Rectus Femoris actions?

Rectus Femoris actions?

• A. Flexion at knee; extension at hip
• B. Adduction at hip; extension at knee
• C. Extension at knee; flexion at hip
• D. Abduction at hip; knee flexion

Answer: (C)

Rectus femoris crosses both the hip and knee joints, so it can affect two different joints at once. Because it attaches across the hip, contracting this muscle helps flex the thigh at the hip. Because it also crosses the knee, contracting it helps extend the knee. This biarticular setup is why its actions are flexion at the hip and extension at the knee, not hip adduction/abduction or knee flexion. The other options describe movements that rectus femoris does not primarily perform.

Rectus femoris crosses both the hip and knee joints, so it can affect two different joints at once. Because it attaches across the hip, contracting this muscle helps flex the thigh at the hip. Because it also crosses the knee, contracting it helps extend the knee. This biarticular setup is why its actions are flexion at the hip and extension at the knee, not hip adduction/abduction or knee flexion. The other options describe movements that rectus femoris does not primarily perform.