Lowering of Sensory, Motor, and Pain-Tolerance Thresholds With Burst Duration Using Kilohertz-Frequency Alternating Current Electric Stimulation: Part II

Ward AR, Lee Hung Chuen WL. Lowering of sensory, motor, and pain-tolerance thresholds with burst duration using kilohertz-frequency alternating current electric stimulation: part II.ObjectiveTo determine the optimum burst duration for discrimination between sensory, motor, and pain tolerance thresholds using 20-Hz bursts of kilohertz-frequency sinusoidal alternating current (AC) applied transcutaneously to human participants.DesignA within-subject, repeated-measures trial.SettingA research laboratory.ParticipantsHealthy young adults (N=20).InterventionsBursts of AC electric stimulation at frequencies of 1 and 4kHz. The burst frequency was 20Hz. Burst durations ranged from 250 microseconds (for 1 cycle of 4-kHz AC) and 1 millisecond (for 1 cycle of 1-kHz AC) to 50 milliseconds (continuous AC).Main Outcome MeasuresMeasurement of sensory, motor, and pain-tolerance thresholds.ResultsThresholds decreased to a minimum with increasing burst duration. The minimum threshold identified the utilization time over which summation of subthreshold stimuli occurs. Utilization times were different for sensory (∼20ms), motor (∼30ms), and pain (>50ms) and were much higher than found in a previous study that used a higher burst frequency (50Hz). As with the previous study, relative thresholds were found to vary with burst duration. Despite the very different utilization times, maximum separation between sensory, motor, and pain thresholds was found to occur with bursts in the range of 1 to 4 milliseconds, the same range found in the previous study.ConclusionsOur conclusions concur with those reported previously and support the contention that short-duration kilohertz-frequency AC bursts (1–4ms) have a more useful role in rehabilitation than the long-duration kilohertz-frequency bursts that characterize Russian and interferential currents.