Quantitative surface EMG of pericranial muscles. Reproducibility and variability.

We present reproducibility data on a quantitative electromyographic investigation of the temporal and frontal muscles using surface electrodes. Such data have not been published before. They constitute a necessary basis for future evaluation of the importance of pericranial muscles in tension-type headache. Root mean squares and mean rectified values of the electrical activity were measured in 20 healthy subjects. Power spectra were calculated and the mean and median frequencies were extracted. The coefficient of intraindividual variation in RMS from the right temporal muscle within the same examination was 14%, between several examinations on the same day 18% and between measurements on 2 different days 18%. The corresponding coefficients of interindividual variation were 36, 31 and 38%. The left temporal and frontal muscles showed similar coefficients of variation. At rest, no differences were found between muscles, but during maximal voluntary contraction the frontal muscle revealed a 55% lower RMS values than the temporal muscles. The method used was reproducible and reliable in measuring quantitative electrical activity of pericranial muscles.