The closely related muscles at the back of the thigh, just below the buttock and above the knee, are called the hamstrings (from Anglo-Saxon: haum—'haunch' and Latin stringere—'to draw together'). This muscle group helps to flex the knee joint (aided by the gracilis and the sartorius) and extend the hip joint. When the knee is in a flexed position, they also aid in rotating the lower leg. While running, the hamstrings serve as a braking mechanism for the leg at the end of its forward swing, also keeping the trunk straight in the bargain.

The three muscles that make up the hamstrings group are:

  • Semimembranosus (TA: musculus semimembranosus)—the most medial (located nearer the inside of the thigh), is named for its membranous tendon of origin.
  • Semitendinosus (TA: musculus semitendinosus)—situated between the other two muscles, is so-called because of its very long tendon. The semitendinosus muscle is on the middle of the back of the thigh.
  • Biceps femorus (TA: musculus biceps femorus)—the most lateral (outside), this muscle runs along the outer portion of the back of the thigh.

All three muscles run past the knee joint. The name biceps means 'two heads' and the biceps femoris could almost be considered as two separate muscles. Its long head originates on the ischial tuberosity (the "sit bones")—as do the other two muscles. The short head of the biceps femoris originates on the back of the femur (the linea aspera). Both the semimembranosus and semitendinosus insert on the medial (inner) portion of the upper tibia. The biceps femoris inserts both on the head of the fibula and on the lateral condyle (the upper outside portion) of the tibia.

The hamstring muscles are attached to branches of the sciatic nerve (L4, 5, S1, 2, 3), the long head of the biceps femoris is attached to the common peroneal nerve (L4,5, S1, 2). The muscles receive blood supply from perforating branches of the deep femoral artery.

Hamstring Strain

Athletic events which place a great deal of mechanical stress on the hamstrings may lead to the tearing or rupturing of the muscle fibres. Among runners (especially sprinters), jumpers and soccer players, strain of the hamstrings is not an uncommon injury. Hamstring strain is most common near the proximal (top) attachment and most frequently occurs when the muscle is subjected to tensile (pulling) stress during contraction.

Strains range in severity from first degree (slight) to third degree (severe). A third degree hamstring strain may sometimes include an avulsion fracture, an extremely painful and debilitating injury wherein a tendon is pulled away from its anchor point, breaking loose a piece of bone with it.

Hamstring strains usually occur when the muscles are subjected to sudden, extreme loading without proper warmup and stretching. One factor which may contribute to the likelihood of a hamstring strain is a strength imbalance between the hamstrings and quadriceps (the muscles of the front of the thigh, usually much stronger than the hamstrings). Chronic tightness in these muscles can also contribute to the chances of injury.

Mild hamstring strain is usually treated in the same way as the minor strain of almost any muscle in the body—physical therapists use the acronym PRICE: protection, rest, ice, compression, elevation. Simply put, wrap it up (Ace bandages work well), keep it elevated, keep it cool, avoid further irritating it. Stretching and massage are also usually helpful. More severe strains may require anti-inflammatory drugs, physical therapy and (in the most extreme cases), surgery.

Hamstring Care and Maintenance

As with most muscles, the stretching and strengthening of the hamstrings can be crucial to preventing injury.

To stretch the muscle group, lie flat on your back (supine) and lift one leg. Place a towel or strap over the sole of that foot and actively straighten the leg. Alternately, lie in a doorway and place the lifted leg against the door jamb, then press by contracting the hamstrings. Either of these two is a very good stretch for these muscles.

Another excellent way to stretch the hamstrings is as follows: stand with your feet apart (at least shoulder width), bend at the waist so that your fingers can touch the ground (for persons who are particularly inflexible, this may take some finesse). This stretches the gluteal group and, to a small extent, the hamstrings. Now bend the knees slightly—this stretches the hamstrings more. Now, slowly, "walk" your fingers toward one foot or the other. You should feel a fairly profound stretch in the medial (inner thigh) portion of the hamstring muscles. Hold this stretch for at least a count of 20. Repeat this stretch on the other side.

Several sports and exercises are good for strengthening these muscles: sprinting, soccer, jumping, hurdles, and distance running, to name a few. Any game which features a large amount of dashing about (such as tennis and basketball) is good for building the hamstrings. A hip exercise machine or leg curls can also provide good strengthening exercise for these muscles.

Hamstring: The Word

At one time, the term hamstrings was commonly used to refer to the proximal (upper) tendons of these muscles (as well as the nearby gracilis). This usage was more common in the past and currently the term is almost exclusively used to refer to the muscles.

Hamstring may also be used as a (transitive) verb. To hamstring something or someone is (literally) to cut the hamstrings with a sharp blade—a highly effective method of laming an animal (or a human). The word is usually used figuratively to refer to something being badly hindered, perhaps in a way which is permanent or fairly difficult to overcome: The team's chances of competing in the playoffs were badly hamstrung by the loss of their entire coaching staff.


References:
Jarmey, Chris, "The Concise Book of Muscles" (Lotus Publishing, Chichester, England, 2003).
Lowe, Whitney, "Hamstring Strain" Massage Magazine, May/June 2005, pp. 116-120.
Taber's Cyclopedic Medical Dictionary, 19th Edition (FA Davis, Philadelphia, 1997).
Gray, Henry, Gray's Anatomy, revised 15th American edition (Bounty Books, New York, 1977).
Kapit, Wynn, and Elson, Lawrence M. "the Anatomy Coloring Book" second ed. (Addison Wesley, New York, 1993).
Lecture 4: medial and posterior compartments (of the leg). On line at: https://netfiles.uiuc.edu/jdpolk/www/anatomy/Lower_Limb_Lecture_4.pdf
Special thanks to Rodney Williams, massage therapist and personal trainer extraordinaire, for stretching info.

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