Lowering of Sensory, Motor, and Pain-Tolerance Thresholds With Burst Duration Using Kilohertz-Frequency Alternating Current Electric Stimulation: Part II
Abstract
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.
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 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 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 (∼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.
Conclusions
Our 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.
Musculoskeletal Research Centre, Faculty of Health Sciences, La Trobe University, Victoria, Australia
Reprint requests to Alex R. Ward, PhD, School of Human Biosciences, Faculty of Health Sciences, La Trobe University, Victoria, 3086, Australia
Supported by ongoing research grants from the Faculty of Health Sciences, La Trobe University (grant no. FRG6/A12) and the School of Human Biosciences, La Trobe University (grant no. 100226).
No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the authors or on any organization with which the authors are associated.
ABSTRACT