Which muscle is NOT considered a single joint hip flexor?

• A. Gracilis
• B. Sartorius
• C. Iliopsoas
• D. Quadriceps

Answer: (C)

The iliopsoas is not classified as a single joint hip flexor because it crosses the hip joint and plays a significant role in flexing the hip. Specifically, the iliopsoas consists of two muscles: the psoas major and the iliacus, both of which originate from the lumbar vertebrae and the iliac fossa, respectively, and insert into the lesser trochanter of the femur. This anatomical configuration allows the iliopsoas to perform more complex movements beyond simple hip flexion, as it also assists in lateral rotation and stabilization of the pelvis during movement.

In contrast, the gracilis is a single joint muscle primarily involved in adduction and flexion at the hip joint, the sartorius flexes the hip and simultaneously allows for crossing the legs, and the quadriceps group, particularly the rectus femoris component, also affects flexion but can be considered in the context of knee extension, making them more straightforward single joint actions. Thus, while they may play roles in hip movement, they are more isolated in their actions compared to the dual-function capability of the iliopsoas.