Which movement of the vertebral column would shorten the fibers of the erector spinae?

Which movement of the vertebral column would shorten the fibers of the erector spinae?

• A. Flexion
• B. Lateral Flexion
• C. Rotation
• D. Extension

Answer: (D)

Muscle fibers shorten during a concentric contraction to produce movement. The erector spinae run along the spine and are the primary extensors of the vertebral column. When you extend the spine (straighten up from a flexed or hunched position), these muscles contract to pull the vertebrae toward one another, causing the fibers to shorten. Flexion would require the opposite action, lengthening them as you bend forward; rotation and lateral flexion involve other muscles or unilateral actions and don’t produce the same overall shortening of the erector spinae fibers. Therefore, extension is the movement that shortens the fibers.

Muscle fibers shorten during a concentric contraction to produce movement. The erector spinae run along the spine and are the primary extensors of the vertebral column. When you extend the spine (straighten up from a flexed or hunched position), these muscles contract to pull the vertebrae toward one another, causing the fibers to shorten. Flexion would require the opposite action, lengthening them as you bend forward; rotation and lateral flexion involve other muscles or unilateral actions and don’t produce the same overall shortening of the erector spinae fibers. Therefore, extension is the movement that shortens the fibers.