Which large muscle is primarily responsible for extending the knee?

The quadriceps femoris is the large muscle primarily responsible for extending the knee. This muscle group comprises four muscles—the rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius—which work together to extend the leg at the knee joint.

When the quadriceps contracts, it pulls on the patellar tendon, which is attached to the patella (kneecap) and ultimately affects knee extension. This action is vital for movements such as standing up from a seated position, walking, running, and jumping, as the quadriceps plays a crucial role in stabilizing and mobilizing the knee joint during various activities.

In contrast, the other muscles listed have different primary functions. The biceps femoris is part of the hamstrings group, primarily involved in knee flexion rather than extension. The sartorius contributes to hip and knee movements but has a limited role in extension. The tibialis anterior is responsible for dorsiflexion of the ankle and does not influence knee extension, which further underscores the specific role of the quadriceps in extending the knee joint.