TENS explained: how transcutaneous electrical nerve stimulation works

A TENS machine works by sending mild electrical impulses through adhesive electrodes stuck to your skin. These impulses stimulate nerves and can dampen the transmission of pain signals in the spinal cord. TENS stands for transcutaneous electrical nerve stimulation. It is a drug-free method that has been used in medicine and physiotherapy for decades.

Contents

• What is a TENS machine?
• How exactly does TENS work?
• What is the gate control theory?
• How do you use a TENS machine?
• What is TENS used for?
• Is TENS safe? Side effects and contraindications
• Common questions about TENS

What is a TENS machine?

TENS is short for transcutaneous electrical nerve stimulation. Roughly translated, that means: electrical stimulation of nerves through the skin. A TENS machine is a small, usually battery-powered device connected to adhesive electrodes by cable or directly.

The electrodes stick to the skin. Through them the device delivers weak electrical impulses. Frequency and strength can usually be adjusted. Many people describe the sensation as a light tingling, prickling or tapping.

The method has been used in pain medicine and physiotherapy since the 1970s. It belongs to the so-called physical methods, so it works with a physical stimulus instead of medication.

How exactly does TENS work?

The electrical impulses from a TENS machine stimulate the nerve fibres under the skin. That sets two mechanisms in motion, and they work together.

First, the stimulus influences how pain signals are passed on in the spinal cord. Put simply, the stimulation can weaken the transmission of pain signals to the brain. The technical term for this is the gate control theory, more on that in a moment.

Second, the stimulation can prompt the body to release its own pain-inhibiting messengers, such as endorphins. These natural substances have a similarly calming effect on how you perceive pain.

Which mechanism dominates depends partly on the frequency you set. Higher frequencies aim more at the gate control effect, lower ones more at the release of endorphins. That is exactly why many devices let you adjust frequency and intensity.

What is the gate control theory?

The gate control theory is the best-known model for explaining how TENS works. It was presented in 1965 by the researchers Ronald Melzack and Patrick Wall.

The idea can be described with a gate. In the spinal cord there is a kind of checkpoint that pain signals have to pass through on their way to the brain. This gate can be open or closed.

If TENS now stimulates other nerve fibres, their signals compete with the pain signals for passage. Put simply: the extra stimulus can partly close the gate, so less pain signal reaches the brain. It is also the reason we instinctively rub a sore spot. There too we overlay the pain signal with another stimulus.

One thing matters here: the theory describes a mechanism by which stimulation can work. How strong the effect is in any individual case depends on many factors and differs from person to person.

How do you use a TENS machine?

The basic principle is simple, but it is worth being careful. This is how it usually goes:

• Place the electrodes. The adhesive electrodes go on clean, intact skin near the painful area. The exact position affects the result.
• Choose a programme and strength. Most devices let you set frequency and intensity. Start low and increase slowly until you feel a clear but comfortable tingling.
• Watch the duration. Depending on the recommendation, a session often lasts between 20 and 45 minutes and can be repeated several times a day.
• Check your skin. Look at the skin after each session. Redness where the electrodes sat is possible and normally fades again.

At the start especially, it helps to have a doctor or physiotherapist show you how to handle the device. They can help with the right electrode placement and suitable settings.

What is TENS used for?

TENS is used in medicine and physiotherapy for very different kinds of pain, both acute and longer-lasting. Common areas are back pain, neck pain, joint complaints or pain after injuries.

TENS has also been studied for period pain. There is a Cochrane review on this question that pools several randomised trials. All in all, TENS is one of the recognised drug-free methods that can have a place in pain treatment.

How well TENS works varies from person to person. For some the effect is clear, for others barely noticeable. TENS does not replace a medical work-up of what is causing your pain. It is a possible addition, not a substitute for a diagnosis.

Is TENS safe? Side effects and contraindications

Used correctly, TENS is considered well tolerated. The most common side effect is skin irritation or redness under the electrodes. Still, there are clear situations in which TENS should not be used, or only after talking to a doctor.

Important contraindications include:

• A pacemaker or other active implants
• Pregnancy, especially on the abdomen and pelvis
• Acute inflammation, open wounds or skin conditions in the treatment area
• Epilepsy
• Altered sensation or absent pain perception in the treated region
• Thrombosis or marked vein disease at the application site

The electrodes should also not be placed on the neck, over the heart or on irritated skin. If you have a pre-existing condition, feel unsure or want your symptoms checked, raise it with your doctor or physiotherapist beforehand. This list does not replace individual advice.

This article is for general information and does not replace medical advice. If your symptoms are severe, unusual or persistent, please see your gynaecologist.