Design: Cross-sectional study.
Setting: Neurophysiology research laboratory at the Anglo-European College of Chiropractic.
Subjects: Twelve participants with 24 upper trapezius muscles.
Methods: Surface electromyography (EMA) was applied to 24 upper trapezius muscles, containing either latent or active trigger points, using 3 disposable pre-gelled electrodes placed on each shoulder parallel to the direction of the muscle fibres. After a 1-min baseline-recording period, participants were instructed to perform a sequence of three maximal shoulder shrugs with each held for 3 s. This was then followed by a 3-min period of relaxed sitting. A myofascial pain medicine clinician identified the muscles containing active and latent trigger points. The neurophysiologist conducting the electromyography and data analysis was masked to the identity of the muscles containing the type of trigger point until after data analysis.
Results: Of the 24 upper trapezius muscles examined 33% had active trigger points while 67% contained latent trigger points. The root mean square (RMS) EMG amplitude was normalised to the mean value for the three shrugs, and the data grouped according to the presence of active or latent trigger points. In all cases, activity in the muscles containing active trigger points was less than that in the muscles with latent trigger points; however, in no case did this reach statistical significance.
Conclusion: The results suggest that there is a trend for muscles containing active trigger points to have less electrical activity than muscles containing latent trigger points; however, further research is necessary before it can be determined if surface electromyography is able to differentiate activity in upper trapezius muscles with latent trigger points from those with active trigger points.
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