Which muscle acts as a synergist with the piriformis during lateral rotation of the hip?

• A. Sartorius
• B. Gluteus Maximus
• C. Tensor Fasciae Latae
• D. Piriformis

Answer: (A)

The idea here is about muscles that help produce the same movement together, a synergy. Lateral (external) rotation of the hip is driven by several muscles, with the piriformis being one of the deep external rotators. A synergist is another muscle that can assist this rotation.

Sartorius fits as a synergist because it crosses the hip in a way that, when the thigh is flexed, it can contribute to external rotation. In that flexed position, sartorius helps rotate the thigh outward alongside the piriformis, making them work together to achieve lateral rotation.

The tensor fasciae latae mainly assists with flexion and medial rotation when the hip is flexed, not external rotation. Gluteus maximus is a strong external rotator, especially in extension, but it’s more of a primary mover in those conditions rather than a typical synergist with piriformis across common positions. Piriformis itself isn’t a synergist with itself.

So, sartorius is the best match as a synergist with the piriformis during hip lateral rotation, particularly when the hip is flexed.