The erector spinae muscles are a group of long muscles that originate near the sacrum and extend vertically up the length of the back. The erector spinae muscles lie on each side of the vertebral column and extend alongside the lumbar, thoracic, and cervical sections of the spine.

The erector spinae muscles function to straighten the back and provide for side-to-side rotation. An injury or strain to these muscles may cause back spasms and pain.