What action does the short head of the biceps femoris perform?

What action does the short head of the biceps femoris perform?

• A. Flexes leg at knee
• B. Extends thigh
• C. Flexes and medially rotates leg
• D. Flexes and laterally rotates leg at knee

Answer: (D)

The short head of the biceps femoris crosses only the knee joint, not the hip. It originates on the femur and inserts on the fibular head, so its primary action is at the knee: it flexes the leg. When the knee is flexed, the tendon pulls the leg into external (lateral) rotation. It cannot extend the thigh because it does not cross the hip joint. That combination—kneec flexion plus lateral rotation of the leg when the knee is flexed—fits the short head’s role, making the described action the best answer.

The short head of the biceps femoris crosses only the knee joint, not the hip. It originates on the femur and inserts on the fibular head, so its primary action is at the knee: it flexes the leg. When the knee is flexed, the tendon pulls the leg into external (lateral) rotation. It cannot extend the thigh because it does not cross the hip joint.

That combination—kneec flexion plus lateral rotation of the leg when the knee is flexed—fits the short head’s role, making the described action the best answer.