Answer
Hamstring muscles
These are three muscles in the posterior compartment-- back of the thigh. They are
biceps femoris, semitendinosus and semimembranosus.
Actions: Flex the knee; also extend the knee during and walking.
The biceps femoris flexes the knee , extends the hip, and elevates the trunk from a stooping position: it also laterally rotates the tibia on the fibula when the knee is fixed; in addition, it laterally rotates the femur when he knee is extended, and counteracts forward bending at the hip.
The origin of the biceps: for the long head, the ischial tuberosity; for the short head, the linea aspera, and the lateral supracondylar line of the femur.
The biceps inserts on the head of the fibula
Innervation to this muscle is supplied by the tibial nerve and the common fibular nerve.
The second hamstring muscle is the semitendinosus; It has the following actions: it flexes the knee; medially rotates the the fibula (when the knee is flexed); medially rotates the femur (when the knee is extended), and counteracts forward bedding at the hips
The origin of the semitendinosus is on the ischial tuberosity, and it inserts on the medial surface of the upper tibia. The tibial nerve innervates this muscle.
The semimembranosus is the third of the hamstring muscles
Actions: The actions of this muscle are the same as for the semitendinosus: flexion of the knee, medial rotation of the fibula; medial rotation of the femur, and counteraction of forward bending at the hips.
The semimembranosus originates on the ischial tuberosity. It inserts on on the medial condyle and adjacent tibial margin, on the intercondylar line, , on the lateral condyle of the femur, and on the popliteal ligament.
Innervation for this muscle is supplied by the tibial nerve.
Work Step by Step
The popliteus muscle also acts on the knee, the tibia, and the femur. However, this is not considered one of the hamstring muscles
