title: Trunk Dynamics Are Impaired in Ballet Dancers with Back Pain but Improve with Imagery.
abstract: OBJECTIVE
  Trunk control is essential in ballet and may be compromised in dancers with a history of low back pain (LBP) by associated changes in motor control. This study aimed to compare trunk mechanical properties between professional ballet dancers with and without a history of LBP. As a secondary aim, we assessed whether asking dancers to use motor imagery to respond in a "fluid" manner could change the mechanical properties of the trunk and whether this was possible for both groups.
  
  
  METHODS
  Trunk mechanical properties of stiffness and damping were estimated with a linear second-order system, from trunk movement in response to perturbations, in professional ballet dancers with (n = 22) and without (n = 8) a history of LBP. The second-order model adequately described trunk movement in response to the perturbations. Trials were performed with and without motor imagery to respond in a fluid manner to the perturbation.
  
  
  RESULTS
  Dancers with a history of LBP had lower damping than dancers without LBP during the standard condition (P = 0.002) but had greater damping during the "fluid" condition (P < 0.001), with values similar to dancers without LBP (P = 0.226). Damping in the dancers without LBP was similar between the conditions (P > 0.99). Stiffness was not different between the dancers with and those without a history of LBP (P = 0.252) but was less during the fluid condition than the standard condition (P < 0.001).
  
  
  CONCLUSIONS
  Although dancers with a history of LBP have less trunk damping than those without LBP, they have the capacity to modulate the trunk's mechanical properties to match that of pain-free dancers by increasing damping with motor imagery. These observations have potential relevance for LBP recurrence and rehabilitation.
authors.affiliation: 1NHMRC Centre of Clinical Research Excellence in Spinal Pain, Injury and Health, School of Health and Rehabilitation Sciences, The University of Queensland, Brisbane, Queensland, AUSTRALIA; and 2School of Physiotherapy, Faculty of Health Sciences, Australian Catholic University, Brisbane, Queensland, AUSTRALIA.
authors.forename: Jan E
authors.initials: JE
authors.lastname: Gildea
authors.forename: Wolbert
authors.initials: W
authors.lastname: VAN DEN Hoorn
authors.forename: Julie A
authors.initials: JA
authors.lastname: Hides
authors.forename: Paul W
authors.initials: PW
authors.lastname: Hodges
mesh_terms: D000328:Adult; D001416:Back Pain / Q000503:physiopathology*; D003615:Dancing; D004185:Disability Evaluation; D004576:Electromyography; D005260:Female; D006801:Humans; D007092:Imagination / Q000502:physiology*; D008297:Male; D009048:Motor Skills / Q000502:physiology*; D009068:Movement / Q000502:physiology*; D011214:Practice, Psychological; D011795:Surveys and Questionnaires; D060726:Torso / Q000502:physiology*; D055815:Young Adult