Which muscle is part of the hamstring group and is responsible for flexing the leg at the knee?

The semitendinosus is indeed part of the hamstring group and plays a crucial role in flexing the leg at the knee. Located at the back of the thigh, this muscle works in conjunction with the other hamstring muscles, including the semimembranosus and biceps femoris, to perform knee flexion. During activities such as running, jumping, or bending the knee, the semitendinosus contracts, which helps to bring the heel toward the gluteal region.

Additionally, the semitendinosus also contributes to hip extension and medial rotation of the tibia when the knee is flexed. Its attachment points and anatomical position support these functions effectively.

In contrast, the adductor magnus does not play a role in knee flexion; it primarily functions in adduction of the hip and some extension. The other hamstring muscles, while also capable of flexing the knee, do not detract from the specific role of the semitendinosus in this context.