What Does a TENS Machine Do?

Are TENS Machines Just Another Fancy Idea or Do They Really Work?

The Short Answer –

A Transcutaneous Electrical Nerve Stimulation Machine (commonly known as a TENS unit) is a battery operated device that uses pads to transmit small electrical pulses to areas of pain with the aim of providing pain relief.

Clinical research has shown that, providing you use a good TENS machine, and understand when NOT to use it, significant short-term pain relief can be achieved.

TENS machines are currently medically recommended (depending on your country) for a wide range of painful problems including –

  • Arthritis
  • Back Pain
  • Bruising
  • Calf Strain
  • Dead Leg
  • Fibrositis Joint Pain
  • Headaches Migraines
  • Knee Pain
  • Lumbago Muscle Stress
  • Neck Pain
  • Neuralgia
  • Osteo-arthritis
  • Period Pains
  • Postherpetic Neuralgia
  • Pregnancy/ Labour Pains
  • Rheumatism
  • Sciatica
  • Shoulder Pain
  • Sleeplessness
  • Spondylosis
  • Sports Injuries
  • Tennis Elbow
  • Tenosynovitis
  • Wrist Pain

Image of four TNS machine pads on someone's back

TENS machines are sold on the basis that they provide ‘electrical stimulation to offer short-term pain relief’ – but what does a TENS machine do to reduce pain and what does a good TENS machine do that others don’t?

What Does A TENS Machine Do?

A TENS machine (transcutaneous electrical nerve stimulation) works by you attaching patches (also known as ‘electrodes’) to your body carrying a mild electrical current.

These electrical impulses are designed to work in two ways –

1. To reduce the chance for your CNS (central nervous system) to transmit messages of pain to your brain, by flooding with lots of tiny messages.

2. To stimulate the production of endorphins – groups of hormones that include natural pain relievers.

The electrical current from the TENS machine is designed to stop the nerves sending pain sensation messages through your body to your brain. If the pain messages don’t reach your brain, then they can’t be processed correctly and sent back.

This ‘blocking’ of pain signals is ultimately what helps to relieve pain in the affected area. The whole concept actually relies on what is known the ‘Gate Control Theory’.

We have covered Gate Control Theory and how a TENS machine works in much more ‘How Does A TENS Unit Work?

Many doctors now actively recommend use of a TENS machine as the best form of treatment if rest is unsuccessful, although others may question the lack of clinical evidence behind them.

In certain cases, your doctor’s surgery may already offer training in correct use of the TENS machine, but now these are an established treatment the understanding of how they can help you is much better.

A Dial Scoring Pain Relief From A TENS Machine

About Us

What Are The Benefits of TENS Machines?

Pain Relief

TENS machines are not designed to ‘cure’ the source of your pain, but rather to provide short-term pain relief – sometimes only for as long as they are being used, other times for hours afterwards.

Few Side Effects

They are very safe in as much as there is little that can go wrong (as long as read the instructions). They don’t carry side effects in the way that most modern drugs so and unlike some forms of vigorous exercise, there is little chance of the treatment actually making your pain worse.

Similarly, when they do provide powerful examples of pain relief, it gives you the opportunity to reduce other pain medications that may carry much more dangerous long-term effects.

Easy To Use

They are also non-invasive, while most are fairly small and quite portable. Certain models can even clip to a belt to provide you with pain relief throughout the day and beyond.


Because it is not a chemical designed to affect your mind or chemical balance within your body, TENS machines are considered non-addictive.

Small And Portable

Most TENS machines today are actually small enough to carry around with you. This means you could use them at work, at home – even on the train on your commute to work if you so desired.

Link to the page 'What Does A TENS Machine Do And What Makes A Good One'

Side Effects Of A TENS Machines.

Although I’ve just stated that TENS machines are relatively safe, there are always the odd danger, especially if you don’t read the manual.

The side effects that can happen include an allergic reaction to the electrodes (pads) or an uncomfortableness with the ‘tingling’ feeling of the electrical impulses.

Hypoallergenic patches can be purchased however that should cut out any allergic reaction if you need to.

One other warning though – placing the electrodes on your eyes is not a good idea unless you want an eye injury and similarly putting them on your neck can cause low blood pressure or muscle spasms.

However, as long as you read the guidance and take note of the people who should avoid using a TENS machine you should be fine.

Who Should NOT Use A TENS Machine?

  1. People with a pacemaker or other electrical implant.
  2. People with heart problems
  3. Pregnant women (at least don’t use near the pelvic area and consult you doctor first)
  4. People With Epilepsy. Electrical impulses have been known induce seizures.
  5. If you intend to use a TENS machine on a flight, make sure you get permission from the airline first.

What Does A TENS Machine Do – Using One At Home

As with any form of pain relief, the fact that it works for one person, does mean it will definitely work for someone else.

This is especially true with TENS machines because they can rely on a good understanding of how/ where to apply the TENS machine for various types of pain. We cover exactly what to look for in a good TENS machine further down in this article.

The quality of the TENS machine itself also varies greatly. This is then reflected in their price – typically varying in price for £40 up to £200 depending on various features.

As mentioned some doctor’s surgeries consider them to be essential medical equipment and so have one readily accessible for patients – however depending on the surgery/ your health service or your insurance, each treatment can work out quite costly.

Purchasing a mobile TENS machine of your own has many advantages –

  1. You can use it much more regularly
  2. You can use it when it is most convenient for you.
  3. You can vary the frequency.

This will help with making sure you do not build up a tolerance straight away. As DeSantana et al noted in concluding a clinical trial in 2007 this tolerance can be broken by regularly varying the frequency of the electrical pulses.

Alternatively, and even more effectively – keep the pulses at high intensity (the most efficient level according to the review by Vance et al for ‘Pain Management’ and instead vary the application sites of the electrodes. 

4) You can use it for a variety of pains or keep it just in case you develop new pains later in life. There are a range of studies showing it effectiveness in treating everything from osteoarthritic knee pain (Adedoyin et al) to Fibromyalgia (Lauretti et al)

What Does A TENS Machine Do – What Makes A Good TENS Machine?

As with every item available for purchase, there is a great variety between different makes and models of TENS machines. It is perhaps no great surprise that results vary from person to person, when the unit they use can vary so greatly.

In order to help you, should you decide to invest in a TENS unit in the future, I have listed below what to consider and what to look for when choosing a suitable TENS machine –

1. Number of Outputs/ Channels.

In the case of what a TENS machine can do – the more channels the better. A single output will supply the impulses required for two electrode pads.

Multiple channels however will allow you to use more electrode pads at the same time.

This means you can cover larger areas of your body and save time. It also means you can potentially cover the entire painful area and treat it in one go.

If you have just one sore knee, you may not need this extra coverage, but if it is back pain or even both knees that cause you problems, then having multiple outputs is a real advantage.

2.Intensity Levels.

Again, having more intensity levels typically means you can try different levels of stimulation and decide which achieve better results.

In clinical trials, the machines had two basic levels – low intensity and high intensity. High intensity is intended for acute pain and low frequency is for the more long-term chronic pain.

Throughout the tests, the high intensity levels far outperformed the lower levels (perhaps no surprise there).

However it does allow you to try different ones, reduce the chances of building up a tolerance to it’s effect and find the lowest effective level.

In the same way that a doctor will always try to alter drug doses to find the lowest effective level, you can do exactly the same with an adjustable intensity level.

3. EMS

As mentioned previously when answering the original question ‘what does a TENS machine do?’ the electrical impulses are designed to target the nerves that carry pain. An EMS machine targets muscles instead of nerves, albeit in a similar way.

The aim of an EMS unit is to provide a stimulating massage to your muscles.

The advantage of having a TENS unit that offers both TENS and EMS, is obviously that you can get both a stimulating muscle massage and a nerve blocking pain relief stimulus from the same machine.

4. Specialised Modes.

Modes or programs are either predefined settings for different types of treatment or the option of creating customised programs yourself.

Some models will have what they consider to be the best settings for different parts of your body for either pain relief or massage.

Other models go one step further and offer you the option of selecting different settings and saving them for later use.

Either style gives you an advantage over a standard device – that being the option of trying different types/ styles and comparing which ones are the most effective for you.

5. Battery Life.

Before making a final decision, it is important to consider whether you would benefit more from rechargeable batteries or standard replacement ones. Some machines have built-in rechargeable ones – these are great for cost and can be recharged at any wall outlet or in your car.

The benefit of selecting ones with external batteries (either AA or AAA size) is that you don’t have to keep remembering to recharge your device and the chances of finding it flat again and having to wait for it to charge are nil.

The only thing to be careful of is picking one with 9v batteries – these are still ok, but are harder to find and more expensive than AA or AAA.

6. Size

TENS machines come in all shapes and sizes. If you travel a lot with work or think you might be taking it away from home, then this should be an important consideration.

Many handheld TENS machines are no larger than a smartphone and fit neatly in a hard case, which is ideal for travelling.

Others may be a bit larger and require either their original box or a different box/ backpack for them to fit safely in to.

Some manufacturers also supply special hard plastic cases to protect your TENS machine.

7. Portability

Some TENS units come with belt attachments in their case. This can be really handy if you are looking to use your TENS machine away from home. Especially if you want to use it while travelling as the belt attachment will make this much easier.

8. Timer

Most units come with some form of timer, which can be essential. In the new units, it is included for safety reasons (some will have an automatic switch off), but is also great for measuring effectiveness.

You can try different lengths of use to see at which point you stop seeing any further benefit. Using a TENS machine for too long can cause bruising, although this is very unlikely unless it is your first ever session.

9. Screen Size

Whether you are looking to use you TENS machine at home or at work (or anywhere else for that matter), having a screen that you can actually see and comfortably use, will make a lot of difference.

A good screen should be big enough to see and use with ease, allowing you to change the settings quickly without complication. It is also a real advantage if it is a backlit one as this will help with use in all situations.

Although screen size is listed at number 9 it is perhaps one of the most important factors, especially when it comes to usability.

10. Pad Size

Image of a TENS Machine Pad attached to someone's back

Electrode pads can vary greatly in size. Large pads are ideal for non-specific back pain or covering large areas.

Medium pads are a safe compromise and the most common to be supplied with your TENS machine.

Small pads are perfect for treating muscle knots (under an EMS setting) or joint pain. They are ideal for treating small, sometimes confined, areas.

11. Replacement Pads

If you use your TENS machine for any period of time, you will need to replace the pads from time to time. Most models will only work with dedicated pads from the same manufacturer.

However, there are some generic pads that will work with most machines if you find that you don’t like the supplied pads, for whatever reason.

12. Ease Of Use

To put it simply – if you select a good machine, with all the features above that suit your requirements (good screen size, large pads, a belt clip, a timer, an easy set intensity changes, a good selection of channels to try and the option of EMS…. And you will have a brilliant machine that already is easy to use.

Conclusion –

So…what does a TENS machine do? Well, with the use of clever electrical pulses it can block the pain signals travelling to your brain.

This can provide essential pain relief for many people.

Of course, there is no guarantee that a TENS machine will work for everyone, but then no pain treatment does.

Perhaps the biggest vote for their effectiveness, and there is data that backs up their use as well, is that many family doctors now see them as a viable alternative to painkillers, without all the side effects.

If you do decide that a TENS machine could help you, just make sure you read the guidance on what to look for in a good one above.

I have been asked numerous times over the past few years to help with choosing a device and so have always kept abreast of the latest changes in the market.

I will soon be releasing a list with my recommendation on soon, while I check out this years’ releases and compare to my original favourite, so check back soon (March 2020) if you need further guidance.

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References –

1. DeSantana JM, Santana-Filho VJ, Sluka KA. (2007) Modulation between high- and low-frequency transcutaneous electric nerve stimulation delays the development of analgesic tolerance in arthritic rats. Archives Of Physical Medicine And Rehabilitation.

2. Carol GT Vance, Dana L Dailey , Barbara A Rakel & Kathleen A Sluka. (2014). Using TENS for pain control: the state of the evidence. Pain Management

3. Adedoyin RA, Olaogun MO, Fagbeja OO. (2002) Effect of interferential current stimulation in management of osteo-arthritic knee pain. Physiotherapy 88, 493–499 (2002).

4. Lauretti GR, Chubaci EF, Mattos AL. (2013). Efficacy of the use of two simultaneously TENS devices for fibromyalgia pain. Rheumatol. Int. 33, 2117–2122 (2013)

Do You Have A Question (Clinical Or General)? Please Leave It Below And We’ll Be Sure To Respond…..

This Post Has 6 Comments

  1. Jay Silk

    Where can I buy a Tens Machine and how much do they cost.

  2. Jay Silk

    Where can I buy a Tens Machine

    1. HRPAdmin

      Hi Jay, you can buy a TENS machine in many different places – amazon are probably as good as anywhere. I am just in the process of putting a review panel of members that have TENS machines so we can review a good portion of the market. I’ll let you know as soon as this is ready. Thanks for reading!

  3. Valery Wakenight

    Thank you for this detailed info what does a tens machine do? I think I will need to try one for my lower back pain. Thanks again. Would like to know best ones tho if poss?

  4. Jacky Clarke

    Hi Michael, Thanks for this. I am considering purchasing a TENS machine and was wondering if you could tell me what to look for when buying one? Many thanks!

    1. HRPAdmin

      Hi Jackie, No problem – I’ve sent you an e-mail. Now I’ve got a few members that own TENS machines, I will ask them to tell to help with a review panel and will put up a list for different needs/ budgets sometime in early 2020. Kind regards, Michael

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