THE RANGE OF LATERAL FLEXION OF THE LUMBAR AND THORACIC SPINE BY ANTHONY LETT IMAGE 1
Lumbar Spine
Lateral flexion is side bending in the frontal/ coronal plane.
The quadratus lumborum, oblique abdominals, and erector spinae are considered the primary lateral flexors. Note that the internal and external obliques on the same side work to produce the same motion. For example, when bending to your right side (see image 1 above) the right internal and external oblique would contract to pull you into the stretch position. The left lateral flexors would be stretched. If you were to press back into the partner assisting the stretch, the left lateral flexors would contract isometrically. Depending on the specific positioning of the trunk, the semispinalis, deep posterior spinal extensors, rectus abdominus and Illiopsoas also assist with the movement.