Increased spontaneous electrical activity at a latent myofascial trigger point after nociceptive stimulation of another latent trigger point.
OBJECTIVE
To investigate the changes in surface and intramuscular electromyographic (EMG) activity at latent trigger points (TrPs) in the extensor carpi radialis brevis muscle after injection of either glutamate or isotonic saline into latent TrPs in the infraspinatus muscle.


METHODS
Nociceptive muscle stimulation was obtained by a bolus injection of glutamate (0.2 mL, 0.5 M) into a latent TrP located in the right infraspinatus muscle in 12 healthy volunteers. A bolus of isotonic saline (0.9%, 0.2 mL) injection served as control. Injections were guided by intramuscular EMG showing resting spontaneous electrical activity at the latent myofascial TrP in the infraspinatus muscle. Intramuscular (at the TrP) and surface EMG activities of both infraspinatus and extensor carpi radialis brevis muscles were recorded before, during, and after injection for a period of 6 minutes to monitor changes produced in EMG activity.


RESULTS
Glutamate injection into latent TrPs induced higher pain intensity than isotonic saline injection (P<0.001). The analysis of variance showed a significant increase in root mean square score of intramuscular EMG activity at TrP in the extensor carpi radialis brevis after glutamate (mean+/-SD: 212.0+/-215.6 microV) but not isotonic saline (mean+/-SD: 74.2+/-72.2 microV) injections (P<0.001). No changes in surface EMG activity were found. No significant changes in root mean square of intramuscular and surface EMG activity in the infraspinatus muscle were found.


CONCLUSIONS
Our results show that an increased nociceptive activity at latent TrPs in the infraspinatus muscle may increase motor activity and sensitivity of a TrP in distant muscles at a same segmental level.
Fernández-Carnero
Josué
J
Center for Sensory-Motor Interaction (SMI), Department of Health Science and Technology, Aalborg University, DK-9220 Aalborg, Denmark.
Ge
Hong-You
HY
Kimura
Yoshiyuki
Y
Fernández-de-Las-Peñas
César
C
Arendt-Nielsen
Lars
L
D000328:Adult; D000704:Analysis of Variance; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods; D005071:Evoked Potentials / Q000187:drug effects / Q000502:physiology*; D005260:Female; D005542:Forearm; D018698:Glutamic Acid / Q000009:adverse effects / Q000494:pharmacology; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects / Q000503:physiopathology*; D009209:Myofascial Pain Syndromes / Q000139:chemically induced / Q000473:pathology* / Q000503:physiopathology*; D010147:Pain Measurement / Q000379:methods; D017288:Pain Threshold / Q000187:drug effects / Q000502:physiology; D055815:Young Adult
D018698:Glutamic Acid