Student Research: Molly Halverson

, Occupational & Environmental Exposure Sciences (OEES), 2013
Faculty Advisor: Peter W. Johnson

Evaluating Whole Body Vibration and Standing Balance Among Truck Drivers


Background: Over 60% of fatal fall-related occupational injuries occur in the long haul freight trucking industry. Exposure to whole body vibration (WBV) from driving or operating vehicles has been shown to negatively affect balance and may contribute to falls when entering or exiting the vehicle. Fall-related injuries are eight times more likely to occur upon exiting the vehicle than entering. It is hypothesized that WBV has a detrimental effect on postural stability upon truck egress and may be a contributing factor to falls when truck drivers egress their truck.

Methodology: Using field-collected WBV exposures from the floor of a truck cab, a three-dimensional vibrating platform (hexapod system) was used in a laboratory setting to expose eight truck drivers to two hours of simulated truck driving. The hexapod system provided an accurate and systematic method to simulate these vibrational exposures for the purpose of investigating whether balance changes occurred with prolonged exposure to WBV.

Using a repeated measures design, the truck drivers participated in two exposure levels: 1) sitting in an electromechanically active-suspension vibration-reducing seat, and 2) sitting in a standard passive, air-suspension truck seat. Based on field measurements, WBV exposures were expected to be approximately 50% lower in the seat with the electromechanically active-suspension. Seat order was randomized and counterbalanced. Immediately before exposure to WBV, after two hours of exposure, and five and ten minute post exposure, participants were asked to stand on a Wii balance board under two conditions, one with the eyes closed and the other with the eyes open. Each measurement lasted 30 seconds during which the standing balance center of pressure (COP) deviations were measured. In addition, a subcomponent of the Mini-BEST test, a qualitative clinical balance assessment tool, was performed to complement the quantitative force plate measurements.

Analysis: The association between exposure to WBV and postural instability was assessed pre- and post- WBV exposure, in the ten minutes post-exposure, and between the two different WBV exposures (the two seat conditions). Postural measurements of interest for the COP deviations focused on medio-lateral (ML) path length, anterior-posterior (AP) path length, and total path length. Secondary variables included the standard deviation of the AP and ML components. Other variables of interest included assessing the balance measurements with the eyes open/closed to determine whether the visual component of vibration, vestibular component, or both induced imbalance.

Results/Conclusions: Significant differences were found between all balance measurements (ML, AP, total path length) before and after WBV exposure for eyes open status but not eyes closed. Relative to the passive, air-suspension seat, the subjects’ WBV exposures were roughly 50% lower with the active suspension seat. The decrease in WBV exposure associated with sitting in the active suspension seat did not affect postural balance when compared to the passive, air-suspension seat. After 10 minutes post exposure, balance measurements (path lengths) had returned to baseline in the eyes open balance measurements but were better (shorter than baseline) in the eyes closed measurement.

Specific aims:
1. To determine whether there were changes in postural stability after exposing truck drivers to two hours of simulated exposure to whole body vibration.
2. If there were changes in postural stability, determine whether the recovery of standing balance occurs in a short period of time.
3. To determine whether there were differences in postural stability after exposing truck drivers to different levels of whole body vibration.
4. To determine whether there was a visual component which may affect postural stability by comparing postural stability with the eyes open and the eyes closed.