Which muscle is NOT typically considered part of the posterior abdominal wall muscles?

Which muscle is NOT typically considered part of the posterior abdominal wall muscles?

• A. Psoas major
• B. Rectus abdominis
• C. Iliacus
• D. Quadratus lumborum

Answer: (B)

The muscles forming the posterior abdominal wall are the ones that lie behind the viscera and help stabilize the lumbar region and move the hip and spine. Psoas major and iliacus together form a strong iliopsoas that runs along the lumbar region and into the thigh, while quadratus lumborum sits laterally by the iliac crest to brace the lower back. In contrast, the rectus abdominis runs along the front of the abdomen, inside the rectus sheath, and primarily acts to flex the trunk and compress the abdominal contents. Because of its location and function, rectus abdominis is considered part of the anterior abdominal wall rather than the posterior abdominal wall.

The muscles forming the posterior abdominal wall are the ones that lie behind the viscera and help stabilize the lumbar region and move the hip and spine. Psoas major and iliacus together form a strong iliopsoas that runs along the lumbar region and into the thigh, while quadratus lumborum sits laterally by the iliac crest to brace the lower back. In contrast, the rectus abdominis runs along the front of the abdomen, inside the rectus sheath, and primarily acts to flex the trunk and compress the abdominal contents. Because of its location and function, rectus abdominis is considered part of the anterior abdominal wall rather than the posterior abdominal wall.