Spontaneous needle electromyographic activity in myofascial trigger pointsin the infraspinatus muscle: A blinded assessment

Objective: Myofascial pain syndromes associated with trigger points [TrPs] are an established clinical entity but the structural and functional abnorm alities of TrPs are not well understood. The aim of the study was to conduc t a blinded electromyographic investigation of TrPs. Methods: Nineteen young subjects with chronic shoulder and arm pain, who ha d a TrP [i.e., a tender point with referred pain, producing at least some o f the pain complaint] in the infraspinatus muscle, were examined. This poin t and a nontender control point in the same muscle were code-marked, in ord er to blind the examiner. Around both points 20 concentric needle electromy ographic [EMG] recordings were obtained at rest. Results: More subjects had spontaneous EMG activity at the TrPs than at the control point. The EMG activity wits interpreted as end-plate noise or spi kes or both. The TrP Root Mean Square amplitudes were significantly higher than at the control points. Conclusion: Our investigation has demonstrated the presence of spontaneous EMG activity in myofascial TrPs, probably reflecting end-plate activity. (C ) 2001 by The Haworth Press, Inc. All rights reserved.