Which of the following muscles is not typically classified as a knee flexor?

The vastus lateralis is not typically classified as a knee flexor because it primarily functions as a knee extensor. It is one of the four quadriceps muscles located at the front of the thigh. The primary role of the quadriceps group, which includes the vastus lateralis, is to extend the knee joint during activities such as standing up from a seated position, walking, or running.

In contrast, the semitendinosus, biceps femoris, and semimembranosus are all part of the hamstring muscle group, which is responsible for knee flexion. These muscles work by contracting to bring the heel towards the buttocks, playing a key role in movements such as walking, running, and bending the knee. Therefore, among the options provided, the vastus lateralis stands out as the muscle that does not participate in knee flexion.