How to use a Tens Machine
This article addresses how a TENS is thought to work and how best to use the machine for pain management
How TENS Is Thought To Work
Conventional TENS relieves pain by having a direct effect on the pathway the pain is taking into the central nervous system. It reduces the sensitivity of the cells which transmit the pain onwards up towards the brain. Stimulation by TENS of the large non-pain nerves can reduce the activity of the pain transmitting cells for two hours.
More intense TENS stimulates the small pain-transmitting nerves, causing activation of the inhibitory mechanisms from other areas of the nervous system. It also tends to block nerve impulses going along a nerve in a sort of “busy telephone line” effect. All the pain and all the TENS cannot get along the nerve, reducing the amount of pain signals which can get through.
When TENS signals enter the nerves, they travel both ways, up to the spinal cord and down to where the nerves start in the bodily tissue that is painful. These impulses collide with upcoming pain impulses and knock them out, reducing the total pain which gets through.
How To Use TENS
It is useful for you to have a pain assessment before you start TENS. That way we can find out what kind of pain you have and exactly where it is. If you have numb areas on your skin for example, these will need to be avoided as TENS needs an intact nerve pathway to work.
Two channel (four electrode) machines are more flexible especially if the pain is large or widespread.
- Start with conventional TENS with a continuous pulse setting.
- Use middle pulse frequency(approx 80-100 per second) and pulse duration (100-200 microseconds).
- Turn it up slowly until you can feel it, then gradually up it is strong and a bit uncomfortable, then turn it down slightly so it’s comfy.
- You may need to experiment with the settings as there is no sure way of telling which combination will suit you without trial and error.
- Put the electrodes on normal healthy skin. Check to make sure you don’t have any cuts or other breaks in the skin which could be very uncomfortable and react badly.
- Take time to find the best electrode placement – this may be tricky.
Don’t use over hypersensitive areas which are painful to very minor stimuli. This can make the pain worse.
Avoid areas of reduced skin sensation as it’s not effective and you may turn it up too much as you can’t feel the intensity accurately.
If you can’t place the electrodes over the skin area which relates to the nerve thought to be causing pain, you can place them along the nerve tracks. Diagrams are available to guide good placement.
Areas NOT To Put Electrodes
- Don’t put them over the front of the neck as this can cause low blood pressure or spasm in the larynx.
- Don’t put them over the eyes (you weren’t going to, were you?) as this can increase the pressure in the eyes.
- Avoid putting them back and front through the chest, as stimulation here will go right through the heart and could affect its activity.
- Don’t use it internally unless you have a specific device designed for this, and guidance in use.
You will notice there are often red and black leads with TENS machines. It makes no difference which way round you use them.
Working Out the Electrical Aspects of TENS
The intensity of the stimulation is the most important aspect of treatment because it determines which types of nerve get affected. You need to work up the intensity until you get the result you are looking for:
- Non-painful pins and needles means the large, non-pain nerves are stimulated.
- Painful pins and needles means the small skin sensation nerves are stimulated.
- Muscle twitching means the small nerves coming from muscle are being affected.
Research has not clarified which combination of electrical settings needs to be used for any particular type of pain. Trial and error is needed to establish the best settings for you within your comfort.
How Long To Use TENS and What Dose
Conventional TENS tends to have its pain-relieving effect very quickly, and lose its effect very quickly when the stimulation is turned off. People vary widely in how much post-TENS pain-relieving effect they report after treatment and the reason for this is not clear.
Higher intensities of treatment could result in longer term effects. The nervous system can get used to TENS over the long term (habituation) and lead to poorer pain control. If you stop using TENS for a while this can help, as can changing the electrode positions or the electrical settings.
Things to Be Wary Of With TENS
TENS is a very safe treatment, but there are some things to be aware of. From a legal point of view treatment in the presence of a heart pacemaker, pregnancy or epilepsy may be unwise. Consult a specialist in these matters because treatment may still be possible.
As for all electrical stimulations, TENS should not be applied over a known tumour without specialist advice.
It is unusual to have any severe reaction from TENS. Skin irritation under the electrodes can be quite troublesome so it’s important to remove the electrodes every day and wash the skin areas carefully. Moving the electrodes slightly to new areas of skin may also be sensible if you are sensitive.
Some people feel faint or report nausea and some of my patients have said that TENS makes their pain worse and so they stop using it. TENS can be left on for long periods but if you are asleep and unable to monitor skin sensations, it might be best to take it off or use a timer which automatically does so after a time.
The Usefulness of TENS
Our patients tell us that TENS is useful in their pain control but the scientific backing for this is not so good, as many research trials are not of good quality. This means we can’t rely on their findings.
TENS may be useful in acute (recent) pains but has been found to be helpful in many types of chronic (long-term) pain, especially musculo-skeletal problems.