|Origin||Long head: Ischial tuberosity|
Short head: Linea aspera and the lateral supracondylar line of the femur
|Insertion||Long & short head: Lateral head of fibula|
|Action||Long & short head: Knee flexion and lateral rotation of leg|
Long head: Hip extension
|Nerve||Long head: Tibial division of sciatic nerve (L5, S1, S2)|
Short head: Common fibular division of sciatic nerve (L5, S1, S2)
|Artery||Deep femoral artery (profunda femoris artery) and its perforating branches|
Location & Overview
The biceps femoris muscle is situated in the posterior compartment of the thigh and is one of the three muscles that form the hamstring muscle group. The other two hamstring muscles are the semimembranosus and semitendinosus muscles. The biceps femoris is unique among the hamstring muscles as it has two heads, a long head and a short head. These two muscle heads work together to contribute to its functions discussed in the actions section below  .
The long head of the biceps femoris muscle is located medially, while the short head is located laterally. The muscle is located superficially in the posterior part of the thigh, with the semimembranosus and semitendinosus muscles positioned medially to it. The biceps femoris muscle runs along the lateral side of the thigh and can be easily palpated on the back of the leg when the knee is flexed. The long head of the biceps femoris muscle crosses both the hip and knee joints, allowing it to participate in movements at both joints. In contrast, the short head only crosses the knee joint, limiting its involvement to actions at just the knee joint  .
Origin & Insertion
The biceps femoris muscle has two separate origins, one for each of its two heads. The long head originates from the hip’s ischial tuberosity. The ischial tuberosity is bony protrusion located on the posterior aspect of the ischium, which is the lower part of the hip bone. This origin point is shared with the other two hamstring muscles (semimembranosus and semitendinosus)  . The short head of the biceps femoris muscle originates from the linea aspera and the lateral supracondylar line of the femur. The linea aspera is a roughened ridge on the posterior shaft of the femur. The lateral supracondylar line extends laterally from the bottom of the linea aspera and it is a ridge found on the lateral, distal and posterior side of the femur  .
The two heads of the biceps femoris muscle continue down the lateral aspect of the thigh where they insert onto the lateral side of the head of the fibula. The tendon of the biceps femoris muscle is divided at its insertion point by the fibular collateral ligament of the knee (also known as the lateral collateral ligament)  .
The biceps femoris muscle contributes to various movements at the hip and knee joints and its two muscular head contribute to different actions. The primary function of both heads of the biceps femoris muscle is to flex the knee joint. Knee flexion involves bending the knee and bringing the lower leg closer to the back of the thigh   .
Along with knee flexion, the long head of the biceps femoris muscle also assists in hip extension. This is because it originates from the ischial tuberosity and crosses the hip joint (the short head does not cross the hip joint). Hip extension happens when the thigh moves backward (posteriorly) in relation to the hip, such as pushing off the ground when walking. The long head’s effectiveness in knee flexion and hip extension varies depending on the position of the joints. It is more effective at knee flexion when the hip is flexed and more effective at hip extension when the knee is extended   .
Furthermore, the biceps femoris muscle is involved in lateral rotation of both the femur and the tibia. The long head contributes to lateral rotation of the femur when the hip is extended, while the short head, which only crosses the knee joint, assists in lateral rotation of the tibia when the knee is slightly bent. Lateral rotation, also called external rotation, refers to the outward rotation of the leg relation to the body’s midline   .
The two heads of the biceps femoris muscle are innervated by separate branches of the sciatic nerve. The sciatic nerve is the longest nerve in the human body and starts from the lumbar and sacral spinal nerves of L4 to S3. The long head of the biceps femoris muscle is innervated by the tibial division of the sciatic nerve (L5, S1, and S2). The short head of the biceps femoris muscle is innervated by the common fibular (peroneal) division of the sciatic nerve (L5, S1, and S2) .
The primary blood supply for the biceps femoris muscle is the deep femoral artery (also known as the profunda femoris artery). This artery branches off from the femoral artery and travels deep within the thigh, providing a blood supply to the hamstring muscle group. The biceps femoris muscle also receives blood from the perforating arteries/branches. The perforating arteries are smaller branches which arise from the deep femoral artery .
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Biceps Femoris Flashcards
|↑1, ↑3, ↑8, ↑10||Moore KL, Agur AMR, Dalley AF. Clinically Oriented Anatomy. 8th ed. Philadelphia: Lippincot Williams & Wilkins; 2017.|
|↑2, ↑4, ↑5, ↑13, ↑16, ↑18||Standring S. (2015). Gray’s Anatomy: The Anatomical Basis of Clinical Practice, 41st Edn. Amsterdam: Elsevier|
|↑6, ↑7, ↑9, ↑12, ↑15, ↑19||Rodgers CD, Raja A. Anatomy, Bony Pelvis and Lower Limb, Hamstring Muscle. [Updated 2021 Aug 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK546688/|
|↑11, ↑14, ↑17, ↑20||Afonso J, Rocha-Rodrigues S, Clemente FM, et al. The Hamstrings: Anatomic and Physiologic Variations and Their Potential Relationships With Injury Risk. Front Physiol. 2021;12:694604. Published 2021 Jul 7. doi:10.3389/fphys.2021.694604|
|↑21||Tomaszewski KA, Henry BM, Vikse J, Pękala P, Roy J, Svensen M, Guay D, Hsieh WC, Loukas M, Walocha JA. Variations in the origin of the deep femoral artery: A meta-analysis. Clin Anat. 2017 Jan;30(1):106-113. doi: 10.1002/ca.22691. Epub 2016 Feb 2. PMID: 26780216.|