Six established and strenuous pose sequences—i.e., the primary series, second series, third series, and so on—practiced sequentially as progress is made. Ashtangis move rapidly, flowing from one pose to the next with each inhale and exhale. (Each series of poses linked by the breath this way is called a vinyasa.) Originating in Mysore, India, the vigorous practice was devised to focus the minds and energy of teenage schoolboys—thus the countless vinyasas. Sri K. Pattabhi Jois brought the style to the U.S. in 1975. And though it's passed through generations of yogis, ashtanga has both stayed true to its roots and branched off in many directions here in the states. Those "vinyasa" or "flow" classes you take? Yep, they can be traced back to this taxing traditional style.