Biceps Femoris Muscle

The fusiform biceps femoris, as its name indicates, has two heads: a long head and a short head. It’s one of the hamstring muscles.

The hamstring muscles are (1) semitendinosus, (2) semimembranosus, and (3) biceps femoris (long head). The hamstring muscles (“hamstrings” for short) share the following common features:

• Proximal attachment to the ischial tuberosity deep to the gluteus maximus.
• Distal attachment to the bones of the leg.
• Thus, they span and act on two joints, producing extension at the hip joint and flexion at the knee joint.
• Innervation by the tibial division of the sciatic nerve.

The long head of the biceps femoris meets all these conditions, but the short head of the biceps, the fourth muscle of the posterior compartment, fails to meet any of them.

See Also: Hamstring Muscles

Biceps Femoris Muscle Anatomy

In the inferior part of the thigh, the long head becomes tendinous and is joined by the short head. The rounded common tendon of these heads attaches to the head of the fibula and can easily be seen and felt as it passes the knee, especially when the knee is flexed against resistance.

The long head of the biceps femoris crosses and provides protection for the sciatic nerve after it descends from the gluteal region into the posterior aspect of the thigh. When the sciatic nerve divides into its terminal branches, the lateral branch (common fibular nerve) continues this relationship, running with the biceps femoris tendon.

The short head of the biceps femoris arises from the lateral lip of the inferior third of the linea aspera and supracondylar ridge of the femur. Whereas the hamstrings have a common nerve supply from the tibial division of the sciatic nerve, the short head of the biceps is innervated by the fibular division (Common peroneal nerve). Because each of the two heads of the biceps femoris has a different nerve supply, a wound in the posterior thigh with nerve injury may paralyze one head and not the other.

When the knee is flexed to 90°, the tendons of the lateral hamstring (biceps), as well as the iliotibial tract, pass to the lateral side of the tibia. In this position, contraction of the biceps and tensor fasciae latae produces about 40° lateral rotation of the tibia at the knee. Rotation of the flexed knee is especially important in snow skiing.

Origin	Long Head: Common tendon with semitendinosus from superior medial quadrant of the posterior portion of the ischial tuberosity Short Head: Lateral lip of linea aspera, lateral supracondylar ridge of femur, lateral intermuscular septum of thigh.
Insertion	Primarily on fibular head; also on lateral collateral ligament and lateral tibial condyle.
Innervation	Long Head: Tibial nerve (L5, S1, S2) Short Head: Common peroneal nerve (L5, S1, S2)
Blood Supply	Perforating branches of profunda femoris artery. Inferior gluteal artery. The superior muscular branches of popliteal artery.
Action	Flexes the knee, Also rotates the tibia laterally; long head also extends the hip joint.

In Hamstring strain injury, the biceps femoris long head is the most affected muscle, involving around 80% of all Hamstring strain injury.

See Also: Hamstring Strain

References & More

1. Clinically Oriented Anatomy – 8th Edition
2. Rodgers CD, Raja A. Anatomy, Bony Pelvis and Lower Limb, Hamstring Muscle. [Updated 2023 Apr 1]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK546688/
3. Llurda-Almuzara L, Labata-Lezaun N, López-de-Celis C, Aiguadé-Aiguadé R, Romaní-Sánchez S, Rodríguez-Sanz J, Fernández-de-Las-Peñas C, Pérez-Bellmunt A. Biceps Femoris Activation during Hamstring Strength Exercises: A Systematic Review. Int J Environ Res Public Health. 2021 Aug 18;18(16):8733. doi: 10.3390/ijerph18168733. PMID: 34444481; PMCID: PMC8393607. Pubmed