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The hamstring

Hadyn Luke posted this on Tuesday 23rd of April 2013 Hadyn Luke 23/04/2013

Tags: Anatomy and physiology


The hamstring

Our blog today looks at the hamstring: where it’s located and how it works.

The hamstring is a large muscle group at the back of the upper thigh, running from the medial to the lateral head. It consists of three muscles: 

  • semitendinosus
  • semimembranosus
  • biceps femoris

As the hamstring is a major muscle group, it’s useful for a personal trainer or fitness instructor to understand how it moves and which exercises or sports particularly rely on the action of the hamstring.

The origination and insertion of the hamstring

The origination of the hamstring is at the back of the ischial tuberosity, more commonly known as the sitting bone, at the top of the femoral head. The biceps femoris also originates from the back of the femur. 

The insertion of the semimembranosus, which runs down the inner back of the thigh, is at the back of the medial condyle of the tibia. The semitendinosus inserts into the upper medial surface of the shaft of the tibia. Finally, the biceps femoris inserts into the head of the fibula and the lateral condyle of the tibia. 

The action of the hamstring

The hamstring is involved in knee flexion, for example when a personal trainer asks a client to keep their thigh straight and bend their knee in a standing position, and it is also used in hip extension.

The semimembranosus and the semitendinosus also medially rotate, allowing the leg to turn inwards when the knee is flexed (bent). The biceps femoris laterally rotates, turning the lower leg outwards when the knee is flexed. 

The hamstring and sciatica

The hamstring links to the sciatic nerve (L4, L5, S1, S2 and S3), which is why people with sciatica can often feel pain travelling down their legs. 

Basic functional movement

A personal trainer may find that clients who do a lot of running get tight hamstrings, as the muscle group acts to slow down the leg at the end of the forward swing and also stops the trunk from flexing at the hip joint. 

Other sports that rely heavily on the movement and strength of the hamstring include sprinting, hurdling and football (especially back kicks), as well as activities that require jumping. Weightlifters will use the upper portion of the hamstring in particular. 

The hamstring can be worked in isolation on a leg curl machine or a multi-hip machine, which also uses the gluts. However, if a personal trainer is setting an exercise routine using gym equipment such as the treadmill, cross trainer or rowing machine, their client will be working their hamstrings with a range of other muscles as part of the exercise.

Injuries to the hamstring

These are most commonly caused by a sudden lengthening of the muscle, such as a forward kick or doing the splits. A fitness instructor or sports trainer should always ensure that their clients or team members are sufficiently warmed up prior to carrying out these activities in order to avoid such injuries. 

Footballers and runners often need sports therapy or massage to heal or prevent injury to the hamstrings. 

Problems arising from tight hamstrings

Some personal trainers use PNF stretching (see our blog on How a personal trainer can apply pnf stretching) with their clients. Generally, the client should be able to lift their leg to an angle of 80° or 90°; if they can’t, this suggests that they are suffering from tight hamstrings.

If a personal trainer or other fitness professional is working with a client or athlete whose muscles are chronically tight, they may also be suffering from lower back pain, knee pain, discrepancies in leg length and restrictions when they are trying to walk or run. 

With the hip flexor complex (see our blog on The hip flexor complex), a tight psoas major can cause anterior pelvic tilt. However, if the hamstring is too tight it can cause posterior pelvic tilt, which can lead to kyphosis in the upper spine. 

As the hamstrings are in a shortened state when we are seated, if a personal trainer is working with a client who spends a lot of time sitting at a desk, for example, they may find that their hamstrings become tight over time and need extra work.


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