Failure to Use Movement in Postural Strategies Leads to Increased Spinal Displacement in Low Back Pain

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Lumbar and hip movements, before and in response to rapid bilateral arm flexion, were evaluated in 10 people with recurrent low back pain (LBP) and 10 matched control subjects when standing on a flat surface or short base. To evaluate the preparatory movement and resultant displacement of the lumbopelvic region associated with internal perturbation in people with or without LBP. Strategies to control the trunk involve movement. Small spinal movements (preparatory movement), opposite to the direction of reactive moments, precede voluntary arm movements in healthy individuals. However, people with LBP often use less spinal movement. We hypothesized that the tendency to reduce spinal motion in LBP may be associated with decreased preparatory motion, and this may counter intuitively lead to increased displacement of the trunk in response to arm movements. Movements at the lumbopelvic region before and in response to rapid bilateral arm flexion were examined using electromagnetic motion sensors when subjects were standing on a flat surface or short base. In control subjects, preparatory extension of the lumbar spine preceded a resultant flexion of the region in 88% of trials on the flat surface. People with LBP used preparatory extension less frequently (69%, P = 0.027). Consequently, the spinal displacement (resultant flexion) induced by shoulder flexion was significantly greater in the LBP group (3.2 degrees +/- 1.8 degrees) than controls (1.8 degrees +/- 1.6 degrees, P = 0.004). There was a significant correlation (r = 0.47) between preparatory and resultant movement of the lumbar spine in the LBP group, which indicates that subjects with reduced preparatory extension were more likely to have a greater resultant displacement. These data suggest that spinal movement is different in people with LBP, and reduced spinal movement in advance of predictable perturbation may be associated with compromised quality of trunk control.