Transcutaneous Electrical Nerve Stimulation (TENS) Explained Simply

1. What It Is About

TENS stands for transcutaneous electrical nerve stimulation. This means electrical impulses pass through the skin, i.e. transcutaneously, and reach the nerves. Two electrodes are attached to the skin for this purpose, for example next to a surgical wound or on a painful area. A small portable device generates the impulses.

The idea behind this is that pain signals travel to the brain via the spinal cord. Other nerve fibres can send signals there that weaken these pain signals. This process is called gate control. The electrical impulses are intended to 'close' this gate, so to speak. TENS has been studied since the 1970s; it was first used in rehabilitation, later for chronic pain, after surgery and in neurological conditions.

The devices offer many settings: how quickly the impulses come, how strong the current is and where the electrodes are placed. In studies, individual sessions usually lasted between 20 and 60 minutes, often several times a day. For research, this is a challenge, as two studies with different settings are difficult to compare.

2. What Studies Show

TENS is best studied after surgery. A review of several studies from 2003 compared studies in which TENS was properly adjusted with those in which the setting was too weak 1. Proper adjustment meant the electrodes were placed in the area of the surgical wound and the current was strong but not painful. In these studies, pain decreased significantly more, and less pain medication was required. When the current was too weak, almost no difference was seen. The setting therefore appears to be crucial.

A randomised study, in which participants were randomly assigned to different treatments, examined 50 patients after thoracic surgery (thoracotomy). For five days, TENS was compared with a sham treatment without current 11. With TENS, pain levels were lower, less pain medication was used, and lung function was better. Certain immune system messenger substances in the blood also changed. Whether this change in the blood has any meaning for how a person feels or recovers is not yet clear.

In fibromyalgia, a condition characterised by widespread pain and fatigue, TENS showed an effect in two studies. A 2013 study observed that pain during movement decreased and fatigue improved 2. A controlled study from 2020 also found less pain during movement and less fatigue; the effect lasted for four weeks 8. In osteoarthritis of the knee, high-frequency TENS increased the pain threshold in one study, while low-frequency TENS showed no clear effects 5. After a hip fracture, participants using TENS walked further in a walking test and required less pain medication 10.

Regarding tolerability: in the studies, fewer than 5 out of 100 participants experienced an adverse effect, usually mild skin irritation or muscle twitching 3. No serious adverse events were reported.

3. What Remains Unclear

A Cochrane review from 2019, which summarised several reviews on chronic pain, found no consistent evidence that TENS is more effective than a sham treatment 7. Sham treatments are difficult: if participants feel the current, they often know whether it is active treatment. This can bias the results.

There is some evidence of an effect in nerve pain and spasticity after a stroke, but the studies are small and vary in design 6, 9. It also remains unclear how long an effect lasts: most studies looked at less than six weeks. Which setting works best for which type of pain is also not clear.

4. What This Means in Everyday Practice

For an assessment, this means: TENS is a well-tolerated procedure, and there are areas in which studies have shown it can improve pain, fatigue and pain medication use — especially after surgery, in fibromyalgia and in joint wear. A striking finding is that the results depend heavily on how the device is set up. Studies with only weak current showed almost no effect.

Less clear is how much of the effect comes from participants' expectations. In pain studies, this is generally difficult to separate. The next task for research is a comparison of different settings for the same type of pain over a longer period. This would show which application has been tested for which condition. It is also unclear what role electrode placement plays.

All details with study numbers and sources: detailed page on Transcutaneous Electrical Nerve Stimulation (TENS). For children: Transcutaneous Electrical Nerve Stimulation (TENS) for children.