QL - Quadratus lumborum
ORIGIN - posterior iliac crest / iliolumbar ligament
INSERTION - 12th rib / transverse processes of L1 - L5
ANATOMICAL ACTIONS - lateral flexor of spine and bilaterally extends spine
The QL however also provides stability in the sagittal and frontal planes, with the deep medial fibres contributing to segmental stability of the lumbar spine!
It fixes the 12th rib during inspiration against the pull of the diaphragm as well and so can be considered a respiratory muscle.