Alteration of interferential current and transcutaneous electrical nerve stimulation frequency: effects on nerve excitation.

OBJECTIVES: To investigate the effects of different interferential current (IC) and transcutaneous electrical nerve stimulation (TENS) frequencies on sensory, motor, and pain thresholds. STUDY DESIGN: Single blind, repeated measures design. SETTING: Laboratory. PARTICIPANTS: Women students 18 to 30 years old (n = 24). INTERVENTIONS: Premodulated IC and square-wave TENS pulses (125micros phase duration) were applied over the median nerve at a range of frequencies in all subjects. MAIN OUTCOME MEASURES: The peak current (in milliamperes) was recorded twice at each threshold for each frequency, and averaged. RESULTS: Both IC and TENS displayed a statistically significant effect of frequency for each threshold. However, frequency effects with IC were not well defined and were of small magnitude. Pure 4kHz current (0Hz amplitude modulated frequency) with IC did not produce effects different from those produced when an amplitude modulated frequency was included. With TENS, frequency effects were very clearly observed, with a distinct increase in the current intensity at each threshold as frequency decreased. CONCLUSIONS: It is postulated that the medium frequency component of IC is the main parameter in stimulation, contrary to traditional claims of the amplitude modulated frequency being important. TENS was shown to be a more adaptable method of stimulating these nerve pathways than IC.