Abstract
The aim of this study was to evaluate motor unit activity from a latent myofascial
trigger point (MTP) in an antagonist muscle during isometric agonist muscle contraction.
Intramuscular activity was recorded with an intramuscular electromyographic (EMG)
needle inserted into a latent MTP or a non-MTP in the posterior deltoid muscle at
rest and during isometric shoulder flexion performed at 25% of maximum voluntary contraction
in 14 healthy subjects. Surface EMGs were recorded from the anterior and posterior
deltoid muscles. Maximal pain intensity and referred pain induced by EMG needle insertion
were recorded on a visual analogue scale. The results showed that higher local pain
was observed following needle insertion into latent MTPs (4.64 ± .48 cm) than non-MTPs
(2.35 ± .43 cm, P < .005). Referred pain was reported in 6/14 subjects following needle insertion into
latent MTPs, but none into the non-MTPs. The intramuscular EMG activity, but not surface
EMG activity, in the antagonist muscle was significantly higher at rest and during
shoulder flexion at latent MTPs than non-MTPs (P < .05). The current study provides the first evidence that increased motor unit excitability
is associated with reduced antagonist reciprocal inhibition.
Perspective
This study shows that MTPs are associated with reduced efficiency of reciprocal linhibition,
which may contribute to the delayed and incomplete muscle relaxation following exercise,
disordered fine movement control, and unbalanced muscle activation. Elimination of
latent MTPs and/or prevention of latent MTPs from becoming active may improve motor
functions.
Key words
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Article info
Publication history
Published online: November 14, 2011
Accepted:
September 15,
2011
Received in revised form:
August 11,
2011
Received:
June 27,
2011
Footnotes
This study is supported by Danish Agency for Science, Technology and Innovation: 07-028674-1.
The authors have no conflicts of interest to report.
Identification
Copyright
© 2011 American Pain Society. Published by Elsevier Inc. All rights reserved.
