What is the unilateral action of the erector spinae group?

What is the unilateral action of the erector spinae group?

• A. Ipsilateral flexion and rotation
• B. Contralateral rotation
• C. Extension of the vertebral column
• D. Abduction of the shoulder

Answer: (A)

Unilateral contraction of the erector spinae mainly causes lateral bending of the spine toward the same side. Because the muscles run along the length of the spine, pulling on one side pulls the vertebral column laterally, producing ipsilateral flexion. The fibers’ orientation can also contribute to a bit of rotation toward the same side, but the primary effect is lateral flexion rather than rotation. The erector spinae are postural extensors; bilateral contraction extends the spine, not a single-side action. They don’t abduct the shoulder, since their attachments and actions are along the vertebral column, not the shoulder girdle.

Unilateral contraction of the erector spinae mainly causes lateral bending of the spine toward the same side. Because the muscles run along the length of the spine, pulling on one side pulls the vertebral column laterally, producing ipsilateral flexion. The fibers’ orientation can also contribute to a bit of rotation toward the same side, but the primary effect is lateral flexion rather than rotation. The erector spinae are postural extensors; bilateral contraction extends the spine, not a single-side action. They don’t abduct the shoulder, since their attachments and actions are along the vertebral column, not the shoulder girdle.