Abstract
Background: Driving a quad bike in a rural occupational setting is likely to expose the driver to various physical stimuli such as whole-body vibration (WBV), mechanical shock, vehicle roll and pitch, sustained or awkward sitting postures, engine noise, and extreme temperatures. These exposures may be linked to perturbed postural control and to increased risk of spinal disorder. The literature suggests vehicle and terrain induced WBVs have the potential to induce transient neurophysiological disturbances within the somatosensory, visual and vestibular systems, and thereby influence overall postural control of an individual. However, no studies have investigated how driving a quad bike influences overall postural control. The purpose of this thesis is to use a battery of postural tasks (static, dynamic and functional) to provide an understanding of how quad bike driving alters postural control in a group of rural workers. The thesis is based on three studies that seek to answer the research question: Do immediate or delayed postural control alterations occur following a period of controlled quad bike driving in healthy male rural workers?
Methods and results: Study 1 has systematically reviewed the literature on postural control following a period of exposure to occupational WBV. This review identified 2 field and 3 laboratory studies that investigated postural control during standing following occupational driving and/or WBV exposure and found moderate evidence towards the existence of negative postural control alterations in terms of increase in the magnitude of centre of pressure (COP) measures. No studies have investigated dynamic and functional postural control following WBV exposure and there is also a need for establishing the reliability of COP measures of a chosen battery of tasks in order to determine the true change in the magnitude of COP following occupational driving or WBV exposure.
Study 2 evaluated the reliability and systematic variation of COP measures recorded during the performance of a battery of tasks (bipedal and unipedal stance, limits of stability and lifting task) performed by a group of healthy males (n=36) on three independent occasions, within a single testing session. Twelve of the eighteen time-domain distance, area and hybrid-distance COP measures of the battery of tasks showed excellent relative (ICC values: ≥0.75) and acceptable absolute (SEM%: ≤15%) intra-session reliability in a group of healthy male individuals. However, a consequence of repeated testing occasions within a single testing session, demonstrated a significant (p≤0.05) systematic variation in unipedal stance (practice effects), and cumulative fatigue effects were observed in the lifting and limits of stability tasks. The presence of these effects required methodological adjustment of temporal parameters between the testing sessions in the study 3.
Study 3 explored postural control of rural workers (n=34) during the performance of a chosen battery of tasks, once before [Testing Session (TS)-I] the 30 minute quad bike driving session on a typical New Zealand terrain, and twice post-driving, once immediately following the driving session (TS-II) and delayed (TS-III), following the immediate testing session (TS-II). COP measures for each task were selected as dependent variables if they demonstrated excellent reliability and acceptable SEM% in the study 2. The results demonstrated significant (p<0.05) negative alterations (i.e. increase in the magnitude) in the COP measures of lifting task, and positive alterations (i.e. decrease in the magnitude) in the COP measures of unipedal stance (p<0.001) during both TS-II and TS-III when compared to TS-I. However significant (p<0.05) negative alterations in the COP measures of bipedal stance and leaning movements (a component of limits of stability task), and positive alterations in the leaning ranges (maximum stability limits) were demonstrated only in the TS-III when compared to TS-I. None of the COP measures of the postures maintained at the maximal stability limits (a component of limits of stability task) displayed alterations (p>0.05) in postural control following quad bike driving.
Conclusion: These results demonstrate a mixture of both immediate and delayed alterations in postural control following a period of occupational driving of a quad bike on a typical New Zealand farm terrain. Interestingly the results demonstrate both a worsening and improvement in postural control during the performance of a battery of tasks. Since the chosen study design for this thesis was a single group pretest-posttest pragmatic field experiment, other extraneous/confounding variables (motor learning/ fatigue influences/cognitive) could have influenced the results. It may be that NZ rural workers who regularly use quad bikes that expose them to high levels of WBV (+/- other physical exposures) are at risk of postural perturbations on a regular basis during both static, dynamic and functional tasks. Interestingly, these exposures can be either adverse or facilitatory in their postural effects and will require further laboratory based investigations of specific postures and vibration exposures in order to determine how such disparity can best be explained or challenged.