Which muscle contributes to trunk rotation in the same direction?

The muscle that contributes to trunk rotation in the same direction is the left internal abdominal oblique. The internal abdominal oblique muscle plays a crucial role in trunk rotation by contracting to rotate the trunk towards the same side as the muscle. When the left internal oblique contracts, it causes the torso to rotate counterclockwise, effectively moving the trunk to the left side.

This action is essential in many functional movements, such as twisting during athletic activities, and is vital for maintaining stability and coordination during dynamic movements. The internal obliques work in concert with other muscles, including the external obliques on the opposite side, to facilitate these rotational movements.

In contrast, the right external abdominal oblique would contribute to rotation to the left (opposite side), while the left external abdominal oblique would rotate the torso to the right (again opposite). The right internal abdominal oblique, similarly, would rotate the trunk to the right. Thus, the left internal abdominal oblique is pivotal for executing a leftward trunk rotation efficiently.