The Hong Kong Polytechnic University
Low back pain (LBP) is a common health problem with a high recurrence rate. Current treatments are not that effective. As patients with LBP are often found to be proprioception impaired, new proprioception exercises are required. Whole body vibration (WBV) stimulates proprioceptive receptors on the muscles, causing an alternation in muscle recruitment and hence modifying the muscle stiffness and joint stability. Its potential to improve muscle function and proprioception has been shown in athletes. Sinusoidal alternative WBV was shown to be able to relieve pain in patients with LBP after a long term application. However, the underlying mechanism has not been investigated. Another study has demonstrated that short term WBV had an immediate effect on improving pelvic repositioning ability on normal individuals. As spinal proprioception facilitates spine positioning and movement and computes self-coordination under both static and dynamic conditions, it is essential to investigate the effect of WBV on lumbo-pelvic stability, coordination and repositioning ability to justify whether WBV has a beneficial effect on spinal proprioception. In this study, the immediate and carryover effect of a 5-min 18Hz WBV on spinal proprioception were investigated. The study was divided into two stages. In the first stage, twenty young normal individuals were recruited and the effects of WBV in standing and seated postures on spinal proprioception were determined and compared. In the second stage, the effect of WBV on spinal proprioception was evaluated in eight individuals with LBP, with age matched with those in the healthy group, in seated posture. The results were compared with the healthy subjects receiving WBV in seated posture. In addition to quantifying body alignment, repositioning ability of participants before and after WBV, postural stability and phasic relationship between the lumbar and pelvis segments were investigated in terms of maximum reaching distance and lumbo-pelvic coordination using Dynamical Systems Theory approach. Assessments were conducted before, immediately after, 30 minutes after and 1 hour after 5 minutes of WBV (18Hz, 6mm p-p amplitude). Multivariate analysis of variance was used to study the changes of each variable and LSD criterion was adopted for post-hoc comparisons. In the first stage, it was shown that WBV in both standing and seated posture had significant beneficial effect on maximum reaching distance, dynamic lumbo-pelvic coordination and repositioning ability without significant group difference. Significant carryover effect of WBV was also shown. In the second stage, immediate improvement of postural control, lumbo-pelvic coordination and repositioning ability were observed for the LBP group. However, the effect seemed to be less long-lasting. There were limitations in the study. The effect of vibration intensity and learning effect have not been fully investigated. As analysis was limited to the sagittal plane, the effect of WBV on spinal motor control in other planes was not known.. In conclusion, 5 minutes of 18 Hz WBV was shown to have significant positive effect on lumbo-pelvic stability, coordination and repositioning ability without any apparent adverse effect in both normal and LBP individuals. The effects were more apparent and long-lasting when WBV was applied to healthy individuals than patients with LBP. Further clinical study on patients with LBP undergoing similar or different WBV protocol is recommended to confirm its clinical application on improving spinal proprioception.