Low back pain is soreness or stiffness in the lumbosacral section of the back (i.e. between the bottom of the ribs and the tops of the legs where the spine curves inwards towards the abdomen). The five vertebrae that comprise the lumbar spine (L1 to L5) are the largest unfused vertebrae in the spinal column. This is necessary as they bear the weight of the torso, and with the lowest two segments (L4- L5 and L5-S1, also known as the lumbosacral joint) under the most pressure, they are understandably the most likely to suffer from injury and deterioration.

In the vast majority of cases, no cause is identified, although it may be attributed to a musculoskeletal strain or minor trauma such as a fall. The discomfort of non-specific back pain usually varies according to posture and time, and worsens upon movement.