Hamstring
A hamstring is any one of the three posterior thigh muscles in human anatomy between the hip and the knee: from medial to lateral, the semimembranosus, semitendinosus and biceps femoris.
Etymology
The word "ham" is derived from the Old English “ham” or “hom” meaning the hollow or bend of the knee, from a Germanic base where it meant "crooked". It gained the meaning of the leg of an animal around the 15th century. String refers to tendons, and thus the hamstrings' string-like tendons felt on either side of the back of the knee.Criteria
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.
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 the medial epicondyle, two millimeters from the adductor tubercle.
Structure
The three muscles of the posterior thigh flex the knee, while all but the biceps femoris extend the hip. The three 'true' hamstrings cross both the hip and the knee joint and are therefore involved in knee flexion and hip extension. The short head of the biceps femoris crosses only one joint and is therefore not involved in hip extension. With its divergent origin and innervation, it is sometimes excluded from the 'hamstring' characterization.| Muscle | Origin | Insertion | Nerve |
| semitendinosus | ischial tuberosity | medial surface of tibia | tibial part of sciatic |
| semimembranosus | ischial tuberosity | medial tibial condyle | tibial part of sciatic |
| biceps femoris - long head | ischial tuberosity | lateral side of the head of the fibula | tibial part of sciatic |
| biceps femoris - short head | linea aspera and lateral supracondylar line of femur | lateral side of the head of the fibula | common peroneal |
A portion of the adductor magnus is sometimes considered a part of the hamstrings.
Function
The hamstrings cross and act upon two joints – the hip and the knee – and as such they are termed biarticular muscles. The hamstrings contract when the knee is bent or when the hips are extended, and they lengthen when the knee is extended.Semitendinosus and semimembranosus extend the hip when the trunk is fixed; they also flex the knee and medially rotate the lower leg when the knee is bent.
The long head of the biceps femoris extends the hip, as when beginning to walk; both short and long heads flex the knee and laterally rotate the lower leg when the knee is bent.
The hamstrings play a crucial role in many daily activities such as walking, running, jumping, and controlling some movement in the gluteus. In walking, they are most important as an antagonist to the quadriceps in the deceleration of knee extension.