title: Effect of static neck flexion in cervical flexion-relaxation phenomenon in healthy males and females.
abstract: BACKGROUND
  Neck pain is a common musculoskeletal disorder, especially among skilled workers who must keep their necks in a flexed position frequently during the day. The present study investigated changes in cervical flexion-relaxation phenomenon parameters after sustained neck flexion.
  
  
  METHODS
  The participants were 40 healthy subjects grouped by gender (20 females, 20 males). They were exposed to static neck flexion at the full angle of cervical flexion for 10 min. Each subject underwent three trials of cervical flexion and re-extension before and after this period. Differences in onset and cessation angle of flexion-relaxation phenomenon, maximum neck flexion angle, amplitude of neck muscle activation and flexion-relaxation ratio were evaluated.
  
  
  RESULTS
  The maximum neck flexion angle significantly increased after sustained flexion. The onset of flexion-relaxation was significantly delayed during flexion, but cessation angle remained unchanged. Myoelectric activity of the cervical erector spinae muscles increased significantly after maintaining flexion, especially in female subjects. The flexion-relaxation ratio also decreased significantly.
  
  
  CONCLUSIONS
  It was concluded that 10 min of static flexion results in a delay in flexion-relaxation phenomenon and a shortened silence period. Also the cervical erector spinae muscles are required to be active longer and generate more activity. These neuromuscular changes may be a risk factor for neck pain.
authors.affiliation: Department of Physical Therapy, School of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran. Electronic address: r-mousavi@razi.tums.ac.ir.
authors.forename: Roghayeh
authors.initials: R
authors.lastname: Mousavi-Khatir
authors.affiliation: Department of Physical Therapy, School of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran. Electronic address: talebian@sina.tums.ac.ir.
authors.forename: Saeed
authors.initials: S
authors.lastname: Talebian
authors.affiliation: Department of Physical Therapy, School of Rehabilitation, Iran University of Medical Sciences, Tehran, Iran. Electronic address: maroufi.n@iums.ac.ir.
authors.forename: Nader
authors.initials: N
authors.lastname: Maroufi
authors.affiliation: Department of Physical Therapy, School of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran. Electronic address: olyaeigh@sina.tums.ac.ir.
authors.forename: Gholam Reza
authors.initials: GR
authors.lastname: Olyaei
mesh_terms: D000328:Adult; D002574:Cervical Vertebrae / Q000502:physiology*; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D009334:Neck Muscles / Q000502:physiology*; D019547:Neck Pain / Q000503:physiopathology; D011187:Posture / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology*; D055815:Young Adult
keywords: Cervical spine; Electromyography; Flexion-relaxation phenomenon; Neck pain