What is antagonistic to the semimembranosus?

The semimembranosus is primarily antagonized by the quadriceps muscle group, which includes the rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. While the semimembranosus is responsible for knee flexion and hip extension, the quadriceps performs the opposite action by extending the knee. Additionally, muscles that flex the hip, such as the iliopsoas, can also be considered antagonistic in a broader context.