title: Experimental muscle pain results in reorganization of coordination among trapezius muscle subdivisions during repetitive shoulder flexion.
abstract: The aim of the study was to examine the effect of experimental unilateral upper trapezius muscle pain on the relative activation of trapezius muscle subdivisions bilaterally during repetitive movement of the upper limb. Surface EMG signals were detected from nine healthy subjects from the upper, middle and lower divisions of trapezius during a repetitive bilateral shoulder flexion task. Measurements were performed before and after injection of 0.5 ml hypertonic (pain condition) and isotonic (control) saline into the upper division of the right trapezius muscle in two experimental sessions. On the painful side, upper trapezius showed decreased EMG amplitude (average rectified value, ARV) and lower trapezius increased ARV throughout the entire task following the injection of hypertonic saline (40.0 +/- 22.2 vs. 26.0 +/- 17.4 microV, and 12.5 +/- 7.6 vs. 25.6 +/- 14.8 microV, respectively, at the beginning of the contraction). On the side contralateral to pain, greater estimates of ARV were identified for the upper division of trapezius as the task progressed (37.4 +/- 20.2 vs. 52.7 +/- 28.4 microV, at the end of the contraction). Muscle fiber conduction velocity did not change with pain in all three divisions of the right trapezius muscle. The results suggest that local elicitation of nociceptive afferents in the upper division of the trapezius induces reorganization in the coordinated activity of the three subdivisions of the trapezius in repetitive dynamic tasks.
authors.affiliation: Center for Sensory-Motor Interaction (SMI), Department of Health Science and Technology, Aalborg University, Fredrik Bajers Vej 7D-3, 9220, Aalborg, Denmark. deborahf@hst.aau.dk
authors.forename: Deborah
authors.initials: D
authors.lastname: Falla
authors.forename: Dario
authors.initials: D
authors.lastname: Farina
authors.forename: Thomas
authors.initials: T
authors.lastname: Graven-Nielsen
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D000344:Afferent Pathways / Q000502:physiology; D004576:Electromyography; D005246:Feedback / Q000502:physiology; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D018836:Inflammation Mediators / Q000009:adverse effects; D008297:Male; D009046:Motor Neurons / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation / Q000503:physiopathology*; D009431:Neural Conduction / Q000502:physiology; D009469:Neuromuscular Junction / Q000502:physiology; D009475:Neurons, Afferent / Q000502:physiology; D009619:Nociceptors / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D012462:Saline Solution, Hypertonic / Q000009:adverse effects; D012782:Shoulder / Q000502:physiology*; D020069:Shoulder Pain / Q000503:physiopathology*
chemical_list: D018836:Inflammation Mediators; D012462:Saline Solution, Hypertonic