This article was originally published in Positive Health issue 73 – February 2002
According to the dictionary, a hamstring “in humans, apes, etc.,” consists of “each of the five tendons at the back of the knee”. But who pulls the strings? It is the hamstring muscles that pull on three of them. They would be better described as ‘hamropes’ or ‘hamwires’, for they are usually very tough and tight muscles. From the word hamstring we get the verb (now rare) hamstrung or hamstringed meaning “to lame or disable by cutting the hamstrings”. It is also used in the figurative sense as in “to destroy the activity or efficiency of”. Tight hamstring muscles do just that – they interfere with the efficient functioning of the body.
To belong to the hamstring group, a muscle must arise from the ischial tuberosity or sitting bone, pass over the knee joint to be inserted into the tibia or fibula, and be supplied by the sciatic nerve. Three muscles fulfil all of these conditions: the semitendinosus, the semimembranosus and the biceps femoris (except its short head). Note that they cross two joints and have an action on both. Muscles that act in this way are called bi-articular or two-joint muscles. Unlike mono-articular muscles, which cross only one joint and can have only one action on this joint, bi-articular muscles can have two or three actions. Thus, the hamstring muscles extend (postero-flex would be more accurate) the hip joint, flex the knee joint, and rotate the hip and knee joints. They even play a role in ADDuction. The bi-articular notion should always be taken into account during any form of physical therapy or body training; however it is, unfortunately, often overlooked.
We admitted three muscles into the hamstring group, yet there is another muscle, or part of a muscle, that is a candidate to join the club – a fourth hamstring! The ADDuctor magnus, a big muscle that lies in the inner side of your thighs, is a composite or hybrid muscle made of three distinct parts. The third and more vertical part, in common with the hamstrings, is supplied by the sciatic nerve and arises from the ischial tuberosity. Just to confuse the layman, this ‘fourth hamstring’ is sometimes called the ‘third adductor’. I don’t want to appear too finicky but it is difficult to decide if the ‘fourth hamstring’ should really belong in this group because it fails on one important count: it does not cross the knee joint; in other words, it is not a bi-articular muscle. So I leave it to you whether you prefer to have three or four hamstring muscles. If you want my advice, it’s best not to be greedy – three is quite sufficient.
This just goes to show that anatomy is not an exact science. Even with the aid of electromyography, it is still difficult, with some muscles, to know precisely what does what. Consult several anatomy books and you will often find disagreement on seemingly simple muscle action. You might also find some information that is just not true. Here are two examples that concern the hamstring muscles: the quadriceps muscle, covering the front of your thighs, is said to be about three times as strong as the hamstrings. Yet, clinical experience shows that the quadriceps is no match for the hamstrings. Test it on yourself, sit on the floor with your legs joined together and extended (long-sitting). Now, with the help of a mirror at your side to check your alignment, try to straighten your back. This is practically impossible with short hamstrings (a condition that applies to most of us) because they tilt the pelvis backwards. In order not to fall in the same direction, the upper body is forced to bend forwards. This results in a seriously slouched posture. If you make a Herculean effort to straighten yourself, your knees are likely to bend, still under the influence of the hamstrings, and if you manage to hold the correct posture it won’t take long before the quadriceps muscle cramps up. It may be three times stronger than the hamstrings but it is definitely unfit and always ends up the loser in a contest with its antagonists. This is mainly due to the fact that the hamstrings are bi-articular muscles, which belong to a long chain of muscles running from head to toe. In this muscular system its strength is derived from the sum of all the muscles belonging to it. If you are curious to see a graphic representation of the overlapping nature of muscles that constitute a muscular chain, open an anatomy book and look for a picture of the politeal fossa (the back of the knee). You will clearly see how the tendons of the hamstring muscles overlap those of the gastrocnemius.
The rotations of the femur provide us with the second example. Classically, the external rotators of the femur are said to be more numerous and stronger than the internal ones. Yet, in most cases of abnormality, the knees are turned inwards. The straight-leg-raising test clearly illustrates this situation: if you lift the legs of someone in a supine position until the legs are perpendicular to the floor you will find that in most cases the knees will flex under the influence of the hamstrings. If you then ask the person tested to extend the knees fully you will now see that the knees have turned inwards. This is because two of the hamstring muscles are powerful inward rotators.
The inward rotation of the knees has been substituted for the suppressed flexion. Only bi-articular muscles can perform such stretch-avoidance behaviour. Moral: don’t believe everything that is written in textbooks!
The hamstring muscles shorten very easily. Sitting all day long in a slouched position is an important cause of that shortening. Once shortened, they impede normal movement of the hip joint and, for this reason, can be responsible for lower back pain; they also give rise to bow legs, knock-knees, flat feet, hollow feet, etc., and give a lot of grief to the owners of these legs.
It is therefore important to maintain or restore normal elasticity to the hamstrings. You just need to learn the ropes – all the ropes, since they are closely knitted in a long band that extends from head to toe.