Which muscle group comprises the quadriceps and is responsible for knee extension, commonly trained with squats?

• A. Hamstrings
• B. Gastrocnemius
• C. Quadriceps
• D. Gluteus Maximus

Answer: (C)

Knee extension is driven mainly by the quadriceps, a four-muscle group on the front of the thigh (rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius). In a squat, as you rise from the bottom, the quadriceps contract to straighten the knee and lift your body weight, which is why squats are a primary way to train them. The hamstrings flex the knee and assist with hip movement, not extend the knee; the gastrocnemius (calf) mainly helps with plantarflexion of the ankle (and can assist knee flexion a bit), and the gluteus maximus primarily extends the hip. So the muscle group responsible for knee extension and commonly trained with squats is the quadriceps.