Match the following exercise to the muscle it primarily targets: Single Leg Extension.

The Single Leg Extension primarily targets the hip flexors. This exercise involves extending one leg while keeping the other leg stable, which engages the hip flexors significantly, as they are responsible for raising the thigh towards the torso or bending the hip. When performing the Single Leg Extension, the action primarily focuses on activating and strengthening the iliopsoas and rectus femoris muscles, which are key components of the hip flexor group.

Understanding the roles of the other muscle groups listed can provide further insight into why they are not the primary focus of this exercise. While the glutes are crucial for hip extension and stabilization in many movements, they are not the primary target when performing a Single Leg Extension. The internal obliques are involved in torso rotation and lateral flexion and are not heavily engaged in this specific movement. The erector spinae, which runs along the spine and helps maintain an upright posture, is also not the main focus of this exercise. Thus, the correct identification of the hip flexors as the primary target helps clarify the intent behind the Single Leg Extension.