Which muscle compresses the abdomen, depresses ribs, and flexes or rotates the spine?

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

Answer: (A)

The actions described—compressing the abdomen, helping to depress the ribs, and flexing or rotating the spine—fit the external oblique best. The external oblique has fibers that run diagonally downward toward the midline, so when both sides contract it helps flex the trunk and compress the abdominal contents, aiding in forces like expiration. When it contracts on one side, it causes rotation of the trunk to the opposite side, and it also contributes to lowering the rib cage during expiration. This combination of trunk flexion, contralateral rotation, and abdominal compression aligns with the described movements.

The internal oblique also compresses the abdomen and assists flexion, but it mainly rotates the trunk to the same side, not to the opposite side. The rectus abdominis primarily flexes the spine without depressing the ribs in the same way, and the transversus abdominis mainly compresses the abdomen without producing spinal flexion or rotation.