Feb 2015 28

The hamstrings

By: Dave Wheeler

Last month I blogged about the quadriceps (the muscles at the front of the thigh). In this week's blog we'll look at those on the back - the hamstrings.


pic @ wikimedia.org


The actions of the hamstrings

The main action of the hamstrings is to bend the knee. They do this by pulling up the lower leg behind you.

There are 3 hamstrings, all of which start out at the ischial tuberosity (the bony bit at the base of your bum) and attach to the bones of the lower leg.


  • Semimembranosus is shown in the diagram in green - it's a broad flat muscle on the at the back of the leg lying towards the inside of the body.
  • Semitendinosus (in blue) is a thinner muscle that lies superficial to, and on top of, the semimembranosus 
  • Biceps femoris (shown in red) runs down the back of the leg, towards the outside.


Semimembranosus and semitendinosus connect to the back of the tibia (the main leg bone).

Biceps femoris connects to the back of the fibula (the smaller, outer leg bone).

So when the hamstrings contract together, they pull the lower leg up - that is, the knee bends.

But that's not the only possible action: if the knee remains straight and the hamstrings contract, then the back of the pelvis will be pulled down backwards (because they connect to the ischial tuberosity).


The other function of the hamstrings - shock absorbers

Like the other muscles of the leg, one of the major functions of the hamstrings is to absorb the shock from running.

With every footstep that you take when walking, 1½ times the force of your body weight spirals up your leg. So if you weigh 80kg (about 12½ stone) then 120,000 Newtons of force go spiralling up your body with every step. 

If you run, then the amount of force spiralling up the leg with every stride goes up to twice the weight of your body.

The joints of the knee, hip and lower back are all protected by these shock absorbers. But this only works optimally if you have what's called the neutral posture.

These days the majority of people in the UK have a posture associated with hips tilted backwards (flat back or sway back). Remembering the attachment points of the hamstrings, if the hip is tilted backwards then the hamstrings will be kept in a permanently shortened position. In other words, they'll always be tight.

When the muscles are hypertonic like this, there's not much springiness in them, so they don't do their job of absorbing shock properly.


Treating tight hamstrings

Tight hamstrings can be treated with a number of different therapies:


As ever, if you think I can help, give me a call.