quadratus lumborum muscle

Between the anterior and middle layer lies the quadratus lumborum muscle.

It forms an arch over the quadratus lumborum muscle.

In contrary to crunches, sit-ups do involve the quadratus lumborum muscle.

Each passes along the lower border of the twelfth rib behind the kidney and in front of the Quadratus lumborum muscle, and is accompanied by the twelfth thoracic nerve.

The superior lumbar (Grynfeltt-Lesshaft) triangle is formed medially by the quadratus lumborum muscle, laterally by the internal abdominal oblique muscle, and superiorly by the 12th rib.

Grynfeltt-Lesshaft hernia is a herniation of abdominal contents through the back, specifically through the superior lumbar triangle, which is defined by the quadratus lumborum muscle, twelfth rib, and internal oblique muscle.