Which of the following pairs of muscles causes contralateral trunk rotation?

To understand why the left internal oblique and right external oblique work together to produce contralateral trunk rotation, it's important to consider their anatomical positions and how they function.

The internal and external obliques are layers of muscles located on either side of the abdomen. The external oblique muscle fibers run in a downward, forward direction, and they are responsible for aiding in trunk rotation, lateral flexion, and flexion of the vertebral column. The internal oblique muscle fibers, on the other hand, run in an upward, forward direction and also assist in similar functions.

When the left internal oblique contracts, it works to rotate the trunk to the right. This is due to its positioning; since the internal oblique is on the left side, its action will pull the torso in that direction. Concurrently, the right external oblique contracts to assist in this rotation. The right external oblique, being on the opposite side, enables the twisting action towards the left side, thus facilitating contralateral rotation.

This coupling of the left internal oblique and right external oblique results in the trunk's rotation toward the opposite side, which exemplifies contralateral movement. This biomechanical relationship is crucial for activities that involve trunk