Ashtanga yoga is a system of yoga asana practice developed and popularized by Sri K. Pattabhi Jois in the 1940s. (yogapedia.com)
There are many different styles of yoga asana practice: Some are very physical active, with lots of fluid movement in and out of a large number of poses, some quite challenging. (projectwellnessnow.com)
Prerequisite: one year of study and practice of asana in the Iyengar method. (unitywoods.com)