The long muscle of the back with origin (q.v.) in the sacrum and insertion (q.v.) in the thoracic and lumbar vertebrae. Its primary function is to keep the spine erect. A key muscle to be monitored during electromyographic studies of whole body lifting tasks since its response is characteristic of the total effort being expanded. Operates at a poor mechanical advantage and should not be over-stressed in task design or damage to vertebral column or spinal nerves (q.v.) may result. See ERECTOR SPINAE MUSCLES