Does amplitude-modulated frequency have a role in the hypoalgesic response of interferential current on pressure pain sensitivity in healthy subjects? A randomised crossover study.

OBJECTIVE

To investigate the hypoalgesic effect of amplitude-modulated frequency during interferential current therapy using an experimentally induced mechanical pain model in normal subjects. This study examined pain pressure sensitivities achieved when the amplitude-modulated frequency parameter was present (100Hz) and absent (0Hz).

DESIGN

Randomised controlled crossover trial with repeated measures.

SETTING

University research laboratory.

PARTICIPANTS

Forty-six healthy volunteers (23 males, 23 females).

INTERVENTIONS

Two interferential therapy protocols (with and without amplitude-modulated frequencies) were applied to the lumbar area on two different days.

MAIN OUTCOME MEASURES

Pressure pain thresholds over the lumbar area were measured before, during and after application of the interferential therapy protocols.

RESULTS

A three-way analysis of variance with repeated measures failed to show any statistically significant difference between the two protocols in modifying pressure pain threshold values (mean difference 0.017kg/cm(2), 95% confidence interval -0.384 to 0.350, P=0.93). Statistically significant differences were identified (P<0.001) between measurements, indicating a comparable decrease in pain sensitivity in both groups. However, the increase in pressure pain thresholds (0.76kg/cm(2)) failed to reach a level of clinical importance.

CONCLUSIONS

The addition of an amplitude-modulated frequency parameter to interferential therapy did not influence mechanical pain sensitivity in healthy subjects. Amplitude-modulated frequency is therefore unlikely to have a physiological hypoalgesic effect.