Which muscles act as the antagonists to knee extension?

• A. Quadriceps femoris
• B. Adductors
• C. Gastrocnemius
• D. Hamstrings and gastrocnemius

Answer: (D)

Knee extension is produced by the quadriceps, so the muscles that oppose that motion are knee flexors. The hamstrings are the main knee flexors, pulling the shin back toward the thigh to bend the knee. The gastrocnemius also crosses the knee joint, so it can help flex the knee in addition to its role at the ankle; this makes it an antagonist to knee extension as well.

The adductors aren’t primary knee flexors and don’t act as significant antagonists to knee extension, and the quadriceps themselves cannot oppose their own action. So the muscles that best oppose knee extension are the hamstrings and the gastrocnemius.