Which muscle is primarily responsible for torso rotation?

The primary muscle responsible for torso rotation is the external oblique. This muscle is located on the side and front of the abdomen and plays a crucial role in the rotation of the torso. When the external obliques contract on one side, they facilitate trunk rotation toward the opposite side, allowing for movements such as twisting the torso during activities like swinging a bat or reaching across the body.

While internal obliques, which lie beneath the external obliques, also contribute to rotation, their primary function is to rotate the torso toward the same side. This cooperative action between the internal and external obliques is essential for balanced movement and stabilization during dynamic activities.

The rectus abdominis primarily functions to flex the spine and stabilize the pelvis but does not directly contribute to rotational movements. The transverse abdominis, while important for core stability, primarily acts to compress the abdominal cavity and does not play a significant role in rotation. Thus, the external oblique is identified as the key muscle for torso rotation in this context.