Abstract
The aim of this study was to evaluate intramuscular muscle activity from a latent
myofascial trigger point (MTP) in a synergistic muscle during isometric muscle contraction.
Intramuscular activity was recorded with an intramuscular electromyographic (EMG)
needle inserted into a latent MTP or a non-MTP in the upper trapezius at rest and
during isometric shoulder abduction at 90° performed at 25% of maximum voluntary contraction
in 15 healthy subjects. Surface EMG activities were recorded from the middle deltoid
muscle and the upper, middle, and lower parts of the trapezius muscle. Maximal pain
intensity and referred pain induced by EMG needle insertion and maximal pain intensity
during contraction were recorded on a visual analog scale. The results showed that
higher visual analog scale scores were observed following needle insertion and during
muscle contraction for latent MTPs than non-MTPs (P < .01). The intramuscular EMG activity in the upper trapezius muscle was significantly
higher at rest and during shoulder abduction at latent MTPs compared with non-MTPs
(P < .001). This study provides evidence that latent MTPs are associated with increased
intramuscular, but not surface, EMG amplitude of synergist activation. The increased
amplitude of synergistic muscle activation may result in incoherent muscle activation
pattern of synergists inducing spatial development of new MTPs and the progress to
active MTPs.
Perspective
This article presents evidence of increased intramuscular, but not surface, muscle
activity of latent MTPs during synergistic muscle activation. This incoherent muscle
activation pattern may overload muscle fibers in synergists during muscle contraction
and may contribute to spatial pain propagation.
Key words
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Article info
Publication history
Published online: November 04, 2013
Accepted:
October 24,
2013
Received in revised form:
October 15,
2013
Received:
September 12,
2013
Footnotes
This study is supported by Danish Working Environment Foundation.
The authors have no conflicts of interest to report.
Identification
Copyright
© 2014 American Pain Society. Published by Elsevier Inc. All rights reserved.
