The Effect of Frequency Modulation in TENS on Habituation and Pain Threshold

Low frequency and low intensity TENS showed strong evidence of inefficiency while conventional high frequency TENS (around 100Hz) applied at "strong but comfortable" intensity proved strong evidence of efficacy on pressure pain. In addition, some studies have shown the importance of current intensity in the effect of TENS. Either in clinical practice and in research, TENS intensity is usually adjusted according to the sensation of the subjects "strong but comfortable" "strong just below the motor threshold", ...). Usually throughout the TENS applications there is a phenomenon called "habituation" that involve a wide decrease of the sensation of the current applied, even though the perception the output-parameters are maintained. In this sense, It has been seem that adjusting the intensity throughout the TENS intervention produced a greater hypoalgesic effect than when the intensity remained fixed. On the other hand, most TENS devices offer the possibility of modulating current with the aim of preventing habituation phenomenon. The modulation of the electric current consists of changing the characteristics of the current (pulse width, pulse frequency, ...) every few seconds during the intervention. Nevertheless, the most common pattern used is the frequency modulation. However, there is a lack of evidence regarding what it is the better methods to avoid habituation during a TENS application.