In standard anatomical position, what is the primary action of the erector spinae muscle group when contracting bilaterally?

• A. Extension of the vertebral column (spinal extension)
• B. Flexion of the vertebral column (spinal flexion)
• C. Depression and retraction of the scapula
• D. Extension of the knee joint

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the anatomical position and the muscle group involved. The erector spinae is a group of muscles located along the vertebral column, primarily responsible for movements of the spine.
2. Step 2: Identify the meaning of 'contracting bilaterally.' This means both the left and right sides of the erector spinae muscles contract simultaneously.
3. Step 3: Recall the primary actions of the erector spinae muscles. When both sides contract together, they act to extend the vertebral column, which means bending the spine backward.
4. Step 4: Differentiate this action from other options: spinal flexion (bending forward), scapular movements (which involve different muscles), and knee joint extension (which involves leg muscles).
5. Step 5: Conclude that the primary action of the erector spinae contracting bilaterally is extension of the vertebral column (spinal extension).