A laboratory study to quantify the biomechanical responses to whole-body vibration: The influence on balance, reflex response, muscular activity and fatigue

To determine the acute effects of whole-body vibration (WBV) on the sensorimotor system and potentially on the stability of the spine, different biomechanical responses were tested before and after 60 min of sitting, with and without vertical WBV, on four different days. Postures adopted while sitting and the simulated WBV exposure corresponded to large mining load haul dump (LHD) vehicles as measured in the field. Twelve males performed trials of standing balance on a force plate and a sudden loading perturbation test to assess back muscle reflex response, using surface electromyography (EMG). This latter test also allowed to assess if any muscle fatigue occurred as a result of the exposure. First of all, it was shown that back muscle activity while sitting with vibration was significantly higher as compared to back muscle activity while sitting with no vibration. However, WBV per se elicited very few effects on the other outcome variables and thus not supporting our hypothesis that WBV had any effect on spinal stability. Though WBV may not have elicited any effects, new findings have emerged concerning the effect of sitting on muscle fatigue and balance. It was shown that sustaining trunk sitting postures corresponding to mining vehicle operators generate back muscle fatigue. Unexpectedly, standing balance was also improved. The possible explanations and relevance of these findings are discussed.Relevance to industryOccupational groups exposed to WBV while sitting are at increased risk for low back disorders. The results of this study do not support the possible injury pathway linking WBV and back pain via sensorimotor deficits. Unexpectedly, it appears that sitting per se may affect the sensorimotor system but this may only apply to sitting postures corresponding to driving mining vehicles.