title: Characteristics of electrical activity in trapezius muscles with myofascial pain.
abstract: OBJECTIVE
  To study the reliability and validity of resting electrical activity from tender areas in muscle.
  
  
  METHODS
  In seven subjects with tender areas in their trapezius muscles, electromyographic (EMG) signals were obtained from monopolar needles at various depths over the tender area and at the same depths over the control area, and from surface electrodes. At selected depths, multiple epochs were recorded.
  
  
  RESULTS
  Increased electrical activity occurred from the electrode inserted toward the tender area in all seven subjects (to a mean of 47.6 microV), but not from control areas. The depths of the maximal EMG amplitudes advancing and withdrawing the needle were usually within 3 mm. The EMG amplitude from the first of multiple epochs (38.4 microV) did not differ from the average (40.0 microV) of subsequent epochs (paired-t test, 6 df, 0.2<p<0.3).
  
  
  CONCLUSIONS
  We suggest that the electrical activity arises from a localized zone and is stable over time.
  
  
  CONCLUSIONS
  Our data provide evidence for the reliability and validity of the electrical activity from myofascial tender areas.
authors.affiliation: Department of Oral Medicine and Oral Diagnosis, School of Dentistry and Dental Research Institute, Seoul National University, Seoul, South Korea.
authors.forename: Jin Woo
authors.initials: JW
authors.lastname: Chung
authors.forename: Richard
authors.initials: R
authors.lastname: Ohrbach
authors.forename: W D
authors.initials: WD
authors.lastname: McCall
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000328:Adult; D004566:Electrodes; D004576:Electromyography; D004594:Electrophysiology; D005260:Female; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000503:physiopathology*; D009209:Myofascial Pain Syndromes / Q000503:physiopathology*; D010147:Pain Measurement; D017288:Pain Threshold / Q000502:physiology; D010173:Palpation; D015203:Reproducibility of Results