which yoga exercises are not good for a bad back?
Answer
Sat Nam,
Whenever there are back problems, the exercises should be doing slowly, paying attention at how you feel and being careful not to feel pain or force the postures.
The ideal thing to do is to do exercises to strenghten the spine, like the ones in the next link. I would recommend to practice yoga with a teacher and ask all your questions to him/her every day.
http://s3cr3ty0stg2.wpengine.com/yoga_4_spine.html
Blessings