Do F-wave measurements detect changes in motor neuron excitability?
The use of F waves to assess motor neuron excitability in experimental paradigms has never been validated. Our objective was to determine whether F-wave area, amplitude, and persistence measurements change in response to manipulations known to alter the excitability of motor neurons. The effects of muscle vibration, contraction of a remote muscle, and high-intensity stimulation of ipsilateral or contralateral fingers were assessed in 12 healthy volunteers. F-wave area, amplitude, and persistence all declined with ipsilateral cutaneous stimulation. The other maneuvers facilitated some, but not all, of the F-wave measurements. Changes in F-wave area and amplitude were correlated, but neither correlated with changes in persistence. A sample size of 50-75 F waves was needed to approximate amplitude and area results from 100 F waves with an accuracy of +/- 25%. We conclude that changes in F waves are better at detecting inhibition than facilitation of motor neurons. F waves reflect motor neuron excitability in a general way but do not allow for accurate measures of short-term changes in excitability.
Electromyography Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bldg. 10, Room 5C101, 10 Center Drive MSC 1404, Bethesda, Maryland 20892-1404, USA.
Jenny Z
JZ
Lin
Mary Kay
MK
Floeter
D000200:Action Potentials / Q000502:physiology*; D000328:Adult; D000704:Analysis of Variance; D004558:Electric Stimulation / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D014732:Vibration