For those who want a serious workout, Ashtanga may be the perfect yoga. Developed by K. Pattabhi Jois, Ashtanga is physically demanding. Participants move through a series of flows, jumping from one posture to another to build strength, flexibility and stamina. It's not for beginners or anyone who's been taking a leisurely approach to fitness. The so-called Power Yoga is based on Ashtanga.