I gradually developed severe back pain over the past several years. Tests showed vertebral narrowing causing impingement on the nerve root going to the left leg. Epidural injections did nothing: surgery was recommended. And then ... I happened to stop doing yoga and pilates. Within six weeks the back pain was gone, and has not returned. In my case, the flexion and extension kept daily pressure on the inflamed nerve root, not allowing it to heal; stopping the yoga/pilates allowed the inflammation to end. Weird.
Very weird, yoga does wonders to eliminate my back pain. If my sacroiliac joint ever hurts I do a half hour of yoga and I'm back to normal.
