title: Intervertebral stiffness of the spine is increased by evoked contraction of transversus abdominis and the diaphragm: in vivo porcine studies.
abstract: METHODS
  In vivo porcine study of intervertebral kinematics.
  
  
  OBJECTIVE
  This study investigated the effect of transversus abdominis and diaphragm activity, and increased intra-abdominal pressure on intervertebral kinematics in porcine lumbar spines.
  
  
  BACKGROUND
  Studies of trunk muscle recruitment in humans suggest that diaphragm and transversus abdominis activity, and the associated intra-abdominal pressure contribute to the control of intervertebral motion. However, this has not been tested in vivo.
  
  
  METHODS
  Relative intervertebral motion of the L3 and L4 vertebrae and the stiffness at L4 were measured in response to displacements of the L4 vertebra imposed via a device fixed to the L4 vertebral body. In separate trials, diaphragm and transversus abdominis activity was evoked by stimulation of the phrenic nerves and via electrodes threaded through the abdominal wall.
  
  
  RESULTS
  When intra-abdominal pressure was increased by diaphragm or transversus abdominis stimulation, the relative intervertebral displacement of the L3 and L4 vertebrae was reduced and the stiffness of L4 was increased for caudal displacements. There was no change in either parameter for rostral displacements. In separate trials, the diaphragm crurae and the fascial attachments of transversus abdominis were cut, but intra-abdominal pressure was increased. In these trials, the reduction in intervertebral motion was similar to trials with intact attachments for caudal motion, but was increased for rostral trials.
  
  
  CONCLUSIONS
  The results of these studies indicate that elevated intra-abdominal pressure, and contraction of diaphragm and transversus abdominis provide a mechanical contribution to the control of spinal intervertebral stiffness. Furthermore, the effect is modified by the muscular attachments to the spine.
authors.affiliation: Department of Physiotherapy, The University of Queensland, Brisbane, Australia. p.hodges@shrs.uq.edu.au
authors.forename: Paul
authors.initials: P
authors.lastname: Hodges
authors.forename: Allison
authors.initials: A
authors.lastname: Kaigle Holm
authors.forename: Sten
authors.initials: S
authors.lastname: Holm
authors.forename: Lars
authors.initials: L
authors.lastname: Ekström
authors.forename: Andrew
authors.initials: A
authors.lastname: Cresswell
authors.forename: Tommy
authors.initials: T
authors.lastname: Hansson
authors.forename: Alf
authors.initials: A
authors.lastname: Thorstensson
mesh_terms: D000009:Abdominal Muscles / Q000502:physiology*; D000818:Animals; D001696:Biomechanical Phenomena; D003964:Diaphragm / Q000502:physiology*; D004558:Electric Stimulation; D008159:Lumbar Vertebrae / Q000502:physiology; D009068:Movement; D009119:Muscle Contraction; D013131:Spine / Q000502:physiology*; D013552:Swine