Which muscle is considered the prime mover of knee extension?

• A. Gastrocnemius
• B. Biceps femoris
• C. Quadriceps femoris
• D. Semitendinosus

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the concept of a 'prime mover' in muscle actions. A prime mover, also known as an agonist, is the muscle primarily responsible for producing a specific movement.
2. Step 2: Recall the anatomy of the knee joint and the muscles involved in knee extension. Knee extension is the movement that straightens the leg at the knee joint.
3. Step 3: Identify the muscle group responsible for knee extension. The quadriceps femoris group, located in the anterior thigh, is the primary muscle group responsible for this action. It consists of four muscles: rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius.
4. Step 4: Compare the listed muscles to the quadriceps femoris group. The gastrocnemius and biceps femoris are involved in knee flexion, not extension. The semitendinosus is part of the hamstring group, which also contributes to knee flexion.
5. Step 5: Conclude that the quadriceps femoris is the prime mover for knee extension, as it is anatomically and functionally designed to perform this action.