Synonyms
Latin: Musculus biceps femoris
Definition
The two-headed thigh muscle got its name from the fact that it has two separate origins at the posterior lower pelvis and the posterior lower thigh. These two “muscle heads” come together in their course and move towards the outer knee. The muscle belongs to the back thigh musculature, which is also called ischio-crucial musculature, because it moves from the area of the hip joint (lat.
ischium) to the lower leg (lat. crus). When the muscle contracts, it guides the lower leg towards the thigh/hip and is thus mainly involved in the flexion of the knee joint. A special feature of this muscle group is the so-called Lombard ́sche paradox. It describes the phenomenon that when the leg is fixed – i.e. when the foot is firmly on the ground – the ischio-crucial muscles do not perform their actual function of flexion, but support an extension in the knee joint.
History
Base: Head of fibula (Caput fibulae) Origin: Long head (Caput longum): Ischium (Tuber ischiadicum ossis ischii) Short head (Caput breve): Roughening of the lower third of the femur (Linea aspera) Innervation: Long head (Caput longum): Tibial nerve (segments L5-S2) Short head (Caput breve): Common fibular nerve (segments L5-S2)
Function
As mentioned, the two-headed thigh muscle belongs to the ischio-crucial musculature on the back of the thigh and is therefore one of the most important flexors in the knee joint. Bending in the knee joint is performed, for example, in the one-legged position when the heel is led to the buttocks. Because the muscle starts at the head of the fibula, just below the outer knee, it is the only muscle in the knee joint that can rotate outwards.
The lower leg rotates outwards in the process. The long head of the muscle can also support this movement due to its origin at the hip joint (ischium). It is able to pull the bent leg backwards and thus stretches in the hip joint. It can also turn the leg outwards and therefore counts as an external rotator in the hip joint. Knee joint: flexion (flexion) and outward rotation (external rotation)Hip joint: extension and outward rotation (external rotation)
