Quadratus Lumborum

Origin

Iliac crest and Iliolumbar fascia.

Insertion

Upper 4 lumbar vertebrae and lower margin of 12th rib.

Joint crossed

Intervertebral joints of lumbar vertebrae.

Joint action

Unilateral concentric contraction: lateral flexion of lumbar spine.

Unilateral isometric contraction: prevents lateral flexion of lumbar spine (e.g. when carrying a heavy suitcase in one hand).

Bilateral eccentric contraction: assists in preventing hyperflexion of lumbar spine.