This study characterized postural responses in subjects with (n=26, 39 ± 13 yrs) and without (n=24, 32 ± 10 yrs) chronic ( >6 months), recurrent low back pain (LBP) in response to support surface translations, randomly delivered in 12 different horizontal directions. Using kinematic, force plate and anthropometric data, the net center of pressure (CP), total body center of mass (CM), and net joint torques (sagittal and frontal planes) at the ankle, knee, hip and trunk were examined to characterize the neuromuscular responses in the two subject groups. LBP subjects exhibited larger anterior and posterior CM displacements compared to NLBP (p = 0.0267) and smaller anterior and posterior CP displacements (p < 0.0001). Overall, torque responses in persons with LBP were smaller, delayed and developed more quickly compared to NLBP subjects and the responses were non-directionally specific. These data suggest the automatic postural control of subjects with LBP is altered such that there is an overall stiffening strategy for LBP subjects, which is reflected in the reduced CP displacement and the smaller and delayed torque responses.
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