title: Description of the relation between the forces acting in the lumbar spine and whole-body vibrations by means of transfer functions.
abstract: OBJECTIVE
  The purpose of this study was to display the relationships between the forces transmitted in the spine and the accelerations of the vibrating seat.
  
  
  BACKGROUND
  Investigations reveal that exposure to whole-body vibration can induce degenerative changes in the lumbar spine. Elevated spinal forces are probably the crucial component in the pathogenesis of this disease.
  
  
  METHODS
  The spinal forces are simulated by means of a biomechanical model, where 16 rigid bodies represent the upper body and the arms of a sitting operator. The relationships between seat accelerations and spinal forces are displayed as frequency-dependent transfer functions.
  
  
  RESULTS
  Spinal forces are not only elevated in the direction parallel to the vibration excitation but also in the two other orthogonal vibration directions. According to the magnitudes of the transfer functions the highest oscillating parts of the forces are reached at frequencies below 10 Hz.
  
  
  CONCLUSIONS
  Using the transfer functions, the time course of the spine forces can be computed and a new kind of weighting function can be derived which enables a force related weighting of the seat acceleration. RelevanceVibration induced health risks are commonly assessed by the weighted acceleration (ISO 2631-1). These weighting factors resulted from subjective magnitude sensation. It is argued that a more valid assessment will be obtained if the accelerations are weighted in relation to spinal forces. These forces cannot be measured directly under vibration. However, they can be simulated by means of biomechanical models.
authors.affiliation: Institut für Arbeitsphysiologie an der Universität Dortmund, Ardeystrasse 67, D-44139, Dortmund, Germany. fritz@arb-phys.uni-dortmund.de
authors.forename: M
authors.initials: M
authors.lastname: Fritz
mesh_terms: D000054:Acceleration; D006801:Humans; D008159:Lumbar Vertebrae / Q000502:physiology*; D008348:Manikins; D011187:Posture; D014732:Vibration