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Published on: April 5, 2019
Lowering of sensory, motor, and pain-tolerance thresholds with burst duration using kilohertz-frequency alternating
Alex R Ward1, Wendy Lee Hung Chuen
1Musculoskeletal Research Centre, Faculty of Health Sciences, La Trobe University, Victoria, Australia. a.ward@latrobe.edu.au
Objective:
To 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.
Design:
A within-subject, repeated-measures trial.
Setting:
A research laboratory.
Participants:
Healthy young adults (N=20).
Interventions:
Bursts of AC electric stimulation at frequencies of 1 and 4 kHz. The burst frequency was 20 Hz. 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 Measures:
Measurement of sensory, motor, and pain-tolerance thresholds.
Results:
Thresholds 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 (approximately 20 ms), motor (approximately 30 ms), and pain (>50 ms) and were much higher than found in a previous study that used a higher burst frequency (50 Hz). 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.
Conclusions:
Our conclusions concur with those reported previously and support the contention that short-duration kilohertz-frequency AC bursts (1-4 ms) have a more useful role in rehabilitation than the long-duration kilohertz-frequency bursts that characterize Russian and interferential currents.
