Which muscle helps in extending the thigh and medially rotating the leg?

The semimembranosus is a key muscle in the posterior compartment of the thigh, primarily functioning to extend the thigh at the hip joint. It also plays a role in medial rotation of the leg at the knee when the leg is flexed. This dual action is significant as it facilitates movements such as walking or running by enabling the hip to extend while allowing internal rotation to occur at the knee.

The muscle's anatomical position and attachment points are designed for these specific actions, making it a crucial component of both the hamstring group and the overall mechanics of the lower body. Understanding the roles of various muscles in functional movements emphasizes the importance of correct muscle selection during exercise and rehabilitation programs.