Which of the following muscles is NOT an external rotator of the hip joint?

The Tensor Fasciae Latae (TFL) is not classified as an external rotator of the hip joint. Instead, its primary functions include hip flexion, abduction, and stabilization of the pelvis during walking and other movements. While it can contribute to a degree of internal rotation, its main roles do not align with external rotation activities.

In contrast, the other muscles listed—Piriformis, Gluteus Medius, and Gemellus Superior—are well-established external rotators. The Piriformis is particularly notable as it not only assists with external rotation but also plays a significant role when the hip is flexed. The Gluteus Medius, although primarily an abductor, also aids in external rotation. Gemellus Superior contributes primarily to external rotation as well.

Understanding the specific functions of these muscles is crucial for effectively designing and executing Pilates exercises focused on hip mobility and stability.