thank you for getting back to me. Unfortunately it is both knees. I think I am locking them but I am unable to do standing series very well. I am unable to kick out on either leg, rt is worse. My yoga teacher thinks it is do to very tight hamstrings. I am unablae to do head to knee without bending my knees. As i have said, it has been well over a yr and half. Any suggestions are vey welcomed. I am now trying to do 3 classes a wk as oppossed to my steady 2