Which of the following is an action of the external abdominal oblique muscle?

• A. Trunk extension and ipsilateral rotation
• B. Plantarflexion of the ankle and flexion of the knee
• C. Trunk flexion with contralateral rotation (and compression of abdominal contents)
• D. Elevation of the scapula and upward rotation of the scapula

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the anatomy and function of the external abdominal oblique muscle. This muscle is located on the lateral and anterior parts of the abdomen and plays a role in movements of the trunk and stabilization of the abdominal wall.
2. Step 2: Recall the primary actions of the external abdominal oblique muscle. It is involved in trunk flexion (bending forward), contralateral rotation (rotating the trunk to the opposite side), and compression of the abdominal contents to support intra-abdominal pressure.
3. Step 3: Analyze each option given in the problem: (a) Trunk extension and ipsilateral rotation - this is generally not an action of the external oblique; (b) Plantarflexion of the ankle and flexion of the knee - these are actions related to lower limb muscles, not the external oblique; (c) Trunk flexion with contralateral rotation and compression of abdominal contents - this matches the known actions of the external oblique; (d) Elevation of the scapula and upward rotation of the scapula - these are actions of muscles like the trapezius, not the external oblique.
4. Step 4: Conclude that the correct action of the external abdominal oblique muscle is trunk flexion with contralateral rotation and compression of abdominal contents, based on the anatomical function and the options provided.
5. Step 5: Remember that understanding muscle actions involves linking muscle location, fiber direction, and attachment points to the resulting movements they produce.