Hello Surgeon

X

How can we help you today?

Post

Hamstring Muscles

The Hamstring Muscles consist of three muscles: biceps femoris, semitendinosus, and semimembranosus. These muscles are the posterior thigh muscles. 

The Hamstring muscles received their name because it is common to tie hams (pork thighs) up for curing and/or smoking using the long tendons of these muscles. This also explains the expression “hamstringing the enemy” by slashing these tendons lateral and medial to the knees.

The two actions of the Hamstring muscles cannot be performed maximally at the same time. Full flexion of the knee requires so much shortening of the hamstrings that they cannot provide the additional contraction that would be necessary for simultaneous full extension of the thigh. Similarly, full extension of the hip shortens the hamstrings so they cannot further contract to act fully on the knee.

When the thighs and legs are fixed, the Hamstring muscles can help extend the trunk at the hip joint. The hamstrings are active in thigh extension under all situations except full flexion of the knee, including maintenance of the relaxed standing posture (standing at ease).

A person with paralyzed Hamstring muscles tends to fall forward because the gluteus maximus muscles cannot maintain the necessary muscle tone to stand straight. The Hamstring muscles are the hip extensors involved in walking on flat ground, when the gluteus maximus demonstrates minimal activity. However, rather than producing either hip extension or knee flexion per se during normal walking, the hamstrings demonstrate most activity when they are eccentrically contracting, resisting (decelerating) hip flexion and knee extension during terminal swing (between midswing and heel strike).

The length of the Hamstring muscles varies, but this is usually a matter of conditioning. In some people, they are not long enough to allow them to touch their toes when the knees are extended. Routine stretch exercise can lengthen these muscles and tendons.

The hamstring muscles share the following common features (except the short head of the biceps):

  1. Proximal attachment to the ischial tuberosity deep to the gluteus maximus.
  2. Distal attachment to the bones of the leg.
  3. Thus, they span and act on two joints, producing extension at the hip joint and flexion at the knee joint.
  4. Innervation by the tibial division of the sciatic nerve.
See Also: Hamstring Strain
Hamstring Muscles anatomy

Hamstring Muscles

Semitendinosus Muscle

The semitendinosus, as its name indicates, is half tendinous. It has a fusiform belly that is usually interrupted by a tendinous intersection and a long, cord-like tendon that begins approximately two thirds of the way down the thigh. Distally, the tendon attaches to the medial surface of the superior part of the tibia as part of the pes anserinus formation in conjunction with the tendinous insertions of the sartorius and gracilis.

semitendinosus

Semimembranosus Muscle

The semimembranosus is a broad muscle that is also aptly named because of the flattened membranous form of its proximal attachment to the ischial tuberosity. The tendon of the semimembranosus forms around the middle of the thigh and descends to the posterior part of the medial condyle of the tibia.

The semimembranosus tendon divides distally into three parts:

  1. a direct attachment to the posterior aspect of the medial tibial condyle,
  2. a part that blends with the popliteal fascia,
  3. a reflected part that reinforces the intercondylar part of the joint capsule of the knee as the oblique popliteal ligament.

When the knee is flexed to 90°, the tendons of the medial hamstrings or “semi-” muscles (semitendinosus and semimembranosus) pass to the medial side of the tibia. In this position, contraction of the medial Hamstring muscles (and of synergists including the gracilis, sartorius, and popliteus) produces a limited amount (about 10°) of medial rotation of the tibia at the knee. The two medial Hamstring are not as active as the lateral hamstring, the biceps femoris, which is the “workhorse” of extension at the hip.

semimembranosus

Biceps Femoris Muscle

The fusiform biceps femoris, as its name indicates, has two heads: a long head and a short head. In the inferior part of the thigh, the long head becomes tendinous and is joined by the short head. The rounded common tendon of these heads attaches to the head of the fibula and can easily be seen and felt as it passes the knee, especially when the knee is flexed against resistance.

The long head of the biceps femoris crosses and provides protection for the sciatic nerve after it descends from the gluteal region into the posterior aspect of the thigh. When the sciatic nerve divides into its terminal branches, the lateral branch (common fibular nerve) continues this relationship, running with the biceps tendon.

The short head of the biceps femoris arises from the lateral lip of the inferior third of the linea aspera and supracondylar ridge of the femur. Whereas the hamstrings have a common nerve supply from the tibial division of the sciatic nerve, the short head of the biceps is innervated by the fibular division. Because each of the two heads of the biceps femoris has a different nerve supply, a wound in the posterior thigh with nerve injury may paralyze one head and not the other.

When the knee is flexed to 90°, the tendons of the lateral Hamstring muscles (biceps), as well as the iliotibial tract, pass to the lateral side of the tibia. In this position, contraction of the biceps and tensor fasciae latae produces about 40° lateral rotation of the tibia at the knee. Rotation of the flexed knee is especially important in snow skiing.

Biceps Femoris Muscle

References & More

  1. Anderson TB, Vilella RC. Anatomy, Bony Pelvis and Lower Limb: Posterior Thigh. [Updated 2023 Jul 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK554598/
  2. Clinically Oriented Anatomy, 8th Edition (2017).
Last Reviewed
December 29, 2023
Contributed by
OrthoFixar

Orthofixar does not endorse any treatments, procedures, products, or physicians referenced herein. This information is provided as an educational service and is not intended to serve as medical advice.

Angle Meter App for Android & iOS
  • Lifetime product updates
  • Install on one device
  • Lifetime product support
One-Click Purchase
Orthopedic FRCS VIVAs Quiz
  • Lifetime product updates
  • Install on one device
  • Lifetime product support
One-Click Purchase
Top 12 Best Free Orthopedic Apps
  • Lifetime product updates
  • Install on one device
  • Lifetime product support
One-Click Purchase
All-in-one Orthopedic App
  • Lifetime product updates
  • Install on one device
  • Lifetime product support
One-Click Purchase