Postural variability during pursuit tracking in low-back pain patients

Abstract

In low-back pain patients the somatosensory regulation of quiet stance is altered compared to healthy subjects which in turn results in larger variation in the postural control. In this study, 8 low back pain patients performed postural sways on a force plate to follow a squared shaped track on visual feedback corresponding to 20% of maximum sway in the 4 directions of forward, backward, left and right. The tracking was repeated 4 times and variability- and complexity measures of the center of pressure were calculated and the motor control learning effect was analyzed. The effect of epoch size on the statistical result was also investigated. As the main result through the four tracking trials, variability (calculated as standard deviation of the force output) decreased in both the anterior-posterior direction and the medial lateral direction (p<0.05) and complexity measures (calculated as both approximate entropy and sample entropy) increased for anterior-posterior direction and medial-lateral direction (p<0.05). Secondary, no effect was found for the analysis of different epoch sizes. Results show that a learning effect is present even for 4 repetitions of a postural tracking task. The results presented can be of relevance in training sessions for patients with impaired postural control. © 2011 Springer-Verlag.