Optimal frequencies for electric stimulation using medium-frequency alternating current.
OBJECTIVE
To determine the effect of single cycles of alternating current of various frequencies on sensory and motor thresholds and on relative thresholds (motor threshold/sensory threshold).


METHODS
Repeated-measures design.


METHODS
Laboratory setting.


METHODS
University student and staff volunteers (N=16; mean age, 34y).


METHODS
Single cycles of sinewave frequencies between 1 and 35kHz were delivered at 50Hz. The frequencies were applied in a random order.


METHODS
The motor and sensory thresholds were recorded at each applied frequency.


RESULTS
Both sensory and motor thresholds showed a smooth decrease to a minimum at approximately 3kHz. The relative threshold reached a minimum close to 9kHz. Comparison with previous studies showed that although absolute thresholds reach a minimum at a frequency that depends on electrode size, the frequency at which the relative threshold is a minimum was independent of electrode size and independent of whether the stimulus was applied as single pulses or in burst mode.


CONCLUSIONS
The optimal frequency for transcutaneous stimulation using medium-frequency alternating current depends on the outcome measure used. It would therefore be desirable for clinical stimulators to provide a selection of carrier frequencies.
Ward
Alex R
AR
Department of Human Physiology and Anatomy, La Trobe University, Victoria, Australia. a.ward@latrobe.edu.au
Robertson
Valma J
VJ
Makowski
Raphael J
RJ
D000328:Adult; D004558:Electric Stimulation / Q000295:instrumentation / Q000379:methods*; D004566:Electrodes; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology; D017288:Pain Threshold / Q000502:physiology*; D012016:Reference Values; D012044:Regression Analysis; D012684:Sensory Thresholds / Q000502:physiology*