Basic anatomy of biceps femoris
It is a long muscle of the back compartment (posterior) of the thigh. It has a long and short head originating from the ischium and hip bone, respectively. The long head forms the part of the hamstrings muscle group and occupies the posterior section of the thigh. The two muscle heads join together away from the head and unite in an intricate fashion. The short head of the biceps femoris joins the belly of the long head in its deep surface as it descends in the thigh.
Functions of biceps femoris
These muscles provide bending (flexion) at the knee and extension at the hip when they contract. When the thigh is flexed, the hamstring muscles help tilt the pelvis backward. The muscle is important for knee flexion, internal and external rotation and hip extension. Tight hamstrings sometimes are associated with lower back pain. This muscle can be used to administer intramuscular injections. Overuse of the muscle could result in tearing of the muscles and ligaments.