Are all the hamstring muscles identical in action?

The hamstring muscles are not identical in action. While they all function to flex the knee, each individual muscle also has a unique role:

1. Biceps Femoris (Long Head): The long head of the biceps femoris originates from the ischial tuberosity and inserts onto the fibular head. Its primary action is to flex the knee and laterally rotate the tibia.

2. Biceps Femoris (Short Head): The short head of the biceps femoris arises from the femur and joins the long head to insert onto the fibular head. Like the long head, it flexes the knee and contributes to lateral tibial rotation.

3. Semitendinosus: The semitendinosus originates from the ischial tuberosity and inserts onto the medial surface of the tibia. Its primary function is knee flexion, and it also assists in inward rotation of the tibia.

4. Semimembranosus: The semimembranosus originates from the ischial tuberosity and inserts onto the posterior aspect of the medial condyle of the tibia. It flexes the knee and medially rotates the tibia.

Additionally, the hamstrings work together to extend the hip. This action is particularly important in activities such as sprinting and jumping, where powerful hip extension is required.