Article

Effects of local and remote muscle pain on human jaw reflexes evoked by fast stretches at different clenching levels.

Orofacial Pain Laboratory, Center for Sensory-Motor Interaction, Aalborg University, Denmark.
Experimental Brain Research (impact factor: 2.39). 09/2001; 139(4):495-502. pp.495-502
Source: PubMed

ABSTRACT Muscle pain imposes significant changes on natural motor tasks, but the consequences for stretch reflexes are still disputed. The present study examined the jaw reflexes to fast (10 ms) stretches of the mandible in an experimental model with local pain in the masseter muscle and remote pain in the tibialis anterior muscle. The stretch reflexes were elicited in healthy volunteers (n=13) before, during, and after periods with constant levels of experimental pain and while the subjects clenched at 0%, 15%, 30%, and 45% of the maximal voluntary contraction (MVC) levels. Surface electromyography (EMG) was used to record the reflex responses. Pain in the masseter muscle (mean +/- SEM, 3.8+/-0.4 on a 10-cm visual analogue scale), but not in the tibialis anterior muscle (3.4+/-0.3; paired t-test, P=0.318) was associated with significant changes in both prestimulus EMG activity (ANOVA, P=0.002) and in peak-to-peak amplitudes of the stretch reflex (ANOVA, P=0.022). However, when the changes in prestimulus EMG activity were taken into consideration a significant increase in the stretch reflex persisted in the painful muscle at 15% and 30% MVC. Local circuits at the trigeminal level involving the fusimotor system are proposed to mediate a significant part of this modulatory effect.

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Keywords

10-cm visual analogue scale
 
experimental model
 
experimental pain
 
healthy volunteers
 
Local circuits
 
local pain
 
modulatory effect
 
Muscle pain
 
natural motor tasks
 
painful muscle
 
paired t-test
 
peak-to-peak amplitudes
 
prestimulus EMG activity
 
reflex responses
 
remote pain
 
significant changes
 
significant part
 
subjects clenched
 
Surface electromyography
 
tibialis anterior muscle