title: Standardization of facilitation of compound muscle action potentials using a modified myometer during magnetic stimulation in healthy volunteers.
abstract: In 20 normal subjects motor evoked potentials (MEPs) from first dorsal interosseous (FDI) were obtained following transcranial magnetic stimulation during relaxation and voluntary contraction of 2-20% of maximum. A new method to standardize facilitation of MEP using surface EMG and a modified myometer was used. The MEP amplitudes increased significantly at contraction levels of 2%, 10% and 15% of maximum. The latencies decreased significantly at contraction levels of 2%, 5% and 15%. Coefficients of variation of the amplitude decreased from 6.4% during relaxation to approximately 2% during facilitation. In contrast, coefficients of variation of take-off latencies (T-lat) increased significantly from 1.7% during relaxation to approximately 3% during facilitation. The variability of amplitudes and latencies was mainly due to inter-individual variation. The observations in the present study indicate that the actual contraction level should be precisely defined during transcranial magnetic stimulation.
authors.affiliation: Department of Neurology, Arhus University Hospital, Denmark.
authors.forename: J F
authors.initials: JF
authors.lastname: Nielsen
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000328:Adult; D004576:Electromyography; D005260:Female; D006801:Humans; D008280:Magnetics; D008297:Male; D008875:Middle Aged; D009132:Muscles / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D012015:Reference Standards; D012016:Reference Values