The muscles of the vertebral column are covered by more-superficial back muscles, such as the trapezius and latissimus dorsi muscle (Figure 11-3b. The erector spinae, or spinal extensors, include superficial and deep layers. The superficial layer can be divided into spinalis, longissimus, and iliocostalis divisions (Figure 11-11 and Table 11-8). In the inferior lumbar and sacral regions, the boundary between the longissimus and iliocostalis muscles is indistinct. When contracting together, the erector spinae muscles extend the vertebral column. When the muscles on only one side contract, the result is lateral flexion of the vertebral column.

Deep to the spinalis muscles, the muscles of the vertebral column interconnect and stabilize the vertebrae. These muscles include the semispinalis muscles and the multifidus, interspinales, intertransversarii, and rotatores muscles (Figure 11-11a, b). In various combinations, they produce slight extension or rotation of the vertebral column. They are also important in making delicate adjustments in the positions of individual vertebrae, and they stabilize adjacent vertebrae. If injured, these muscles can start a cycle of pain muscle stimulation contraction pain. This cycle can lead to pressure on adjacent spinal nerves, leading to sensory losses as well as limiting mobility. Many of the warm-up and stretching exercises recommended before athletic events are intended to prepare these small but very important muscles for their supporting role.

The muscles of the vertebral column include many dorsal extensors but few ventral flexors. The vertebral column does not need a massive series of flexor muscles, because (1) many of the large trunk muscles flex the vertebral column when they contract, and (2) most of the body weight lies anterior to the vertebral column, so gravity tends to flex the spine. However, a few spinal flexors are associated with the anterior surface of the vertebral column. In the neck, the longus capitis and the longus colli muscles rotate or flex the neck, depending on whether the muscles of one or both sides are contracting (Figure 11-11c). In the lumbar region, the large quadratus lumborum muscles flex the vertebral column and depress the ribs (Figure 11-11a).