Which muscle forms the anterior abdominal wall and serves as the primary trunk flexor?

• A. Rectus Abdominis
• B. External Oblique
• C. Internal Oblique
• D. Transversus Abdominis

Answer: (A)

The front of the abdomen is formed mainly by the rectus abdominis, a vertical, strap-like muscle that runs along the midline. Its fibers pull the upper and lower parts of the spine toward each other when it contracts, producing trunk flexion. Because it lies directly in the midline and forms the visible “six-pack” in people with low body fat, it is the primary muscle responsible for bending the trunk forward and helping to compress the abdominal contents for actions like forced exhalation and postural stabilization.

The other abdominal muscles are located more laterally or deeper (external oblique on the outside, internal oblique and transversus abdominis deeper within). They assist with flexion, rotation, and stabilization, but the rectus abdominis is the main trunk flexor and defines the anterior abdominal wall.