Which of the following muscles does NOT stabilize the core?

The psoas major is primarily known for its role in hip flexion and lumbar spine stabilization during movement, rather than actively stabilizing the core in a static or dynamic manner. The core stabilization system includes muscles that work together to maintain a stable and supported pelvis and spine, and while the psoas major aids in movements involving the lumbar spine and pelvis, it does not primarily function as a core stabilizer.

In contrast, muscles such as the diaphragm, transversus abdominus, and internal oblique are specifically designed to stabilize the core region. The diaphragm plays a crucial role in intra-abdominal pressure regulation, assisting in stability during various movements. The transversus abdominus acts as a natural corset, providing support to the spine and pelvis by engaging during activities that require core stability. The internal oblique, meanwhile, contributes to the rotational stability of the trunk and assists in maintaining a stable core during dynamic movements.

Thus, while all the other options are integral to core stabilization, the psoas major's primary responsibilities lie more in its function as a hip flexor and in limited stabilizing roles, which distinguishes it from the other core-stabilizing muscles listed.