The Hamstrings consist of three muscles the Biceps Femoris muscle, the Semitendinosus muscle, and the Semimembranosus muscle. These muscles combined are primarily responsible for the flexion of the knee joint (bending of the knee) as well as assisting the extension of the thigh (moving the upper leg backwards). In addition to these functions the hamstring muscles work in tandem to rotate the knee, assist in maintaining a standing position with knees slightly bent as well as limiting how far we can bend forward as we try to touch our toes without bending our knees. The hamstring muscles also play a role in our posture by assisting to straighten out the lower curvature of the spine which curves the pelvis forward when sitting.
Bicep Femoris Muscle
The origin attachment point of the Biceps Femoris muscle arises as two heads from the Ischial Tuberosity region of the pelvis as a tendon which is shares with the Semitendinous muscle. Another shorter head arises from the outside edged of the Linea Aspera. The fibers of the short head merge into those of the long head, which then have an insertion attachment point on the head of the fibula.
The Semitendinosus muscle has an origin attachment point from the Ischial Tuberosity region of the pelvis as a tendon shared with the biceps femurs. and has an insertion attachment point on the upper shaft of the tibia.
The Semimembranosus muscle has an origin attachment point from just in front of the Semitendinosus muscle on the Ischial Tuberosity region and has five insertion attachment points the main one on the posterior portion of the medial condyle of the tibia a second insertion point is the fascia which covers the Popliteus muscle and the remainder insert joining the Tibial Collateral ligament of the joint and the fascia of the leg.