Which muscle is primarily responsible for hip flexion?

The iliacus muscle is primarily responsible for hip flexion due to its anatomical position and functional capabilities. It originates from the iliac fossa of the pelvis and combines with the psoas major to form the iliopsoas muscle group, which is the strongest flexor of the hip joint. When this muscle contracts, it pulls the femur towards the pelvis, effectively reducing the angle between the thigh and the torso, leading to flexion at the hip.

While the gluteus maximus is primarily involved in hip extension and locomotion, the pectineus assists in hip flexion but is not the primary mover. The sartorius does contribute to hip flexion, though it also plays roles in hip abduction and knee flexion. However, the iliacus is the most significant muscle for purposeful and powerful hip flexion movements in activities such as running, jumping, and climbing.