Asana "Hatha Ratnavali" provides a list of 84 asanas, describing some of them. In the 20th century, Tirumalai Krishnamacharya taught a new system of asanas, incorporating systems of exercises as well as traditional hatha yoga, to influential Indian yoga teachers including Pattabhi Jois, founder of Ashtanga vinyasa yoga, and B.K.S. Iyengar, founder of Iyengar yoga. Together they described hundreds more asanas, revived the popularity of yoga, and brought it to the Western world. Many more asanas have been devised since Iyengar's 1966 "Light on Yoga" which described some 200 asanas; some 300 were created by Dharma Mittra. Asanas have been claimed
Ashtanga vinyasa yoga classes in similar style, offering posture variations, and teaching Ashtanga in a much less linear style, with a greater emphasis on alignment and breathing. Sharath's "new generation" of young students have adopted Sharath's new rules, and teach in a linear style without variations. According to the Sharath generation, variations are not allowed, and practice must be in a strict Mysore environment under the guidance of a Sharath-approved teacher. How-to videos & workshops, detailed alignment instructions, and strength-building exercises are not part of the method, neither for the practitioner or the teacher. These types of instruction are not approved by Sharath,