Hamstring

The hamstrings are a group of three muscles located on the posterior thigh.

These muscles sit between the hip and the knee joint. They are essential for human movement and stability. The three specific muscles are the semitendinosus, the semimembranosus, and the biceps femoris. They are known as biarticular muscles. This term means they cross two different joints. Because they span both the hip and the knee, they can influence movement in both areas.

To be classified as a "true" hamstring, a muscle must meet four specific criteria. First, the muscle must originate from the ischial tuberosity, which is a part of the hip bone. Second, it must insert over the knee joint on either the tibia or the fibula. Third, the muscle must be innervated by the tibial branch of the sciatic nerve. Finally, the muscle must participate in both knee flexion and hip extension. The adductor magnus is sometimes included in this group. This is because a part of its tendon is morphologically similar to the tibial collateral ligament of the knee. This ligament is attached to the medial epicondyle, just two millimeters from the adductor tubercle.

Each of these muscles has a unique structure and specific job. The semitendinosus and semimembranosus both originate at the ischial tuberosity. They insert on the medial side of the knee. These two muscles help flex the knee and extend the hip. They also help rotate the lower leg medially, which means turning it inward. The biceps femoris is slightly different. It has two parts called the long head and the short head. The long head originates at the ischial tuberosity and inserts on the head of the fibula. The short head originates at the femur and also inserts on the fibula.

While both heads help flex the knee, the long head also helps extend the hip. The biceps femoris also helps rotate the lower leg laterally, or outward.

The history of the word "hamstring" is quite interesting. The term "ham" comes from Old English words like "ham" or "hom." These words originally meant a hollow or a bend in the knee. They also come from a Germanic base meaning "crooked." Around the 15th century, the word began to refer to the leg of an animal. Today, we use it to describe these specific anatomical structures in humans.

Because these muscles are so active, they are often subject to injury. This is especially true for athletes and professional dancers.

In some sports, hamstring injuries account for 19% of all sports-related injuries. On average, these injuries cause an athlete to lose 24 days of competition. The incidence rate is about two injuries per 1000 hours of performance. A common cause is excessive stretching. This happens when there is extensive hip flexion while the knee is extended. During sprinting, an injury might occur during an eccentric contraction. This is a type of contraction that happens late in the leg swing phase.

When a person is injured, doctors use medical imaging to see the damage.

They often use ultrasound or an MRI, which is a magnetic resonance imaging scan. These tools help doctors determine the grade of a muscle strain. They can also see if a muscle is completely torn. Imaging can show the level of retraction, which is how much the muscle has pulled back. The biceps femoris is the most commonly injured hamstring muscle. The semitendinosus is injured next, while semimembranosus injuries are considered rare.

Interestingly, the hamstrings can also be used to help heal other injuries. In a surgical procedure called ACL reconstruction, surgeons can use a piece of the semitendinosus tendon. The ACL, or anterior cruciate ligament, is one of the four major ligaments in the knee. It works alongside the posterior cruciate ligament, the medial collateral ligament, and the lateral collateral ligament. By using the hamstring tendon to replace a damaged ACL, surgeons can help stabilize the knee joint again.