Generation of Repeater F Waves in Healthy Subjects.

PURPOSE

F waves identical in latency, size, and shape, known as repeater F waves, have been observed occasionally in normal motor conduction recordings. The purpose of this study was to examine the occurrence and characteristics of repeater F waves in healthy subjects under different testing conditions, aiming to selectively excite lower and higher threshold motor fibers.

METHODS

Sessions of 40 traces were recorded from the ulnar nerve in 12 volunteers, applying/using supramaximal, submaximal stimuli (intensity able to elicit 30% and 60% of the maximum compound muscle action potential amplitude), and a collision technique. Repeater F waves were identified and their numbers and relative frequency were estimated. For this purpose, a custom-designed software program was developed, to avoid misjudgments of simple visual inspection.

RESULTS

Repeater occurrence was significantly higher using 30% submaximal intensity compared with the standard supramaximal stimulation. There was an inverse significant association between repeater index and overall F wave quantity. Repeaters' latency, amplitude, and duration measurements were within the ranges of the nonrepeaters.

CONCLUSIONS

We herein showed that in healthy subjects the presence of repeater F waves might increase, when stimulation conditions other than standard single, supramaximal impulses were used. The frequency of repeaters was dependent on the overall F wave persistence, but there was no evidence to support a relationship with the type of motoneurons that was preferentially stimulated.