In seated hip flexion with the right foot on the left knee, which muscle is the prime mover?

In seated hip flexion with the right foot on the left knee, which muscle is the prime mover?

• A. Iliopsoas
• B. Sartorius
• C. Tensor fasciae latae
• D. Psoas major

Answer: (B)

In this seated cross-legged position, the Sartorius becomes the main driver of hip flexion. The Sartorius runs from the front of the pelvis to the inner side of the knee, crossing the hip joint in a way that, when the knee is flexed (as it is when the foot rests on the opposite knee), its line of pull effectively pulls the thigh upward toward the trunk. This “tailor’s” position specifically favors the Sartorius’ action of flexing the hip while the knee is flexed and the thigh is externally rotated, making it the primary mover here. The iliopsoas (including psoas major) is a very strong hip flexor, but its mechanical advantage for hip flexion is greater when the knee is extended or in neutral. With the knee flexed in this pose, its contribution is not the dominant flexor. The Tensor fasciae latae can help with hip flexion, but its role is secondary to the Sartorius in this particular posture.

In this seated cross-legged position, the Sartorius becomes the main driver of hip flexion. The Sartorius runs from the front of the pelvis to the inner side of the knee, crossing the hip joint in a way that, when the knee is flexed (as it is when the foot rests on the opposite knee), its line of pull effectively pulls the thigh upward toward the trunk. This “tailor’s” position specifically favors the Sartorius’ action of flexing the hip while the knee is flexed and the thigh is externally rotated, making it the primary mover here.

The iliopsoas (including psoas major) is a very strong hip flexor, but its mechanical advantage for hip flexion is greater when the knee is extended or in neutral. With the knee flexed in this pose, its contribution is not the dominant flexor. The Tensor fasciae latae can help with hip flexion, but its role is secondary to the Sartorius in this particular posture.