title: Neck muscle fatigue alters the cervical flexion relaxation ratio in sub-clinical neck pain patients.
abstract: BACKGROUND
  The cervical flexion relaxation ratio is lower in neck pain patients compared to healthy controls. Fatigue modulates the onset and offset angles of the silent period in both the lumbar and cervical spine in healthy individuals; however, this response has not been studied with neck pain patients. The purpose of this study was to determine if cervical extensor fatigue would alter the parameters of the cervical flexion relaxation more in a neck pain group than a healthy control group.
  
  
  METHODS
  Thirteen healthy and twelve neck pain patients participated. Cervical extensor activity was examined bilaterally and kinematics of the neck and head were collected. An isometric, repetitive neck extension task at 70% of maximum elicited fatigue. Participants performed 3 trials of maximal cervical flexion both pre and post fatigue.
  
  
  RESULTS
  The healthy controls and neck pain groups fatigued after 56 (41) and 39 (31) repetitions, respectively. There was a significant interaction effect for the flexion relaxation ratio between the control and neck pain groups from pre to post fatigue trials (F1,96=22.67, P=0.0001), but not for onset and offset angles (F1, 96=0.017, P=0.897), although the onset and offset angles did decrease significantly for both groups following fatigue (F1,96=9.26, P=0.002).
  
  
  CONCLUSIONS
  Individuals with mild to moderate neck pain have significant differences in their neuromuscular control relative to controls, experienced myoelectric fatigue with fewer repetitions in a shorter time, had a lower cervical flexion relaxation ratio at baseline and had an inability to decrease this ratio further in response to fatigue.
authors.affiliation: Faculty of Health Sciences, University of Ontario Institute of Technology, 2000 Simcoe St. North, Oshawa, ON L1H 7K4, Canada. Electronic address: mahboobehhosseinian@gmail.com.
authors.forename: Mahboobeh
authors.initials: M
authors.lastname: Zabihhosseinian
authors.affiliation: Faculty of Health Sciences, University of Ontario Institute of Technology, 2000 Simcoe St. North, Oshawa, ON L1H 7K4, Canada. Electronic address: Michael.Holmes@uoit.ca.
authors.forename: Michael W R
authors.initials: MW
authors.lastname: Holmes
authors.affiliation: Department of Graduate Studies, Canadian Memorial Chiropractic College, 6100 Leslie St, North York, ON M2H 3J1, Canada. Electronic address: BFerguson@cmcc.ca.
authors.forename: Brad
authors.initials: B
authors.lastname: Ferguson
authors.affiliation: Faculty of Health Sciences, University of Ontario Institute of Technology, 2000 Simcoe St. North, Oshawa, ON L1H 7K4, Canada. Electronic address: Bernadette.Murphy@uoit.ca.
authors.forename: Bernadette
authors.initials: B
authors.lastname: Murphy
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D016022:Case-Control Studies; D002574:Cervical Vertebrae / Q000502:physiology*; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D009068:Movement; D018763:Muscle Fatigue / Q000502:physiology*; D009334:Neck Muscles / Q000502:physiology*; D019547:Neck Pain / Q000503:physiopathology*; D055815:Young Adult
keywords: Cervical extensor muscles; Fatigue; Flexion relaxation phenomenon; Flexion relaxation ratio; Subclinical neck pain