Since I’ve been obsessing about the dull ache and stiffness in my lower back, I decided to do some research. I went to ExTensionYoga. Sam Dworkis has pulled together an excellent resource and he has published two books that may be of use: ExTension and Recovery Yoga. For that matter, it’s good for anyone taking yoga seriously because you have to listen to your body. Dworkis provides good advice; his Seven Principles That Allow You To Safely Practice and Teach Yoga Regardless of Your Level is worth reading for anyone.