Chronic back pain is usually caused by a herniated or degenerated spinal disk  In most cases the disk will have been damaged years before chronic pain develops, and in fact an estimated one in five people over the age of 30 has a herniated or degenerated disk that shows no chronic symptoms
If chronic pain later develops in such a case, it is generally brought about by a deterioration of the abdominal and spinal muscles caused by insufficient exercise
Four out of five people over the age of 30 can be sure they will never develop chronic back pain.