The common criteria of any hamstring muscles are:
- Muscles should originate from ischial tuberosity.
- Muscles should be inserted over the knee joint, in the tibia or in the fibula.
- Muscles will be innervated by the tibial branch of the sciatic nerve.
- Muscle will participate in flexion of the knee joint and extension of the hip joint.
Those muscle which fulfills all of the four criteria are called true hamstrings.
The adductor magnus reaches only up to the adductor tubercle of the femur, but it is included amongst the hamstrings because the tibial collateral ligament of the knee joint morphologically is the degenerated tendon of this muscle. The ligament is attached to medial epicondyle, two millimeters from the adductor tubercle.