There are many different versions of yoga, an ancient physical and philosophical discipline that started in India.



But to Bob Whittinghill and a number of others in the Chicago area, there is only one kind of yoga that works on all levels: Iyengar yoga, a rigorous form of the discipline that challenges students and teachers to meet its high standards.



Iyengar yoga, first taught in 1936 by B.K.S. Iyengar in India, focuses on physical and spiritual health by "utilizing precision and attention to the best possible relationship of the parts of the body to one another" in the poses that its practitioners make, said Mary Reilly, certification chairwoman of the Iyengar National Association of the United States.



Whittinghill and others in the Chicago area came to teach Iyengar yoga after going through a years-long certification process, which its supporters say is among the most demanding in yoga. Those standards were demonstrated at the From the Heartland regional Iyengar yoga conference, co-sponsored by Iyengar Yoga Association Midwest and the Iyengar Yoga National Association, at Chicago's Palmer House Hilton hotel. The event was held last month.



Whittinghill, who has been practicing this form of yoga for 15 years, said the poses and the spiritual thoughts behind them have helped his soul as well as his body. Iyengar yoga places a strong emphasis on using and holding inversions, such as headstands, shoulder stands and the inverted leg pose (lying on the back with legs on the wall).



"It's become the underpinning of my life, where the ethereal precepts (analogous to the Ten Commandments) have become the guiding principles by which I live and behave in an ethical manner," he said.



Before entering into the Iyengar yoga instructor training program, one must be a student for at least three years; attend at least three classes a week; and practice daily on one's own. Teachers then assess student's practice level to determine when one is ready to begin the instructor training program.



"Our introductory certification (as an Iyengar yoga teacher) calls for mentoring with a more advanced teacher, and taking time, at least two years, to get certified after one has been a student," Reilly said.



There are 2,013 certified Iyengar yoga instructors around the world, according to the B.K.S. Iyengar website. The U.S. has 384 of them. Only England, with 595 certified Iyengar instructors, has more Iyengar yoga instructors.



The hard work is worthwhile, said Whittinghill and other certified Iyengar yoga instructors in the Chicago area. Whittinghill earned his Intro 1 certificate in 2002; Intro 2 certificate in 2004; and the Junior Intermediate certificate in 2008.



Whittinghill said he strives to teach his students to "fall in love with Iyengar Yoga, for it is a wonderful tool to grow old and be sick with."



While Whittinghill teaches full time, Ann Socha and Natasha Julius teach the form of yoga part time while they raise their children.



Socha, who teaches at Yoga Circle in Chicago, the University Club of Chicago and a weekly private class at the Chicago Board of Trade, started teaching in 2000.



But Socha said that because she had to fulfill many prerequisites, it took her five years to get her teaching certification. She had to practice the two to three hours a day, do her required readings and go on weekend workshop retreats.



Julius, Socha's colleague and friend, called Iyengar yoga a labor of love.



With the encouragement and supervision of her teacher, Patrina Dobish, she began teaching in 2005. She apprenticed in Dobish's class at Yoga Circle for close to a year and supplemented this regular teacher training workshops led by senior Iyengar yoga instructors.



In 2007, Julius passed her first teaching assessment by the Iyengar Yoga National Association of the United States and, in 2009, she completed her Intro II certification.



As part of her training, she studied at the Ramamani Iyengar Memorial Yoga Institute in Pune, India, an experience Julius called "a rare privilege."



Julius teaches about eight classes per week at the University of Chicago Yoga Club, University Club of Chicago, and Yoga Circle, in addition to private sessions.



Julius considers yoga a great way to stretch her mind as well as her body, and she tries to share her enthusiasm for Iyengar yoga with her students.



Socha said she is "very appreciative of all Iyengar has taught me."



"I have studied with brilliant people; not flashy people, but people who command respect," she said. "I like the dedication and intelligence. This has become my community of people."