When the TENS machine is turned on, it sends small electrical impulses to the affected area of the body, which can be felt as a tingling sensation. These electrical impulses can reduce pain signals that reach the spinal cord and brain, providing relief from pain and relaxation of muscles. People can carry a TENS unit in their pocket or clip it to a belt for easy access to pain relief throughout the day. A recent randomized controlled trial found that TENS applied to people with knee arthrosis as a complementary treatment to primary care showed no additional benefit.
However, one study found that TENS treatment provided temporary pain relief to people with fibromyalgia while the machine was in use. Both high-frequency (HF) and low-frequency (LF) TENS have been shown to provide analgesics when applied at a strong and painless intensity, and HF TENS may be more effective for people taking opioids. Animal studies suggest that tolerance to TENS may be delayed by pharmacological methods, as well as by non-pharmacological modulation of TENS parameters. The activation of inhibitory pathways by TENS is thought to reduce excitation and subsequent neuronal sensitization in the spinal cord, leading to analgesic effects.
However, there is a lack of randomized trials on TENS compared to conventional therapy, making it difficult to evaluate its effectiveness. Factors that affect the effectiveness of TENS include the population and outcome evaluated, timing of outcome measures, negative interaction of opioid use, and parameters of the TENS dose. In order for TENS to be most effective, experts recommend applying it at the highest intensity that can be tolerated. Applying TENS electrodes to acupuncture points can increase analgesics, and focusing on using TENS during movement or required activity may provide the greatest benefit.