Pain Answer: Back pain can be caused by spinal irritation and back nerve damage. While the spine is sensitive to posture and body position, it is also suspended and retained in position by a comple series of muscles and ligaments. Standing in a good upright posture places the spine and back nerves in the ideal orientation to cause less pain. By sitting down, the back is often repositioned into an orietation that places additional stress on the offending vertebrae and/or back nerves. By relaxing, the back muscles let go and your posture can drift. The motion of the bones and muscles into a relaxed position can agitate the nerves that were happy in the upright posture.