Biceps Femoris (Long Head)Long Head of Biceps Femoris

legsCaput longum musculi bicipitis femoris

The long head of biceps femoris is the outer hamstring, running from the sitting bone to the outside of the knee. It extends the hip and bends the knee, and it is the hamstring most often injured in sprinting.

Biceps Femoris (Long Head) highlighted on an anatomical figure, from behind.
Where it sits, from behind.

The long head arises from the sitting bone by a tendon it shares with the semitendinosus, runs down the back of the thigh on the outer side, and attaches mainly to the head of the fibula — the small bony bump on the outside of the leg just below the knee. It forms the outer of the tendon cords you can feel behind a bent knee.

It crosses both joints, so it extends the hip and flexes the knee. Because it attaches on the outer side, it also turns the lower leg outward when the knee is bent — the opposite of what the two inner hamstrings do.

It is the hamstring most often involved in sprinting-related strains, and the mechanics are reasonably well understood: during the swing phase the muscle is lengthening at the knee while contracting hard, which is a demanding combination and one it experiences at high speed. That is a description of the loading pattern, not advice — anything to do with injury is a question for a qualified professional.

Together with the short head beneath it, it makes up the outer half of the back of the thigh and is the larger of the two.

Training notes

It responds to both hamstring jobs, so both Romanian deadlifts and leg curls load it. Because it crosses the hip, hip extension work reaches it in a way that a seated leg curl does not.

Eccentric work — Nordic curls, slider curls, or simply lowering slowly on any curl — loads it in the lengthening pattern that is otherwise only produced by sprinting.

Its external rotation role means that turning the toes slightly outward on a lying leg curl shifts a little more of the work here, and turning them inward shifts it toward the inner hamstrings. The effect is small but it is real.

It is the largest hamstring and gets the largest share of most hamstring work, which is worth knowing when a program seems to have plenty of hamstring volume and the inner hamstrings are still lagging.

Anatomy

Origin
  • Ischial tuberosity, by a tendon shared with the semitendinosus
Insertion
  • Head of the fibula
  • Lateral condyle of the tibia
Actions
  • Flexes the knee
  • Extends the hip
  • Externally rotates the lower leg when the knee is bent
Innervation
Tibial division of the sciatic nerve (L5–S2)

Exercises

Antagonists

Synergists