Hamstring
Three posterior thigh muscles crossing hip and knee.
Here is the rewritten encyclopedia entry:
The hamstrings are a group of three muscles running down the back of the thigh, connecting the hip to the knee. From the inner to the outer side of the leg, these are the semimembranosus, semitendinosus, and biceps femoris. The name comes from Old English: "ham" originally referred to the bend or hollow of the knee, while "string" points to the tendon-like cords you can feel on either side of the back of the knee.
To be considered a true hamstring, a muscle must start at the ischial tuberosity (the sitting bone), attach below the knee joint on the tibia or fibula, be powered by the tibial branch of the sciatic nerve, and help both bend the knee and straighten the hip. The adductor magnus muscle is sometimes grouped with the hamstrings because its tendon has evolved into the tibial collateral ligament of the knee.
All three main hamstrings bend the knee, and all except the short head of the biceps femoris also straighten the hip. The short head of the biceps femoris only crosses the knee, so it doesn't help with hip extension. Because of its different origin and nerve supply, it is occasionally left out of the hamstring group. A portion of the adductor magnus is also sometimes included.
Because they cross two joints, the hamstrings are biarticular. They tighten when you bend your knee or extend your hip, and they lengthen when you straighten your knee. The semitendinosus and semimembranosus extend the hip when your trunk is still, bend the knee, and rotate the lower leg inward when the knee is bent. The long head of the biceps femoris extends the hip (as when starting to walk), while both heads of the biceps femoris bend the knee and rotate the lower leg outward when the knee is bent. These muscles are essential for walking, running, jumping, and controlling gluteal movement, and they act as a brake against the quadriceps when slowing down knee extension.
In sports, hamstring injuries are common, especially from sprinting when the muscle is overstretched during the late swing phase of the leg. The injury rate in athletes and dancers is about two per 1,000 hours of performance, and in some sports, hamstring strains account for 19% of all injuries, leading to an average of 24 days lost from competition. The biceps femoris is the most frequently injured, followed by the semitendinosus; semimembranosus injuries are rare. Ultrasound or MRI can show the grade of strain and whether the muscle is fully torn, and a strain longer than 60 mm raises the risk of recurrence.
The distal semitendinosus tendon is sometimes used in ACL reconstruction surgery, where a piece of it replaces the anterior cruciate ligament, one of the four major ligaments in the knee.
- field
- Human anatomy
- known_for
- Flexion of the knee and extension of the hip; common running injury site
Lore & Background
The word "hamstring" combines an Old English term for the hollow or bend of the knee with a reference to the string-like tendons palpable on either side of the back of the knee. In human anatomy, the hamstrings are the three posterior thigh muscles situated between the hip and the knee: from the inner to the outer side of the leg, these are the semimembranosus, semitendinosus, and biceps femoris. A muscle is considered a true hamstring only if it meets four criteria: it originates from the ischial tuberosity, inserts over the knee joint into either the tibia or fibula, is innervated by the tibial branch of the sciatic nerve, and participates in both flexion of the knee and extension of the hip. The adductor magnus is sometimes grouped with the hamstrings because its degenerated tendon morphologically forms the tibial collateral ligament of the knee, which attaches near the adductor tubercle. All three true hamstrings cross both the hip and knee joints, making them biarticular muscles. They contract when the knee bends or the hip extends, and they lengthen when the knee straightens. The semitendinosus and semimembranosus extend the hip when the trunk is fixed, flex the knee, and medially rotate the lower leg when the knee is bent. The long head of the biceps femoris extends the hip, while both its heads flex the knee and laterally rotate the lower leg when the knee is bent. The short head of the biceps femoris crosses only the knee joint and is not involved in hip extension; due to its different origin and innervation, it is sometimes excluded from the hamstring group. These muscles are crucial for walking, running, and jumping, acting as antagonists to the quadriceps during the deceleration of knee extension.
Reader's Guide
The hamstrings are a group of three posterior thigh muscles—the semimembranosus, semitendinosus, and biceps femoris—that run between the hip and knee. The word "ham" originally referred to the hollow or bend of the knee, derived from Old English and Germanic roots meaning "crooked," while "string" denotes the tendons felt on either side of the back of the knee. True hamstrings share four defining features: they originate from the ischial tuberosity, insert over the knee joint onto the tibia or fibula, are innervated by the tibial branch of the sciatic nerve, and participate in both knee flexion and hip extension. The adductor magnus is sometimes included because its degenerated tendon forms the tibial collateral ligament. These biarticular muscles act on two joints: they contract when the knee bends or the hip extends, and lengthen when the knee straightens. Semitendinosus and semimembranosus extend the hip when the trunk is fixed, flex the knee, and medially rotate the lower leg. The long head of the biceps femoris extends the hip, while both heads flex the knee and laterally rotate the lower leg. The short head of the biceps femoris crosses only the knee and is not involved in hip extension, leading some to exclude it from the hamstring group. Hamstrings are crucial for walking, running, and jumping, acting as antagonists to the quadriceps during knee deceleration. In sports, hamstring injuries are common, with an incidence of about two per 1,000 hours of performance, and account for roughly 19% of all sports injuries, causing an average of 24 days lost from competition. The biceps femoris is most frequently injured, followed by semitendinosus; semimembranosus injury is rare. Imaging via ultrasound or MRI helps grade strains and assess retraction before surgery. The distal semitendinosus tendon is often used in ACL reconstruction to replace the anterior cruciate ligament.
Did You Know?
- The short head of the biceps femoris crosses only the knee joint and is sometimes excluded from the 'hamstring' characterization.
- A hamstring strain greater than 60 mm in length has a greater risk of recurrence.
- The adductor magnus is included among the hamstrings because the tibial collateral ligament is morphologically its degenerated tendon.
- The hamstrings are most important as an antagonist to the quadriceps in deceleration of knee extension during walking.
Frequently Asked Questions
What is Hamstring?
The hamstrings are a trio of muscles lining the back of the thigh, spanning from the hip region down to the knee. They form the primary posterior muscle group of the lower leg in human anatomy.
What are Hamstring's powers/role?
Because they cross both the hip and knee joints, they simultaneously handle knee flexion and hip extension. This dual-joint action makes them essential for walking, running, jumping, and everyday locomotion.
Who are Hamstring's members?
The group is made up of three muscles arranged from inner to outer thigh: the semimembranosus, the semitendinosus, and the biceps femoris. Together they act as a coordinated unit rather than three independent players.
Why is Hamstring a common running injury site?
Spanning two joints at once means they absorb and generate enormous force during sprinting, sudden stops, and explosive starts. That dual-joint mechanical load makes them especially prone to strains in runners and athletes.
How does Hamstring interact with the gluteus?
Beyond their core knee-bending and hip-extending duties, the hamstrings also help regulate certain movements of the gluteus region. This secondary role ties them into a broader posterior-chain network rather than letting them operate in isolation.
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