Biceps femoris muscle

Origin and insertion

Biceps femoris is the most lateral hamstring muscle located in the posterior thigh. As the name suggests, this muscle has two heads; long and short. These have different origins but share one common insertion.

The long head of biceps femoris muscle originates from the medial facet (inferomedial impression) of ischial tuberosity, medial to the origin of semimembranosus and superior to the origin of adductor magnus muscle. It is important to highlight that this is a shared tendon with both the semitendinosus muscle and sacrotuberous ligament. The tendons of biceps femoris and semitendinosus run together for a distance before separating into two distinct muscles.

The short head originates quite distally from the long head, arising from the lateral lip of the inferior third of the linea aspera and supracondylar ridge of femur. This origin lies medially to vastus lateralis muscle and laterally to adductor magnus muscle.

Near the muscle’s insertion, the long head of biceps femoris continues as an aponeurosis. The muscle fibers from the short head join the aponeurotic sheet, comprising the round common tendon that inserts to the lateral aspect of the head of the fibula. Just prior to insertion, the tendon splits into two slips, passing on either side of the fibular collateral ligament. A few fibers attach to the ligament, a few others spread to the adjacent tibial condyle. When the knee is flexed, the biceps femoris tendon can be easily palpated in the posterolateral aspect of the knee.

Relations

For its largest part, the biceps femoris runs superficially in the posterolateral thigh, sitting deep only to skin, fat and fascial layers. The exception to this is at its superior aspect, where it is covered by the gluteus maximus muscle. While descending from the pelvis into the posterior thigh region, biceps femoris passes on top of semimembranosus muscle, adductor magnus muscle and the lateral head of gastrocnemius muscle.

Along the way, it is also located superficial to the sciatic nerve, providing protection for it. The sciatic nerve gives its terminal branch (common fibular nerve) near the insertion of the biceps femoris. The nerve travels briefly along the medial border of biceps femoris, adhering to the tendon. This is an important clinical relation when considering injury or performing surgery procedures in this region.

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Innervation

The biceps femoris muscle is supplied by the terminal branches of the sciatic nerve. The long head receives innervation from it’s tibial division, while the short is innervated by the common fibular division. Both the tibial and common fibular divisions have the same root values (spinal nerves L5, S1 and S2).

Blood supply

The majority of the blood supply for biceps femoris comes from branches of the deep femoral artery (perforating arteries and medial circumflex femoral artery). Additional supply comes from the inferior gluteal and superior lateral genicular arteries.

Function

In general, the biceps femoris muscle acts on both the knee and hip joints. Although, due to its attachments, the short head of this muscle acts only on the knee joint while the long head acts on both.

When acting on the hip joint, biceps femoris produces the movement of hip extension. This action is the strongest when the trunk is bent forward and is to be brought in an upright position. The biceps femoris is also sometimes described as assisting with external rotation (when the hip joint is in an extended position). When acting at the knee joint, the most prominent action of the biceps femoris muscle is flexion of the leg. This occurs when the lower limb is in an anatomical position. In contrast, when the knee is semiflexed, biceps femoris acts to produce external rotation of the leg at the knee.

Together with other hamstring muscles, biceps femoris stabilizes pelvis, especially during the forward flexion of the trunk occurs. Therefore it has a major role in the gait cycle. Its most important antagonist is the quadriceps femoris muscle which is nearly three times stronger than the hamstrings.

To expand your knowledge check out our learning materials about the muscles  of the hip and thigh. You can expand your knowledge with the video tutorials and actively test yourself with our integrated quizzes.