As usual people run for the one magic bullet to fix all their problems. In this case research was done showing that one particular deep ab muscle, when strengthened, decreased back pain. So everyone ran out and worked on this muscle. That is, they overworked the muscle causing instability. The body is never that simple. Muscles work as levers. When one contracts the opposite side relaxes. Also, muscles attach to different parts of the skeleton and other structures. If one muscle is over-strengthened then some other muscle and structure will be over-weakened. The body always strives for balance structurally and physically.