What is the function of the semimembranosus muscle?

The semimembranosus muscle plays a crucial role in the movement of the thigh and leg. Its primary functions include extending the thigh at the hip joint and facilitating flexion and medial rotation of the leg at the knee joint. When the semimembranosus contracts, it helps to pull the thigh backward, which is essential for movements such as walking or running.

Additionally, when the knee is bent, the semimembranosus aids in the medial rotation of the leg. This dual function—extension of the thigh and flexion combined with medial rotation of the leg—makes this muscle vital for maintaining stability and mobility in lower body movements.

The other options do not accurately describe the functions of the semimembranosus. For instance, adducting the thigh is not a primary function of this muscle, and plantar flexion pertains to muscles located in the calf rather than the semimembranosus. Thus, the correct choice highlights the essential actions of this muscle in leg movement and stabilization.