Biceps femoris: origin, insertion, action and innervation
The biceps femoris has a long head from the ischial tuberosity and a short head from the linea aspera of the femur, and inserts on the head of the fibula. It flexes the knee and the long head extends the hip.
Quick answer
- Latin name
- Musculus biceps femoris
- Origin
- Long head: ischial tuberosity of the hip bone. Short head: lateral lip of the linea aspera of the femur
- Insertion
- Head of the fibula
- Action
- Flexes the knee and rotates the leg laterally when the knee is bent; the long head also extends the hip
- Innervation
- Long head: tibial division of the sciatic nerve. Short head: common fibular division (L5–S2)
- Blood supply
- Perforating branches of the deep femoral artery
The biceps femoris is the lateral hamstring, on the outer side of the back of the thigh. Like the biceps of the arm, it has two heads.
Where it is
It runs down the back of the thigh on the lateral side, next to the semitendinosus and semimembranosus (the medial hamstrings). Its tendon forms the outer border of the popliteal fossa behind the knee, where you can feel it as a firm cord when you bend the knee.
Origin and insertion
- Long head: the ischial tuberosity of the hip bone (the bone you sit on), with the other hamstrings.
- Short head: the lateral lip of the linea aspera on the back of the femur.
- Insertion: the lateral side of the head of the fibula.
What it does
- Knee flexion: both heads bend the knee.
- Lateral rotation of the leg when the knee is bent.
- Hip extension: only the long head, because it alone crosses the hip.
Innervation and blood supply
Its two heads have different nerves, both from the sciatic nerve (L5–S2): the long head from the tibial division, the short head from the common fibular division. Blood comes from the perforating branches of the deep femoral artery.
How to remember it
- Biceps femoris: two heads, two nerve divisions.
- The short head is the only hamstring part that doesn't start on the ischial tuberosity, so it's not a "true" hamstring.
- Biceps femoris to the fibula: B-F, both lateral.
Frequently asked questions
Is the biceps femoris a hamstring?
Yes, it's the lateral hamstring. The hamstrings are biceps femoris, semitendinosus and semimembranosus.
Where does the biceps femoris insert?
On the head of the fibula.
Which nerve supplies the biceps femoris?
The sciatic nerve: tibial division for the long head, common fibular division for the short head.