Abstract
Background
Exposure to whole body vibration (WBV) is common in construction, agriculture, mining, and transportation. There is strong epidemiological evidence linking WBV with adverse health outcomes in the long-term, including low back pain. Fortunately, WBV exposure guidelines to prevent long-term musculoskeletal disorders and discomfort exist. In the shorter-term, it has been speculated that occupational levels of WBV may lead to increased risk of vehicle accidents and falls during egress; however, the acute effects of different vibration intensities remain poorly understood and it is uncertain whether established standards protect the worker from injurious short-term effects.
Objective
The aim of this study was to investigate the acute sensorimotor, physical, and cognitive effects of occupationally-relevant, simulated whole body vibration (WBV) at levels equivalent to international standard guideline thresholds for long-term discomfort and musculoskeletal disorder risk.
Method
Eighteen participants were recruited to perform four, 60-min conditions: (i) Control—no vibration, (ii) Low vibration—equivalent to the exposure action value, (iii) Shock—transient impacts at 1-min intervals superimposed on the Low condition, and (iv) High vibration—equivalent to the exposure limit value. Whole body vibration was simulated using data based on field-collected accelerations experienced by rural workers while operating an all-terrain vehicle. This vibration signal was manipulated to achieve required intensities for each condition and simulated with a 6 degree-of-freedom hexapod platform. Before and after each condition, we collected: rating of perceived body discomfort, rating of perceived headache, postural sway, blink frequency, King-Devick test, and psychomotor vigilance task. Pre- and post-condition data in each condition were submitted to either a paired
t-test (parametric) or Wilcoxon signed-rank test (non-parametric). To determine differences between conditions, each condition's post-condition data was normalized to its pre-condition value and entered as the dependent variable in a repeated measures analysis of variance.
Results
All conditions, including Control, led to increased upper body discomfort when compared to pre-exposure baseline. The Low condition led to increased discomfort in seven body locations, headache (91% increase from baseline;
t = −2.44,
P = 0.03), and postural imbalance (53% increase from baseline;
t = −2.88,
P = 0.01), but the effect on cognitive functioning was less clear. Shock condition led to whole body discomfort, specifically at nine upper body and lower body locations. The High condition led to increased whole body discomfort at all 10 body locations, headache (154% increase from baseline;
t = −2.91,
P = 0.01), postural imbalance (61% increase from baseline;
t = −2.57,
P = 0.02), and decrements in vigilance (mean reaction time: 6% increase from baseline,
t = −3.27,
P = 0.005; Number of lapses: 100% increase from baseline,
S = −42.5,
P = 0.002).
Conclusion
Although the number of pre-post condition effects increased with higher vibration intensity, these effects were not significantly different from sitting without vibration. Therefore, current guideline thresholds might not protect the worker from acute WBV effects. However, further research is needed to discern these effects from other sources of WBV. Based on this study, future WBV interventions and action controls should not only address vibration reduction, but also consider potential effects from prolonged sitting.
