The effect of alterations in the processing of proprioceptive signals, on postural control, has been studied using muscle vibration effects. However, reliability and agreement of muscle vibration have still to be addressed.This study aimed to assess intra- and interday reliability and agreement of vibration effects of lumbar paraspinal and triceps surae muscles in a non-selected sample of 20 subjects, standing on solid surface and on foam. We used mean position and velocity of Centre of Pressure (CoP), during and after vibration to quantify the effect of muscle vibration. We also calculated the ratio of vibration effects on the lumbar paraspinal and triceps surae muscles (proprioceptive weighting).Displacement of the CoP during vibration showed good reliability (ICCs. >. 0.6), and proprioceptive weighting of displacement fair to good reliability (0.52-0.73). Agreement measures were poor, with most CV's ranging between 18% and 36%. Change in CoP velocity appeared not to be reliable. Balance recovery, when based on CoP position and calculated a short period after cessation of vibration, showed good reliability. According to this study, displacement during vibration, proprioceptive weighting and selected recovery variables are the most reliable indicators of the response to muscle vibration.
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Patients with non-specific low back pain (LBP) may use postural control strategies that differ from healthy subjects. To study these possible differences, we measured the amount and structure of postural sway, and the response to muscle vibration in a working cohort of 215 subjects. Subjects were standing on a force plate in bipedal stance. In the first trial the eyes were open, no perturbation applied. In the following 6 trials, vision was occluded and subjects stood under various conditions of vibration/no vibration of the lumbar spine or m. Triceps Surae (TSM) on firm surface and on foam surface. We performed a factor analysis to reduce the large amount of variables that are available to quantify all effects. Subjects with LBP showed the same amount of sway as subjects without LBP, but the structure of their sway pattern was less regular with higher frequency content. Subjects with LBP also showed a smaller response to TSM vibration, and a slower balance recovery after cessation of vibration when standing on a solid surface. There was a weak but significant association between smaller responses to TSM vibration and an irregular, high frequency sway pattern, independent from LBP. A model for control of postural sway is proposed. This model suggests that subjects with LBP use more co-contraction and less cognitive control, to maintain a standing balance when compared to subjects without LBP. In addition, a reduced weighting of proprioceptive signals in subjects with LBP is suggested as an explanation for the findings in this study.
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A commentary on: Older adults can improve compensatory stepping with repeated postural perturbations by Dijkstra,B.W., Horak,F.B., Kamsma,Y.P.T., and Peterson,D.S.(2015).Front.AgingNeurosci. 7:201. doi:10.3389/fnagi.2015.00201. In sum, the results of Dijkstra etal. (2015) are of importance and significance for the field of falls prevention and stability control in aging. In particular, the work highlights the importance of multidirectional step or perturbation training, due to a lack of transfer across tasks. Whether this would hold for multidirectional gait perturbations is unclear, due to the influence of forward velocity during walking. Future work should explore different types, intensities and frequencies of perturbations in order to determine the most effective strategy for improving dynamic stability control in healthy older adults and inpatients with declined locomotor performance and increased falls risk. Finally, as Dijkstra etal. (2015) and previous studies found floor effects in the adaptation of young participants, further attempts should be made to appropriately scale perturbations to participant or groupability, in order to reliably compare adaptation across different groups.
