Which muscle compresses the abdomen and is the deepest layer of the abdominal wall?

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

Answer: (A)

The key idea here is that the deepest layer of the abdominal wall is the transversus abdominis, and its role is to tightly compress the abdominal contents. Its fibers run horizontally, like a natural corset, which helps increase intra-abdominal pressure and stabilizes the trunk and spine during movement and maintained posture. This deep layer sits beneath the internal oblique and external oblique, distinguishing it from the more superficial muscles.

In contrast, the external oblique is the outermost layer with fibers running downward and inward, contributing to movements like trunk rotation and lateral flexion. The internal oblique lies just superficial to the transversus and has oblique fibers that assist in rotation and flexion as well as some compression. The rectus abdominis runs vertically along the front and primarily flexes the trunk, not the core compression role.

So, the muscle that both compresses the abdomen and sits as the deepest layer is the transversus abdominis.