During knee flexion, which muscle is the agonist?

During knee flexion, which muscle is the agonist?

• A. Quadricep
• B. Tibialis anterior
• C. Hamstring
• D. Gastrocnemius

Answer: (C)

During knee flexion, the muscle that actively causes the movement is the hamstrings. These muscles run down the back of the thigh and cross the knee joint, so when they contract they pull the lower leg toward the thigh, bending the knee. The quadriceps, by contrast, extend the knee, so they act as the opposite (antagonist) during this action. The tibialis anterior moves the ankle (dorsiflexion) and doesn’t contribute to bending the knee, while the gastrocnemius mainly plantarflexes the ankle and only has a minor, secondary role in knee flexion.

During knee flexion, the muscle that actively causes the movement is the hamstrings. These muscles run down the back of the thigh and cross the knee joint, so when they contract they pull the lower leg toward the thigh, bending the knee. The quadriceps, by contrast, extend the knee, so they act as the opposite (antagonist) during this action. The tibialis anterior moves the ankle (dorsiflexion) and doesn’t contribute to bending the knee, while the gastrocnemius mainly plantarflexes the ankle and only has a minor, secondary role in knee flexion.