Does the pulse frequency of transcutaneous electrical nerve stimulation (TENS) influence hypoalgesia?: A systematic review of studies using experimental pain and healthy human participants

ObjectivesTo determine the hypoalgesic effect of pulse frequency of transcutaneous electrical nerve stimulation (TENS) when all other TENS parameters are held constant.Data sourcesSystematic review of studies using experimentally induced pain on healthy participants where there was a head-to-head comparison of different pulse frequencies. AMED, CINAHL, EMBASE, Inspec, PEDro, Pre-CINAHL, PsycARTICLES, PubMed, SPORTDiscus were searched in September 2006.Review methodsInclusion criteria were studies that directly compared two or more pulse frequencies head-to-head and recorded outcome as change in pain threshold or pain intensity. Studies were excluded if pulse intensity, pulse pattern, or pulse duration of TENS were not standardized between groups. Two reviewers judged the trial outcome independently. Primary outcome was a report of a statistically significant difference between pulse frequencies for pain threshold or intensity at any time point through the experiment.ResultsTwenty studies were identified, of which 13 experimental studies from 12 published reports were included for review. Ten studies found no statistically significant differences in hypoalgesia between pulse frequencies. Of the three studies judged as positive outcome, one reported that 100 pulses per second (pps) was superior to 10 pps; one that 4 pps was superior to 100 pps; and one that 5 pps and 80 pps were superior to 2 pps.ConclusionEvidence from experimental pain studies suggests that TENS pulse frequency does not influence hypolagesia when its pulse intensity, pulse pattern, and pulse duration are kept constant. Inadequate sample sizes may have generated false negative findings in some studies.