Which muscle is described as the primary hip flexor?

• A. Iliopsoas
• B. Sartorius
• C. Gluteus Medius
• D. Gluteus Maximus

Answer: (A)

Hip flexion is powered most powerfully by the iliopsoas, a deep muscle group made up of the iliacus and psoas major. When these fibers contract, they pull on the femur to lift the thigh toward the trunk, and their line of pull gives them a strong mechanical advantage at the hip joint. This makes the iliopsoas the chief driver of hip flexion during activities like walking, running, and lifting the knee.

The sartorius can assist in hip flexion, but its primary roles are other actions such as assisting with abdominal and leg movements and spanning multiple joints, so it isn’t the main hip flexor. The gluteus medius stabilizes the pelvis and abducts the thigh, and the gluteus maximus extends and externally rotates the hip, not flexes it. So the iliopsoas stands out as the primary muscle for flexing the hip.