Which abdominal muscle is most important for spinal flexion and posterior pelvic tilt?

• A. External oblique
• B. Rectus abdominis.
• C. Transverse abdominis
• D. Internal oblique

Answer: (B)

Rectus abdominis is the main driver of spinal flexion and posterior pelvic tilt. This vertical strap-like muscle runs from the pubic bone up to the lower ribs and xiphoid process. When it shortens, it pulls the front of the trunk forward, bending the spine toward the pelvis. Simultaneously, its pull on the pelvis helps tilt the pelvis backward, reducing the lumbar curve. That combination is why it’s the primary muscle for both flexing the spine and achieving posterior pelvic tilt.

External and internal obliques can assist with flexion when both sides act together, but they’re also key for lateral flexion and rotation, so they’re not the primary movers for pure spinal flexion. Transverse abdominis, the deepest layer, stabilizes the spine and increases intra-abdominal pressure rather than producing spinal flexion.