Studies show back pain patients often have muscle wasting on the same side as the symptoms. It's not clear yet which came first, the injury or the weakness. Some say since the muscle changes are seen right after back pain starts that the weakness led to the injury.
Others show an inactive lifestyle is what causes muscle weakness AND injury. If this theory is true then back injury isn't caused by some problem inside the spine. This means back pain and injury can be prevented with exercise.
There are enough studies on both sides of the issue to suggest both cases are true. It's possible that some back problems come about because of inactivity while others occur as a result of some intrinsic problem.