Which muscle is the primary hip flexor?

• A. Iliopsoas
• B. Gluteus maximus
• C. Rectus femoris
• D. Biceps femoris

Answer: (A)

The main idea is which muscle most directly initiates lifting the thigh toward the torso. The iliopsoas is the strongest hip flexor, made up of the psoas major and iliacus. It crosses the hip joint from the pelvis and lumbar spine to the femur, so it produces powerful hip flexion, especially from a standing or neutral position and when the knee is flexed or extended. This primary role is why it’s considered the main hip flexor.

The other muscles listed don’t serve this primary function. The gluteus maximus mainly extends the hip and helps with outward rotation, not a primary flexor. The rectus femoris can assist with hip flexion since it crosses both the hip and knee, but its main job is knee extension, so it’s not the primary hip flexor. The biceps femoris is a hamstring that primarily extends the hip and flexes the knee, not flexing the hip as the main action.

So, the iliopsoas is the best answer because it is the prime mover for hip flexion.