TENS and Pain Relief

Whilst there have been numerous studies into how effective a TENS machine is, the results are mixed and confusing, they do appear to assist in alleviating pain for some people but they are less effective for others.

For example a 2008 research review indicated that
'Published literature on the subject lacks the methodological rigour or robust reporting needed to make confident assessments of the role of TENS in chronic pain management. Large multi-centre randomised control trials of TENS in chronic pain are still needed' (1)

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TENS stands for Transcutaneous Electrical Nerve Stimulation and uses low voltage electrical currents to relieve pain. The small electrical current is passed through electrodes, taped onto the skin near the site of the pain or injury. The current is normally generated from battery-operated machines. Since the machines are normally very portable and easy to use, pain sufferer do find them convenient and easy to use at home. If used then there will be tingling sensation on the skin where the electrodes are placed which some people find slightly unpleasant. Other than this there are no reported side effects from using a TENS machine.

It is hypothesised that TENS machines influence the way that pain signals are transmitted to the brain. The brain receives pain signals through the nervous system and if the pain signals can be blocked then the brain is likely to obtain fewer signals from the source of the pain and the outcome is that the sufferer feels less pain. In the Gate Control theory of pain, in the spinal cord the nerve fibres face a gate-like mechanisms that open and close to prevent or permit signals from then travelling on to the brain. If the gate is open, then the pain signal travels to the brain, pain is registered and we perceive the pain.

There are two ways in which TENS machines are claimed to work. Firstly, if the TENS machine is used on a high pulse rate of between 90-130Hz it will trigger the gate to close and this in turn is thought to block the pain nerve path to the brain. This appears to be the usual use of the TENS machine. However, if the machine is used on a low pulse rate around 3 - 5Hz then it may stimulate the patients body into making its own endorphins which are pain reducing chemicals which block the pain signals to the brain.

Another more recent hypothesis is that it may be TENS may assist in reducing pain by helping you believe that you have control over spontaneous muscle contractions, it may help you to feel less anxiety, and it also can merely provide a distraction from the muscular contractions.

What types of pain do people use TENS used for and how effective is it at reducing pain?
The machines are used by people to treat numerous acute and chronic pain conditions and injuries. They can either purchase or hire the tens machine. The injuries treated include lower back pain, neck pain, osteoarthritis, rheumatoid arthritis, sciatica, fibromyalgia, tennis elbow, pain during childbirth, etc. To have any chance of being effective then the electrodes should be placed close to the source of the pain. Some pain sufferers find that they only obtain relief while the TENS unit is operating on them. Others believe that pain relief continues after their treatment has finished.

Precautions
It is suggested that you do not use a TENS

• if you are fitted with a pacemaker;
• if you suffer from epilepsy and you are using the TENS machine alone;
• if you are in your first trimester of pregnancy;
• over the front of the neck or over your face;
• over any area of broken skin; and
• if you have some type of hearing implants.

You must always check with your doctor or physiotherapist if you are considering using a TENS.

(1) Nnoaham KE, Kumbang J; Transcutaneous electrical nerve stimulation (TENS) for chronic pain. Cochrane Database Syst Rev. 2008 Jul 16;(3):CD003222.

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