When exposed to challenged ventilation, those with a history of LBP increase spine stability relatively more than healthy individuals

Objective To determine if spine stability would be affected by the competing demands of simultaneous challenged ventilation and supporting a hand-held load. Design 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 22 kg hand-held weight and the trunk angled forward at 30°. One trial was of 60 s duration while breathing ambient air, the other of 70 s duration, while breathing 10% carbon dioxide. Spine stability and compression were quantified, using an EMG assisted optimization model in both trials. Findings 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. Interpretation 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.