One of a pair of fleshy muscles forming part of the posterior abdominal wall. It has its distal attachments on the iliolumbar ligament, next to the iliac crest, and it has its proximal attachment on the last rib and the transverse processes of the first four lumbar vertebrae. Its primary action is lateral flexion of the spine. It also plays a role in maintaining an upright posture.
Subjects: Sports and Exercise Medicine.