title: Effect of trunk flexion on cervical muscle EMG to rear impacts.
abstract: OBJECTIVE
  To determine the effect of occupant positioning on the response of the cervical muscles to whiplash-type posterolateral impacts.
  
  
  METHODS
  Twenty healthy volunteers underwent left posterolateral whiplash-type impacts with the volunteers seated "out-of-position". Electromyograms of the cervical muscles were recorded.
  
  
  RESULTS
  Whether having the trunk flexed to the left or right at the time of impact, the muscle responses were low in magnitude, showing a trend to increasing EMG responses with increasing acceleration (P>0.05). The time to onset and time to peak electromyogram for most muscles showed a trend to progressively decrease with increasing levels of acceleration. With the subject flexed to the left, all muscles generated 31% or less of the maximal voluntary contraction electromyogram. With the subject flexed to the right, all muscles generated 27% or less of their maximal electromyogram. In both positions, the trapezii were the most active (P<0.05). Thus, having the trunk flexed out of neutral posture at the time of impact produces a very low magnitude cervical muscle response compared to impacts with the trunk in neutral posture.
  
  
  CONCLUSIONS
  In the absence of bodily impact, the flexed trunk posture appears to produce a biomechanical response that would probably decrease the likelihood of cervical muscle injury in low velocity posterolateral impacts.
authors.affiliation: Department of Physical Therapy, Faculty of Rehabilitation Medicine, University of Alberta, Edmonton, Alberta, Canada T6G 2G4. shrawan.kumar@ualberta.ca
authors.forename: Shrawan
authors.initials: S
authors.lastname: Kumar
authors.forename: Robert
authors.initials: R
authors.lastname: Ferrari
authors.forename: Yogesh
authors.initials: Y
authors.lastname: Narayan
mesh_terms: D001696:Biomechanical Phenomena; D004576:Electromyography; D006801:Humans; D009334:Neck Muscles / Q000502:physiology*; D011187:Posture; D013997:Time Factors; D014911:Whiplash Injuries / Q000503:physiopathology*