Biceps Femoris (Short Head)Short Head of Biceps Femoris

legsCaput breve musculi bicipitis femoris

The short head of biceps femoris is the only hamstring that does not cross the hip. It starts on the thigh bone, so it bends the knee and nothing else.

The short head arises from the back of the thigh bone itself, lower down than any other hamstring, and joins the long head's tendon on its way to the outside of the knee. It lies underneath the long head and is not visible or palpable separately.

Not crossing the hip makes it the odd one out in every respect that matters. It cannot extend the hip, its length does not change with hip position, and it works the same way whether you are standing, seated or bent forward.

It has a second distinction that is genuinely unusual: it is supplied by a different division of the sciatic nerve from the other three hamstrings. They receive the tibial division; this one receives the common fibular division. Two heads of the same muscle with two different nerves is rare.

Because of its origin on the femur, it is sometimes argued that the short head is not really a hamstring at all in the functional sense, and is grouped with them by position rather than by behaviour.

Training notes

Knee flexion is the whole of it, so leg curls train it directly and Romanian deadlifts barely do. It is the reason a program relying entirely on hip-hinge work leaves part of the hamstrings behind.

Seated leg curls are as effective for it as lying ones, since hip position does not change its length. For the other three hamstrings, hip position matters a great deal — which is what makes the seated curl a useful comparison rather than a redundant exercise.

It cannot be seen or felt separately, so its development registers as thickness on the outer back of the thigh rather than as any distinct shape.

Anatomy

Origin
  • Lateral lip of the linea aspera and the lateral supracondylar ridge of the femur
Insertion
  • Head of the fibula, joining the tendon of the long head
Actions
  • Flexes the knee
  • Externally rotates the lower leg when the knee is bent
Innervation
Common fibular division of the sciatic nerve (L5–S2)

Exercises

Antagonists

Synergists