title: Anatomy and biomechanics of the back muscles in the lumbar spine with reference to biomechanical modeling.
abstract: METHODS
  This article describes the development of a musculoskeletal model of the human lumbar spine with focus on back muscles. It includes data from literature in a structured form.
  
  
  OBJECTIVE
  To review the anatomy and biomechanics of the back muscles related to the lumbar spine with relevance for biomechanical modeling.
  
  
  BACKGROUND
  To reduce complexity, muscle units have been incorporated in an abridged manner, reducing their actions more or less to a single force equivalent. In early models of the lumbar spine, this may have been a necessary step to reduce complexity and, thereby, calculation time. The muscles of the spine are well described in the literature, but mainly qualitatively. Most of the literature provides a description of the structures without precise data of fiber length, muscle length, cross-sectional areas, moment arms, forces, etc. The predicted output of musculoskeletal models is very much dependent on the input parameters. The information needed to improve models consists of better approximations of the attachments to the vertebrae, and more precise data.
  
  
  METHODS
  Review of literature.
  
  
  RESULTS
  The predicted output of musculoskeletal models is very much dependent on the input parameters. Moderate changes in the assumed muscle line-of-action (i.e., moment arm) could substantially alter the magnitudes of predicted muscle and spinal forces, while the choice of optimization formulation is less sensitive.
  
  
  CONCLUSIONS
  Input parameters, moment arms, as well as physiologic cross-sectional areas have a profound effect on the predicted muscle forces. Therefore, it is important to choose the values for moment arm and physiologic cross-sectional area carefully because they are essential input parameters to biomechanical models.
authors.affiliation: Institute of Medical Anatomy, Biomech. and Motor Control, University of Copenhagen, Denmark. LHA@ami.dk
authors.forename: Lone
authors.initials: L
authors.lastname: Hansen
authors.forename: Mark
authors.initials: M
authors.lastname: de Zee
authors.forename: John
authors.initials: J
authors.lastname: Rasmussen
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Andersen
authors.forename: Christian
authors.initials: C
authors.lastname: Wong
authors.forename: Erik B
authors.initials: EB
authors.lastname: Simonsen
mesh_terms: D001415:Back; D001696:Biomechanical Phenomena; D006801:Humans; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000502:physiology*