Which muscle group is the primary knee extensor?

Which muscle group is the primary knee extensor?

• A. Hamstrings
• B. Sartorius
• C. Quadriceps femoris group
• D. Gastrocnemius

Answer: (C)

The main idea is that knee extension is produced by the quadriceps femoris group. These four muscles run along the front of the thigh and attach to the patella via the quadriceps tendon, then to the tibia via the patellar ligament. When they contract, they pull the knee straight, providing the primary force to extend the leg—think of straightening the knee when standing up or kicking a ball. The other muscles don’t serve as the main knee extensor: the hamstrings bend the knee, pulling the leg backward; the sartorius mainly assists with hip actions and knee flexion; and the gastrocnemius crosses the knee and ankle but functions mainly as a ankle plantarflexor, with only a minor contribution to knee flexion rather than extension. So the quadriceps femoris group is the primary knee extensor.

The main idea is that knee extension is produced by the quadriceps femoris group. These four muscles run along the front of the thigh and attach to the patella via the quadriceps tendon, then to the tibia via the patellar ligament. When they contract, they pull the knee straight, providing the primary force to extend the leg—think of straightening the knee when standing up or kicking a ball.

The other muscles don’t serve as the main knee extensor: the hamstrings bend the knee, pulling the leg backward; the sartorius mainly assists with hip actions and knee flexion; and the gastrocnemius crosses the knee and ankle but functions mainly as a ankle plantarflexor, with only a minor contribution to knee flexion rather than extension. So the quadriceps femoris group is the primary knee extensor.