Back pain can come on suddenly and last less than six weeks (acute), which may be caused by a fall or heavy lifting. Back pain that lasts more than three months (chronic) is less common than acute pain. Back pain often develops without a specific cause that your doctor can identify with a test or imaging study. Conditions commonly linked to back pain include: Muscle or ligament strain. Repeated heavy lifting or a sudden awkward movement may strain back muscles and spinal ligaments. If you're in poor physical condition, constant strain on your back may cause painful muscle spasms.