title: Altered neuromuscular control mechanisms of the trapezius muscle in fibromyalgia.
abstract: BACKGROUND
  fibromyalgia is a relatively common condition with widespread pain and pressure allodynia, but unknown aetiology. For decades, the association between motor control strategies and chronic pain has been a topic for debate. One long held functional neuromuscular control mechanism is differential activation between regions within a single muscle. The aim of this study was to investigate differences in neuromuscular control, i.e. differential activation, between myalgic trapezius in fibromyalgia patients and healthy controls.
  
  
  METHODS
  27 fibromyalgia patients and 30 healthy controls performed 3 minutes bilateral shoulder elevations with different loads (0-4 Kg) with a high-density surface electromyographical (EMG) grid placed above the upper trapezius. Differential activation was quantified by the power spectral median frequency of the difference in EMG amplitude between the cranial and caudal parts of the upper trapezius. The average duration of the differential activation was described by the inverse of the median frequency of the differential activations.
  
  
  RESULTS
  the median frequency of the differential activations was significantly lower, and the average duration of the differential activations significantly longer in fibromyalgia compared with controls at the two lowest load levels (0-1 Kg) (p < 0.04), but not at the two highest load levels (2 and 4 Kg).
  
  
  CONCLUSIONS
  these findings illustrate a different neuromuscular control between fibromyalgia patients and healthy controls during a low load functional task, either sustaining or resulting from the chronic painful condition. The findings may have clinical relevance for rehabilitation strategies for fibromyalgia.
authors.affiliation: National Research Centre for the Working Environment, Lersø Parkallé 105, DK-2100 Copenhagen, Denmark.
authors.forename: Björn
authors.initials: B
authors.lastname: Gerdle
authors.forename: Christer
authors.initials: C
authors.lastname: Grönlund
authors.forename: Stefan J
authors.initials: SJ
authors.lastname: Karlsson
authors.forename: Andreas
authors.initials: A
authors.lastname: Holtermann
authors.forename: Karin
authors.initials: K
authors.lastname: Roeleveld
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena / Q000502:physiology; D015897:Comorbidity; D004576:Electromyography; D005260:Female; D005356:Fibromyalgia / Q000503:physiopathology*; D006801:Humans; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology; D009068:Movement / Q000502:physiology; D009069:Movement Disorders / Q000175:diagnosis / Q000503:physiopathology*; D009119:Muscle Contraction / Q000502:physiology*; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation / Q000503:physiopathology*; D009469:Neuromuscular Junction / Q000502:physiology; D016059:Range of Motion, Articular / Q000502:physiology; D012782:Shoulder / Q000294:innervation / Q000503:physiopathology*; D016474:Weight-Bearing / Q000502:physiology