Which muscle is NOT part of the lateral trunk muscles?

The rectus abdominis is correctly identified as not being part of the lateral trunk muscles. This muscle runs vertically along the front of the abdomen and is primarily responsible for flexing the spine and stabilizing the pelvis. It plays a crucial role in movements such as bending forward and maintaining posture, but it does not contribute significantly to lateral flexion or rotation of the trunk.

In contrast, the quadratus lumborum, internal oblique, and external oblique are all involved in lateral movements. The quadratus lumborum assists in stabilizing the pelvis and spine and aids in lateral flexion of the trunk. The internal and external oblique muscles are both involved in trunk rotation and lateral flexion as well, working together to support a wide range of movements in daily activities and exercise. Understanding the distinction between these muscle groups is important for comprehending core dynamics and their functions in Pilates and other physical activities.