What is the action of the multifidus?

• A. Extends the spine
• B. Flexes the spine
• C. Stabilizes vertebrae; assists in extension and contralateral rotation of the spine
• D. Abducts the ribs

Answer: (C)

The multifidus acts as a spine stabilizer with additional actions of extension and contralateral rotation. Its deep, segmental fibers run from transverse processes to spinous processes across multiple levels, enabling it to hold vertebrae in proper alignment during movement. When both sides contract, it helps extend the spine; when it contracts on one side, it assists in rotating the spine to the opposite side (contralateral rotation). This combination best describes its overall function. Abducting the ribs isn’t a role of the multifidus, and spinal flexion is mainly carried out by other muscles.