The Effect of Frequency Modulation in TENS on Habituation and Pain Threshold
Condition: Transcutaneous Electrical Nerve Stimulation
Study type: Interventional

Summary: 
      Purpose

      The purpose of this study is to determine whether application of Transcutaneous Electrical
      Nerve Stimulation (TENS) is effective on habituation to electrical current whether delivered
      at a fixed frequency of 100 Hz or at patterned frequency. The secondary purposes are to
      determine the effectiveness on mechanical pressure pain and the subjective perception of the
      subjects regarding habituation and comfort of the different stimulations.
    

Detailed description: 
      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.
    

Intervention name(s): TENS: Randomized frequency modulation; TENS: Scan 6/6 of frequency modulation; TENS: Fixed frequency; Sham Stimulation
Intervention type(s): Device; Device; Device; Device
Intervention description(s): Transcutaneous application of Conventional TENS current over the course of the superficial radial nerve in the right forearm for a 20 minutes session. The intensity of the current will increase until participants report a "strong but comfortable" sensation, just Transcutaneous application of Conventional TENS current over the course of the superficial radial nerve in the right forearm for a 20 minutes session. The intensity of the current will increase until participants report a "strong but comfortable" sensation, just below motor threshold. Currents parameters are:
Frequency modulation: randomized pattern (from 80 to 120 Hz) Pulse width 200 microseconds; Transcutaneous application of Conventional TENS current over the course of the superficial radial nerve in the right forearm for a 20 minutes session. The intensity of the current will increase until participants report a "strong but comfortable" sensation, just below motor threshold. Currents parameters are:
Frequency modulation: Scan of frequency from 80 to 120 Hz in 6/6 mode (frequency sweep from 80 Hz to 120 Hz in 6 seconds and from 120 to 80 Hz in 6 secons) Pulse width 200 microseconds; Transcutaneous application of Conventional TENS current over the course of the superficial radial nerve in the right forearm for a 20 minutes session. The intensity of the current will increase until participants report a "strong but comfortable" sensation, just below motor threshold. Currents parameters are:
Fixed frequency at 100 Hz Pulse width 200 microseconds; Electrodes are placed over the course of the superficial radial nerve in the right forearm for a 20 minutes in the same manner as experimental groups, but will be applied a sham electrical stimulation increasing the current intensity of an unconnected channel.
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Double (Participant, Outcomes Assessor)
Primary purpose: Treatment
Keywords: Pain Threshold; Transcutaneous Electrical Nerve Stimulation; Habituation