Biceps femoris muscle

The biceps femoris muscle is a muscle in the back of the thigh that acts to extend the hip, and flex and lateral|laterally rotate the knee. It is one of the hamstrings.

As the name biceps implies, the biceps femoris has two heads, similar to the biceps brachii muscle in the arm. The two heads are the reason it has two main actions - the long head is solely responsible for extending the hip, while both act on the knee.

Origin
The biceps femoris originates at the ischium bone in the pelvis and the femur.

The long head of the biceps femoris originates from the ischium bone in the pelvis. It attaches to the posterior surface of the ischial tuberosity.

The short head of the biceps femoris originates from the femur at the lateral supracondylar ridge and the middle third of the linea aspera.

Insertion
The biceps femoris inserts at both the tibia and fibula.

The strongest insertion is on the fibula at the fibular styloid process. Weaker insertions are on the lateral collateral ligament and the lateral tibial condyle.

Innervation
The biceps femoris is innervated by two branches of the sciatic nerve (L5, S1). The long head is innervated by the tibial nerve, a branch of the sciatic nerve, and the short head by the common peroneal nerve, also a branch of the sciatic nerve.