Lower back pain is often caused by a muscle strain. The erector spinae, or large paired muscles in the lower back that help keep your spine erect, can become inflamed and spasm. In more serious cases, the pain may be caused by a degenerative condition, such as arthritis, disc disease, or disc herniation.
A degenerative disc condition can sometimes cause a chain reaction of other events in your spine. When a disc is not in its proper place, or is malformed from disease or some other condition, it can allow additional undue pressure on other healthy structures, such as neighboring discs, nerves, muscles, joints, ligaments, and tendons.
Rest, ice or heat therapy, and over-the-counter anti-inflammatory medicine, such as aspirin, are often the first course of treatment for mild lower back pain. This allows your muscles to return to their normal position and begin to heal.
Because the thoracic spine is the sturdiest part of the spine, it is less prone to injury. That said, upper back pain, while less common than lower back pain, is often caused by irritation of the muscles or a problem with a joint. Other less common causes of upper back pain include herniated or degenerative discs.
However, rest for a sore back should be kept to no more than two weeks. Otherwise, the muscles in the lower back begin to atrophy and can become significantly weak, leaving you open to further undue pain and injury.