Low back pain can be caused by many reasons, and some of the most common include stiff or pulled muscles, herniated discs in the lower spine, arthritis, pregnancy, and sciatica. Mechanical low back pain means the source of the pain is the result of something not working properly in the spine or supporting structures. Most commonly, this occurs when one or more of the joints in the spine lacks motion. When a joint loses motion, it can lead to dysfunction and cause pain. Joint dysfunction can also cause muscle imbalance and muscle pain surrounding the area.