Yoga has being associated with one of the best exercises for back pain. When I told my husband that I had back pain after practicing yoga he was really surprise. As a yoga student I was not aware of the limits of my body and I pushed myself too much.
The pain associated with yoga injuries and lower back pain is often related to posture and muscle tone. There are also genetic and structural reasons for back pain but even those conditions are well served by better posture and balanced muscle tone.
The normal backwards can compress our spines in a debilitating way, no matter how slight the compression. It also can cause more serious problems like herniated disc spine injure. The majority of people like me have tight lower back muscles and weak or imbalanced abdominal muscles.
So be aware of the anatomy of your spine and imbalanced muscles. Practice yoga safely and do not push your body beyond its limits. Take care!