The long head arises from the back part of the tuberosity of the ischium and sacrotuberous ligament, the other, the short head, arises from the lateral lip of the linea aspera. These insert into the lateral condyle of the tibia and lateral side of the fibula.
The biceps femoris performs knee flexion and also rotates the knee outward. Muscle weakness leads to knee hyperextension and causes instability.
The semimembranosus and semitendinosus muscles originate from the tuberosity of the ischium, the semitendinosus inserts into the lateral sides of the head of the fibula, and the semimembranosus into the posterior medial condyle of the tibia.
Both muscles are strong flexors of the knee.
They are strong muscles and have a stabilising effect, protecting the knees from joint injuries. That is why is important to include them when we train with neuromuscular electro stimulation, particularly for sports requiring the knee joint.