title: When exposed to challenged ventilation, those with a history of LBP increase spine stability relatively more than healthy individuals.
abstract: OBJECTIVE
  To determine if spine stability would be affected by the competing demands of simultaneous challenged ventilation and supporting a hand-held load.
  
  
  METHODS
  Subjects were their own controls in a repeated measures design where a single task was repeated, once in a different condition, in a random order.
  
  
  BACKGROUND
  Muscle stiffness influences spine stability. The same muscles that contribute to spine stability assist in challenged breathing. We hypothesized that a challenged ventilation task would place low back pain (LBP) sufferers at risk of spine instability.
  
  
  METHODS
  Subjects (14 normal; 14 with low back pain) performed two trials with a 22kg hand-held weight and the trunk angled forward at 30 degrees . One trial was of 60s duration while breathing ambient air, the other of 70s duration, while breathing 10% carbon dioxide. Spine stability and compression were quantified, using an EMG assisted optimization model in both trials.
  
  
  RESULTS
  Contrary to expectation, spine stability increased during the challenged breathing trials compared to the ambient air condition for subjects with a history of low back pain when abdominal muscle activity was accounted for as a covariate.
  
  
  CONCLUSIONS
  Subjects with a history of low back pain had higher stability in challenged breathing trials, indicating that some active mechanism protects the spine for the LBP groups in challenging situations. This may be to provide some margin of safety for damaged passive tissues but could be adversely affected by fatigue in the longer term.
authors.affiliation: Faculty of Professional Schools, School of Human Kinetics, Laurentian University, Sudbury, Ontario, Canada P3C 1N8. sgrenier@laurentian.ca
authors.forename: S G
authors.initials: SG
authors.lastname: Grenier
authors.forename: S M
authors.initials: SM
authors.lastname: McGill