pain in the lower (lumbar) portion of the back. Lumbago is considered by health professionals to be an antiquated term that designates nothing more than lower back pain caused by any of a number of underlying conditions. The pain may be mild or severe, acute or chronic, confined to the lower back or radiating into the buttocks and upper thighs. It may be caused by a weak or strained back muscle, torn ligaments, a herniated disk, compression of the sciatic nerve ( sciatica), degenerative disease of the vertebrae ( spondylosis), curvature of the spine ( scoliosis), or loss of bone mass ( osteoporosis). Mild lower back pain caused by overexertion can be treated with bed rest, application of heat, massage, anti-inflammatory medication, and strength-building exercise. More severe lower back pain is treated by addressing the underlying condition.