing level and prequalification in any particular approach.. So, you shall experinece it within a period of 2 months of regualr practice with multiple approach.
Finally, there are some yoga exercise students who can excel in both approaches. There are others who excel in one and do NOT in another. And, vice a versa.
And, I can guarantee you with all humility, (and while informing you that I am NOT an Iyengar certified teacher), that if you are practicing Iyengar style Yogasana practice correctly and sufficiently, there is NOTHING additional you will gain from Ashtanga style Yogasana practice in terms of Yogasana benefits. But, that does not mean you should not do other things.
Best Luck |