A Transcutaneous Electrical Nerve Stimulation machine is a remarkable device which can help remove backache extremely effectively at very low cost and with few side effects. To understand how it works it would be best to explain how your body recognises pain.

The gate control theory of pain put forward by two scientists called Melzack and Wall suggested that when body tissues are damaged, messages carrying information about the injury travel towards the brain along two quite separate sets of nerve fibres. The larger fibres carry messages about sensations other than pain, and the smaller fibres carry the pain messages. The messages which travel along the larger fibres tend to arrive at the spinal cord before the messages travelling along the smaller fibres and, if there are enough non painful sensations travelling, the pain messages won't be able to get through to the brain.

Once this theory had been accepted it was possible to explain all sorts of natural phenomena which had, up until then, been a mystery.

So, for example, it became clear that when we rub a sore spot what we are doing is increasing the number of non-pain messages travelling towards the spinal cord (and thence the brain). If you knock your elbow you will automatically reach to rub the spot because sub-consciously you know that by rubbing the area you will be able to cut down the amount of pain that you feel.

Having realized just how rubbing a sore or painful place can relieve pain, the next step for scientists was to come up with the idea of using electrical pulses to produce the necessary stimulus.

When the theory was first put into practice in the late 1960s doctors suggested that electricity should be introduced into the body through electrodes surgically implanted in the spine. Although that did work, the fact that it involved an operation limited the usefulness and availability of the procedure.

Next, it was discovered that all nerves within an inch or so of the surface of the skin can be stimulated by electrodes which are simply stuck onto the skin. That encouraged medical researchers to start giving patients pocket-sized battery-operated stimulators which sent out a continous series of electrical pulses which could transmit those pulses into the large nerves of the body via silicon electrodes stuck to the skin with a special conducting paste. It worked!

More exciting still, it was discovered that Transcutaneous Electrical Nerve Stimulation (TENS) did not just stimulate the passage of sensory impulses designed to inhibit the passage of pain impulses; it also stimulated the body to start producing its own pain-relieving hormones known as endorphins.

During the last ten years an enormous number of research projects have shown that TENS machines are convenient, safe and effective. They are also cheap to buy and extremely cheap to run.

TENS machines have been shown to be effective in the treatment of all kinds of pain. For example, a Swedish study has shown that TENS machines are the only painkillers required by 70 per cent of women in labour; and backache is one of the types of pain best treated with TENS machines.

With this sort of success available from a small, cheap, portable, long-lasting machine that can be used at home without any training and that does not seem to produce any side effects at all, you might imagine that doctors would be recommending TENS machines to millions of patients and that shops would have different models stocked high on their shelves. But if you try to buy a TENS machine you'll have difficulty. This problem lays squarely at the door of the drug companies who don't want patients in pain to be able to deal with their symptoms so easily, quickly and cheaply. Drug companies make huge amounts of money out of selling painkillers to pain sufferers and if people used TENS machines instead it would cost them a fortune in lost sales.

If you want to try a TENS machine ask your doctor to refer you to the nearest pain clinic. You should be able to get one on loan and if you find that the machine works for you then you should be able to obtain one for permanent use.