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The hamstring muscle group is comprised of three muscles: the biceps femoris, semitendinosus, and semimembranosus. These muscles are located in the posterior compartment of the thigh, running from the pelvis to the knee. They are responsible for various leg movements, including walking, climbing stairs, and running. Due to their function in these activities, hamstring injuries are common, especially among athletes who perform sudden stops, changes in direction, or a lot of jumping or squatting. Strains, tears, and pulls are among the most frequent hamstring injuries, with grades of severity ranging from mild to severe.
| Characteristics | Values |
|---|---|
| Location | Back of the thigh, starting at the pelvis and extending to the knee |
| Number of Muscles | 3 |
| Muscle Names | Biceps femoris, semitendinosus, semimembranosus |
| Muscle Functions | Extension and flexion of the hip and knee, rotation of the hip and knee |
| Muscle Structure | Long, elastic muscle fibres |
| Innervation | Sciatic nerve (L4-S3), tibial nerve, common peroneal branch of the sciatic nerve |
| Blood Supply | Inferior gluteal artery, perforating branches of the deep femoral artery |
| Susceptibility to Injury | High, especially in athletes who run, sprint, jump, or change directions |
| Common Injuries | Strains, pulls, tears, avulsion fractures |
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Biceps femoris
The biceps femoris is a muscle of the thigh located at the back, in the posterior compartment. It is one of the three muscles that comprise the hamstring muscle group, the other two being the semitendinosus and semimembranosus. The biceps femoris is located on the outside of the back of the thigh. It functions to flex the knee, extend the thigh at the hip, and rotate the lower leg from side to side when the knee is bent.
The biceps femoris has two heads: the long head and the short head. The long head is considered part of the hamstring muscle group, while the short head is sometimes excluded from this characterisation. This is because the short head only causes knee flexion and not hip extension, and it is activated by a different nerve—the peroneal nerve—as opposed to the tibial branch of the sciatic nerve, which activates the long head. The long head is the weaker knee flexor when the hip is extended and, likewise, is a weaker hip extender when the knee is flexed.
The biceps femoris muscle runs from the ischial tuberosity to the proximal part of the fibula, crossing the hip and knee joints. It acts on these joints simultaneously, producing hip extension and external rotation at the hip joint, and flexion and external rotation at the knee joint. The biceps femoris is the most lateral hamstring muscle located in the posterior thigh.
The biceps femoris is susceptible to injury, especially in athletes who run and sprint. Avulsion of the biceps femoris tendon is common in sports that require explosive bending of the knee, such as sprinting. A rare injury that can occur is snapping biceps femoris tendon, which is caused by subluxation or dislocation of the biceps femoris tendon, abnormal insertion of the tendon, or meniscal instability.
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Semitendinosus
The semitendinosus is one of three muscles that comprise the hamstrings, along with the semimembranosus and the biceps femoris. The semitendinosus muscle is located between the other two muscles at the back of the thigh. It is the longest muscle in the hamstring group, measuring an average of 44.3 cm.
The semitendinosus muscle is involved in flexing the knee and extending the hip. It also helps to medially rotate the tibia on the femur when the knee is flexed and medially rotate the femur when the hip is extended. It counteracts forward bending at the hips. The muscle is susceptible to injury, with strains and tears ranging from mild to severe. These injuries can occur as a result of sudden movements, overstretching, or overuse of the muscle during sports activities such as running, jumping, or sudden changes in direction.
The semitendinosus muscle receives its vascular supply from the profunda femoris artery, also known as the deep artery of the thigh. The perforating branches of this artery are responsible for the vascular supply of the muscle. The vascular drainage of the semitendinosus muscle is handled by the perforating veins of the profunda femoris vein, which drains into the femoral vein.
The semitendinosus muscle shares close insertion and attachment points with the semimembranosus muscle. At its insertion, the semitendinosus gives off a prolongation to the deep fascia of the leg and lies behind the tendon of the sartorius and gracilis muscles, with which it forms the Pes Anserinus, named for its resemblance to a webbed "goose's foot." The semitendinosus tendon has been used in anterior cruciate ligament reconstruction, either as a tendon double-bundle or quadruple-bundle technique.
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Semimembranosus
The semimembranosus muscle is one of the three muscles that comprise the hamstrings, along with the semitendinosus and the biceps femoris. It is located on the innermost side of the back of the thigh, extending from the hip to the knee. It is a relatively long and large muscle.
The semimembranosus is responsible for extending the hip joint and flexing the knee joint. It also helps to medially rotate the knee and femur. This muscle works in conjunction with the other hamstring muscles to perform its functions. The hamstrings play a crucial role in various human activities, from walking and running to more explosive actions like sprinting and jumping.
The semimembranosus is deep to the semitendinosus muscle and is situated at the back and medial side of the thigh. It is wider, flatter, and deeper than the semitendinosus. The muscle begins as a flat and membranous structure that develops a fleshy belly about midway down the thigh. The semimembranosus is also superficial to the adductor magnus and medial to the biceps femoris.
The semimembranosus muscle has a unique structure that aids in its identification. Its tendon trifurcates distally, giving rise to three distinct parts. The first part inserts on the medial tibial condyle, the second part fuses with the popliteal fascia, and the third part forms the oblique popliteal ligament. The lateral border of the semimembranosus forms the superomedial wall of the popliteal fossa.
The semimembranosus muscle is innervated by the L5, S1, and S2 nerve roots, which access the muscle through the tibial division of the sciatic nerve. The femoral and popliteal arteries supply the semimembranosus muscle with deep perforating branches, and occasionally, the inferior gluteal artery supplies its proximal part.
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Hamstring injuries
The hamstrings are comprised of three muscles: the biceps femoris, semitendinosus, and semimembranosus. They are skeletal muscles at the back of the thigh, starting at the pelvis and extending to the knee. They are used for walking, climbing stairs, running, jumping, and many other leg movements.
Due to their function, hamstring muscles are susceptible to injury, especially in athletes who sprint, jump, climb, or lunge. Hamstring injuries are the most common sports injury. They are caused by muscle overload, where the muscle is stretched beyond its capacity, or suddenly loaded with weight. This can lead to a strain, or "pulled hamstring", where the muscle fibres overstretch or tear. The injury can range from mild, with very little torn muscle, to severe, where the muscle tears completely away from the tendon or bone.
The symptoms of a hamstring injury include a bump or knot in the muscle, pain, swelling, and a loss of strength in the affected hamstring. Treatment includes rest, ice, compression, elevation, and gentle stretching, with recovery times ranging from a few days to a few months, depending on the severity of the injury.
To prevent hamstring injuries, it is important to stretch, warm up, and avoid pushing through pain in the hip, knee, and leg.
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Hamstring functions
The hamstrings are a group of three long muscles located in the posterior compartment of the thigh. They are the biceps femoris, semitendinosus, and semimembranosus. The hamstrings have several important functions, including:
Flexing the knee joint
The primary function of the hamstrings is to flex the knee joint, allowing for movements such as running, jumping, and climbing. The biceps femoris, in particular, is responsible for flexing the knee, extending the thigh at the hip, and rotating the lower leg from side to side when the knee is bent.
Extending the hip
The hamstrings also play a crucial role in extending the hip, which is essential for maintaining an erect posture when standing or walking. The semimembranosus, specifically, helps to extend the hip and bring the trunk into an erect position when the foot is firmly planted on the ground.
Stabilizing the knee and hip joints
The hamstrings also have an important stabilizing function. They work together with the collateral ligaments to stabilize the knee joint and protect it from injury. Additionally, they help to stabilize the hip joint by counteracting tilting movements and preventing falls.
Gait cycle
The hamstrings play a significant role in the gait cycle, which is the complex movement pattern involved in walking. During the swing phase of walking, the hamstrings decelerate the forward motion of the tibia, absorb kinetic energy, and protect the knee and hip joints.
Other leg movements
The hamstrings are involved in a wide range of leg movements, including squats, stair climbing, and sprinting. They enable these movements by working in tandem with other muscles, such as the quadriceps and anterior cruciate ligament (ACL).
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Frequently asked questions
The hamstrings are made up of three muscles: the biceps femoris, semitendinosus, and semimembranosus.
The hamstrings are located at the back of the thigh, running from the pelvis to the knee.
The hamstrings are involved in various leg movements, including walking, climbing stairs, running, and jumping. They also help to stabilise the knee joint and protect the knee and hip joints during walking.
The hamstring muscles extend the hip and flex the knee. They also play a role in rotating the lower leg from side to side.
Yes, hamstring injuries are very common, especially in athletes who run, sprint, or perform sudden stops and turns. Hamstring strains can range from mild overstretching to severe tears.
