title: Cardiovascular and muscle activity during chewing in whiplash-associated disorders (WAD).
abstract: OBJECTIVE
  The present study aimed to elucidate possible physiological mechanisms behind impaired endurance during chewing as previously reported in WAD. We tested the hypothesis of a stronger autonomic reaction in WAD than in healthy subjects in response to dynamic loading of the jaw-neck motor system.
  
  
  METHODS
  Cardiovascular reactivity, muscle fatigue indicies of EMG, and perceptions of fatigue, exhaustion and pain were assessed during standardised chewing. Twenty-one WAD subjects and a gender/age matched control group participated. Baseline recordings were followed by two sessions of alternating unilateral chewing of a bolus of gum with each session followed by a rest period.
  
  
  RESULTS
  More than half of the WAD subjects terminated the test prematurely due to exhaustion and pain. In line with our hypothesis the chewing evoked an increased autonomic response in WAD exhibited as a higher increase in heart rate as compared to controls. Furthermore, we saw consistently higher values of arterial blood pressure for WAD than for controls across all stages of the experiment. Masseter EMG did not indicate muscle fatigue nor were there group differences in amplitude and mean power frequency. Pain in the WAD group increased during the first session and remained increased, whereas no pain was reported for the controls.
  
  
  CONCLUSIONS
  More intense response to chewing in WAD might indicate pronounced vulnerability to dynamic loading of the jaw-neck motor system with increased autonomic reactivity to the test. Premature termination and autonomic involvement without EMG signs of muscle fatigue may indicate central mechanisms behind insufficient endurance during chewing.
authors.affiliation: Centre for Musculoskeletal Research, University of Gavle, Sweden.
authors.forename: Nebojsa
authors.initials: N
authors.lastname: Kalezic
authors.forename: Yuka
authors.initials: Y
authors.lastname: Noborisaka
authors.forename: Minori
authors.initials: M
authors.lastname: Nakata
authors.forename: Albert G
authors.initials: AG
authors.lastname: Crenshaw
authors.forename: Stefan
authors.initials: S
authors.lastname: Karlsson
authors.forename: Eugene
authors.initials: E
authors.lastname: Lyskov
authors.forename: Per-Olof
authors.initials: PO
authors.lastname: Eriksson
mesh_terms: D000328:Adult; D001341:Autonomic Nervous System / Q000503:physiopathology; D001794:Blood Pressure; D016022:Case-Control Studies; D003799:Dental Stress Analysis; D004576:Electromyography; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008406:Masseter Muscle / Q000503:physiopathology; D008409:Mastication / Q000502:physiology*; D018763:Muscle Fatigue; D009334:Neck Muscles / Q000503:physiopathology*; D019547:Neck Pain; D010807:Physical Endurance; D020069:Shoulder Pain; D014911:Whiplash Injuries / Q000503:physiopathology*