Quantitative surface EMG of pericranial muscles. Relation to age and sex in a general population

Quantitative EMG levels in pericranial muscles were studied in 547 subjects randomly selected from the general population aged 25-64 years. Surface EMGs of the right frontal and both temporal muscles were examined during rest and maximal voluntary contraction by a blind, standardized method. The amplitude of the EMG was expressed as the root mean square and mean rectified voltage. The power spectrum was calculated and the mean and median frequencies were extracted. During rest no significant differences were found between amplitude levels of the temporal muscles, while higher frequency levels were detected on the left side. Amplitude and frequency levels were higher in the frontal than the temporal muscles during rest, but lower during maximal voluntary contraction, probably for morphological differences. In the frontal muscle, females had increased amplitudes during rest and decreased levels during maximal voluntary contraction compared to males, indicating a higher tension at rest and a reduced number and/or size of muscle fibers in females. During maximal voluntary contraction a highly significant decrease with age was seen in amplitude and frequency in the temporal muscles. The present study is the first population study of EMG levels in pericranial muscles and constitutes the necessary basis for evaluating the EMG in tension-type headache.