Which muscle is NOT involved in the lateral motion or rotation of the spine?

The rectus abdominis muscle is primarily responsible for flexing the lumbar spine and plays a significant role in movements like bending forward. It is situated at the front of the abdomen and is not oriented for lateral motion or rotation of the spine.

In contrast, the other muscles listed, such as the levator scapulae, erector spinae, and oblique muscles, have functions that facilitate lateral movements and rotation of the spine. The levator scapulae assists in lifting the scapula and can influence the cervical spine, while the erector spinae group helps extend and laterally flex the vertebral column. The obliques, located on the sides of the abdomen, are specifically designed to aid in trunk rotation and lateral flexion. Therefore, the unique action and positioning of the rectus abdominis makes it the muscle not involved in lateral spinal motion or rotation.