title: Effects of changes in muscle activation level and spine and hip posture on erector spinae fiber orientation.
abstract: BACKGROUND
  During lumbar flexion, the fiber orientation of the lumbar erector spinae (LES) muscle becomes oriented more along the spine compressive axis. It is unknown how changes in LES activation effect fiber orientation.
  
  
  METHODS
  Ultrasound images of LES were collected during 2 sets of experimental conditions: (1) varying levels of LES activation while lying prone; and (2) varying spine and hip angles while seated. Electromyographic activity and lumbar spine and hip angles were also recorded.
  
  
  RESULTS
  As LES activation increased, increases in fiber orientation (signifying increased orientation along the posterior shear axis) were found (P<0.001). Compared with the relaxed sitting posture, decreases in fiber orientation were found with full spine flexion and combined spine and hip flexion (P<0.001), but there were no changes with full hip flexion alone.
  
  
  CONCLUSIONS
  Activation magnitude and spine posture both affect LES fiber orientation, thus modifying its ability to protect the spine against anterior shear forces.
authors.affiliation: Department of Human Health and Nutritional Sciences, University of Guelph, 50 Stone Road East, Guelph, Ontario N1G 2W1, Canada.
authors.forename: Alexandra B
authors.initials: AB
authors.lastname: Harriss
authors.forename: Stephen H M
authors.initials: SH
authors.lastname: Brown
mesh_terms: D064131:Back Muscles / Q000000981:diagnostic imaging / Q000502:physiology*; D001696:Biomechanical Phenomena / Q000502:physiology; D004576:Electromyography / Q000379:methods; D006615:Hip / Q000502:physiology*; D006801:Humans; D008159:Lumbar Vertebrae / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000000981:diagnostic imaging / Q000502:physiology*; D009949:Orientation / Q000502:physiology; D011187:Posture / Q000502:physiology*; D014463:Ultrasonography; D055815:Young Adult
keywords: EMG; lumbar erector spinae; muscle fiber orientation; spine; ultrasound