What is the primary action of the quadriceps muscle group?

The quadriceps muscle group is primarily responsible for knee extension. This group consists of four individual muscles—rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius—that work together to extend the knee joint, allowing for movements such as standing up, walking, and running. When engaged, the quadriceps contract to pull the lower leg upwards and straighten the knee, thereby facilitating tasks that require leg mobility and stabilization.

In the context of the other options, knee flexion involves the hamstring muscles, which are located at the back of the thigh and work to bend the knee. Hip flexion is primarily performed by muscles such as the iliopsoas and the rectus femoris, while hip extension is mainly the responsibility of muscles like the gluteus maximus and hamstrings. Each of these actions highlights different muscle groups and does not represent the primary function of the quadriceps.