What is the primary action of the interspinales?

What is the primary action of the interspinales?

• A. Extension of the vertical column
• B. Ipsilateral flexion
• C. Contralateral rotation
• D. Lateral flexion of the trunk

Answer: (A)

The interspinales are tiny muscles that run between adjacent spinous processes. When both sides contract together, they pull the spinous processes toward each other, straightening and extending the vertebral column. This makes extension the primary action they contribute to, and their role in stabilizing the spine supports posture. They are not the main drivers of bending to the same side or twisting to the opposite side. Those movements involve other deep back muscles that attach to transverse processes or project from the vertebrae, so the interspinales don’t primarily produce ipsilateral flexion, contralateral rotation, or lateral flexion.

The interspinales are tiny muscles that run between adjacent spinous processes. When both sides contract together, they pull the spinous processes toward each other, straightening and extending the vertebral column. This makes extension the primary action they contribute to, and their role in stabilizing the spine supports posture.

They are not the main drivers of bending to the same side or twisting to the opposite side. Those movements involve other deep back muscles that attach to transverse processes or project from the vertebrae, so the interspinales don’t primarily produce ipsilateral flexion, contralateral rotation, or lateral flexion.