Muscle · Lumbar spine

Iliocostalis

Musculus iliocostalis

The outermost of the three long columns of muscle that run either side of the spine and hold you upright. Iliocostalis rises from a thick common tendon on the sacrum and the back of the pelvis and reaches up rib by rib to the neck, so it is the column with the best leverage for bending sideways as well as straightening up. It matters clinically because it is the muscle most people mean when they say their lower back is tight: when the hips and the deep core stop sharing the load, this column ends up holding the trunk up all day, and it hardens.