title: Flexion-relaxation response to static lumbar flexion in males and females.
abstract: OBJECTIVE
  To determine if creep developed in the lumbar viscoelastic tissues during a period of static flexion elicited changes in the muscular responses of the flexion-relaxation phenomenon.
  
  
  BACKGROUND
  Static lumbar flexion is a risk factor in workers, yet the physiological biomechanical and histological processes active in the evolution of the consequent low back disorder were not demonstrated experimentally. Controlled animal studies show that static lumbar flexion develops creep in the associated viscoelastic tissues and elicits spasms and modification of muscle function. Such neuromuscular changes are to be investigated in this study while assessing normal human subjects via the flexion-relaxation phenomenon.
  
  
  METHODS
  Male and female subject groups performed three bouts of lumbar flexion-extension before and after a 10 min period of static lumbar flexion. The surface electromyographic from the erector spinae muscles as well as flexion angle were recorded. The angle in which electromyographic diminished during flexion and initiated during extension was determined and subjected to ANOVA with repeated measures to determine any significant changes in the flexion-relaxation response.
  
  
  RESULTS
  The erector spinae were active through a significantly larger angle during flexion and initiated activity significantly earlier during extension after static flexion. Females demonstrated more pronounced changes than males. EMG amplitude did not change significantly. Spasms were recorded in more than half of the subjects during the static flexion period.
  
  
  CONCLUSIONS
  Creep developed during a short static lumbar flexion elicited significant changes in the muscular activity pattern of the flexion-relaxation phenomenon. The muscles seem to compensate for the loss of tension in the lumbar viscoelastic tissues, while spasms suggest that some micro-damage was incurred to the viscoelastic tissues.
  
  
  CONCLUSIONS
  Static lumbar flexion is shown experimentally as an activity that constitutes an occupational risk factor for the development of low back disorder.
authors.affiliation: Occupational Medicine Research Center, Bioengineering Laboratory, Department of Orthopaedic Surgery, Louisiana State University Health Sciences Center, 2025 Gravier Street, Suite 400, New Orleans, LA 70112, USA. msolom@lsuhsc.edu
authors.forename: Moshe
authors.initials: M
authors.lastname: Solomonow
authors.forename: Richard V
authors.initials: RV
authors.lastname: Baratta
authors.forename: Anthony
authors.initials: A
authors.lastname: Banks
authors.forename: Curt
authors.initials: C
authors.lastname: Freudenberger
authors.forename: Bing He
authors.initials: BH
authors.lastname: Zhou
mesh_terms: D000328:Adult; D004548:Elasticity; D004576:Electromyography / Q000379:methods; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008159:Lumbar Vertebrae / Q000502:physiology*; D008297:Male; D009068:Movement / Q000502:physiology*; D009126:Muscle Relaxation / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D011187:Posture / Q000502:physiology; D016059:Range of Motion, Articular / Q000502:physiology*; D012399:Rotation; D012737:Sex Factors; D014783:Viscosity