An investigation into the analgesic effects of different frequencies of the amplitude-modulated wave of interferential current therapy on cold-induced pain in normal subjects.

OBJECTIVE

To investigate the analgesic effects of different amplitude-modulated frequencies of interferential current therapy (IFT) on cold-induced pain in healthy subjects.

DESIGN

Single-blind parallel group methodology was used. Subjects completed 6 cycles of the cold-induced pain test (2 pretreatment, 2 during treatment, 2 posttreatment). During each cycle, subjects plunged their hand into iced water and the time taken to reach pain threshold was recorded. The hand remained immersed in the iced water for a further 30 seconds, after which the self-reports of pain intensity and pain unpleasantness were recorded.

SETTING

Laboratory in the United Kingdom.

PARTICIPANTS

Sixty unpaid, pain-free volunteers without a known pathology that could cause pain.

INTERVENTIONS

IFT delivered on the nondominant arm at a "strong but comfortable" intensity without visible muscle twitches, using a quadripolar application technique at 1 of 6 possible amplitude modulated "beat" frequencies (20, 60, 100, 140, 180, 220Hz).

MAIN OUTCOME MEASURES

The percentage change in pain threshold, pain intensity, and pain unpleasantness from the pretreatment baseline.

RESULTS

Two-way repeated-measures analyses of variance found no effects for groups for pain threshold (P=.11) or pain ratings (P>.05). There were no effects for cycle for any of the outcome measures. Effects for group by cycle interaction were noted for pain intensity and unpleasantness ratings (P<.05), although post hoc analysis failed to determine the nature of this interaction.

CONCLUSIONS

Experimentally induced cold pain was not influenced by IFT frequencies.