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Professional drivers of off-road vehicles, driving on irregular terrain such as in forestry, agriculture and mining, are exposed to whole-body vibration and mechanical shocks. These driver groups have reported severe musculoskeletal problems in the spine, but the association to seated postural reactions is not fully understood. One assumption is that unexpected shocks may create excessive load on spinal joints. The driver’s posture and exposure to mechanical shocks are required to be included in work risk assessments, but muscle activity and body kinematics are not included. The overall aim of this thesis was to describe and analyse seated postural reactions to mechanical shocks and to evaluate measuring of seated postures with relevance for risk assessment and the prevention of musculoskeletal disorders among drivers. The thesis includes four studies, all laboratory-based using a repeated-measures design. Postural reactions were recorded from 23 (Paper I) and 20 (Paper II & III) young, healthy male participants who were seated on a movable platform. The platform delivered mechanical shocks with peak accelerations up to 14 m/s2 in lateral directions during different conditions. Furthermore, twenty participants (Paper IV) were tested by four testers for analysis of test-retest reliability within and between testers measuring seated postures. Kinematics were here detected by means of a motion analysis system (MoLabTM) and described for the spine as angular displacements or range of motion (ROM) using a three-segment model of neck, trunk and pelvis (Paper I–III) and as a more specific model (Paper IV). Surface electromyography (EMG) was recorded bilaterally on the following muscles; trapezius upper part, upper neck, erector spinae and external oblique (Paper I–III). The general findings show that EMG amplitudes normalised to maximum voluntary contractions (MVC) did not exceed 2% in the trapezius, 8% in the upper neck and erector spinae and 18% in the external oblique. The EMG amplitudes and the angular displacements in the neck were significantly reduced from the first compared to the fifth mechanical shock. Adding a cognitive task significantly increased angular displacements. The largest ROM with approximately 20° in each segment was found during a double-sided mechanical shock (shock that changes direction). The reliability within one tester measuring seated postures was mostly considered good and superior to the reliability between several testers, but still insensitive to changes of less than 10°. Exposure to single-sided or double-sided mechanical shocks with accelerations up to 14 m/s2 seem not to cause postural reactions to such an extent that overload of muscles or joint structures should be expected. There seems to be a quick adaptation that causes an improved readiness. The external obliques were most active when restoring equilibrium and seem important for stabilising the whole spinal column. Stability training, in order to improve neuromuscular control of the external obliques could, therefore, be a possible recommendation. The angular displacement in the neck increases if the subject solves a cognitive task of why such activities should be avoided when driving in difficult terrains. Since accurate descriptions of the spinal posture seems difficult even when advanced technical equipment is used, simpler models seem more appropriate. The results show that postural control is maintained even when exposed to considerable mechanical shocks. On the basis of these results, there is no need to change established risk assessment models.

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The phrase “miner” is comparatively non-specific as mining is seen as a multi-disciplinary industry that includes several diverse professions and trades (Donoghue, 2004). One of the functions within mining is the operation of earth moving equipment (EME) such as haul trucks, dozers, excavators and graders. EME are generally used to shift large amounts of earth, dig foundations and landscape areas. In this study whole-body vibration (WBV) and noise exposure of earth moving equipment (EME) operators were assessed, at an opencast coalmine in South Africa. The aim was to evaluate and quantify the levels of exposure in different EME types, as well as to compare old with new EME, in order to estimate if machine hours contribute to higher noise and vibration levels. WBV and noise levels of the Production and Rehabilitation operations were compared, to determine whether different activities led to different exposures. Internationally accepted standardised methods, ISO 2631-1 for WBV and SANS 10083:2012 for noise were followed and correctly calibrated instrumentation was used. WBV measurements were conducted with a tri-axial seat pad accelerometer (SVAN 958) and personal noise dosimeters (Casella 35 X) were used for noise measurements. Measurements were taken over a period of four months. With regards to the European Union (EU) limit (1.15 m/s2) and the EU action limit (0.5 m/s2) it was noted that operators of EME within the Production operation were not exposed to WBV levels above the EU limit, but 77% of these operators were exposed to WBV levels above the EU action limit. It was also evident that 45% of operators’ vibration exposure levels were within the Health Guidance Caution Zone (HGCZ) of 0.45 – 0.90 m/s2. Within the Rehabilitation operation, 9% of operators were exposed to WBV levels above the EU limit and 55% above the EU action limit. Furthermore 50% was within the HGCZ. With regards to the noise Occupational exposure limit (OEL) of 85 dB(A) as stated by the Mine Health and Safety Regulations (MHSR) it was noted that 27% of operators within the Production operation were exposed to noise levels above the limit and for operators within the Rehabilitation operation 14% were reported to be exposed at or above the limit. Statistically significant difference in noise exposure was found between the Production operation and Rehabilitation operation. Results indicated that the majority of EME operators were exposed to high noise levels, in some cases exceeding the 85 dB(A) OEL. A significant positive correlation was found between noise exposure levels and machine hours. Thus higher noise levels were observed as machine operating hours increased. It was found that operators were exposed predominantly to vibration and noise levels below the limits. However the Dozer group within the Production and Rehabilitation operations in some cases exceeded the vibration and noise legal limit. High exposure levels within the Dozer group can be attributed to the fact that these EME types mostly perform activities in uneven areas and the tracks on which these Dozers move also contribute to higher vibration levels due to a lack of a suspension. Controls should be implemented as far as is reasonably practicable to ensure that operators are not exposed above recommended or permissible levels for each hazard. Continuous improvement of the maintenance plan for all EME and regularly grading and maintaining travelling ways are some of the controls that will contribute to lower vibration and noise levels. Operators exposed to high noise levels should use hearing protective devices as an early on preventative measure to reduce noise exposure levels. / MSc (Occupational Hygiene), North-West University, Potchefstroom Campus, 2014

Elements of an individuals occupational exposure, such as their posture can affect their comfort during work, and also their long term musculoskeletal health. Knowledge as to the extent of the influence of particular aspects of the exposures can help in providing guidance on risk evaluation, and direct future technical design focus. In many situations the exposures interact, and even if the effects of individual exposures are understood, the interactions are often less so. This is certainly the case with off-road driving exposures. Specific investigations have focussed on the effects of vibration exposure, resulting in the development of international standards and guidelines on measurement and evaluation of exposure. Consideration of the posture of the operator can be accomplished through postural assessment tools, although none of the currently available methods are developed specifically for use within a vehicle environment. The issues of both the posture of the operator and the seated vibration exposure are particularly apparent in off-road agricultural driving environments, where the driving task dictates that operator is often required to maintain specific postures whilst also exposed to whole-body vibration. In agriculture, many of the tasks require the operator to maintain axially rotated postures to complete the task effectively. The analysis of the combined effects of the axial rotation of the operator and the whole-body vibration exposure has been limited to a few studies within the literature, and is currently poorly understood. The overall aim of the thesis was to assess the influence of axial rotation and whole-body vibration on the musculoskeletal discomfort of the neck and trunk, in order that the true extent of the exposure risk may be evaluated. A field study was conducted to determine the common characteristics of some typical exposures, to provide a basis for the laboratory studies. A survey of expert opinion was conducted, examining the knowledge and experience of experts in assessing the relative influence of axial rotation and whole-body vibration on operators musculoskeletal health. The main investigations of the thesis are focussed in the laboratory, where the objective and subjective effects of axial rotation (static and dynamic) and whole-body vibration were investigated. Objective measures included the investigation of muscular fatigue in response to exposures. The tasks investigated in the field study indicated that the exposures often exceed the EU Physical Agents Exposure Limit Value, and that the axial rotation is a large component of the postures required. The survey of expert opinion concluded that combined exposure to axial rotation and whole-body vibration would increase the risks of lower back pain, and that acknowledgement of combined exposures should be included when assessing for risk. The results of the laboratory studies indicated that the greatest discomfort was present when subjects were exposed to axial rotation in the neck and shoulders. Out of the 8 muscles investigated, at most 6 of the 8 indicated fatigue during an experimental exposure. The muscle group which was affected most by the exposures was the m. trapezius pars decendens. Findings demonstrated that when subjects were exposed to axial rotation and whole-body vibration they indicated discomfort and their muscles fatigued. However, there was poor correlation between the sites of discomfort and the location of muscular fatigue. The discomfort findings suggest that there is an increased risk of discomfort from experiencing axial rotation together with whole-body vibration. Investigations of muscular fatigue do not substantiate this finding.

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Title: Influence of whole body vibration training on postural stability in selected sporting population Objectives: The aim of this study is to compare the influence of whole body vibration training on the stability of the human body and assessing the possibility of using this training method to improve postural stability in selected sporting population. Methods: 15 mainly beach volleyball players (athletes) were randomly assigned into two groups. Experimental group (n 8) in addition to their own training practiced twice a week on the Power Plate, while the control group (n 7) to continue the current practice of beach volleyball. The experimental group participated in a total of twelve units during the six-week exercise intervention. We reviewed the standard deviation and average values of COP displacements in the anteroposterior, mediolateral and overall direction of the COP path. For this purpose, we used pressure platform Footscan. Results: The results indicate a clear trend to improve postural stability at the beach volleyball player after a six-week intervention, whole body vibration training. Improvement was most noticeable in tests Flamengo (standing on one leg), in which the total COP path decreased for all probands at the right lower extremity and in six of the eight probands in the left...

Objective: Charcot-Marie-Tooth disease (CMT) is the most common hereditary motor and sensory neuropathy. Genetic mutation causes neurological disorder of peripheral nervous system. Diseases most common signs and symptoms are distal muscle weakness, foot deformities and somatosensory defect. One of the most notable consequences of the disease is balance disorder. The goal of this study was to ascertain impact of one-off application of vibration therapy on postural stability in CMT and referential group. Method: There were 16 patients diagnosed with CMT that participated in the research, 15 of which finished all procedures (average age 44.3 years, age ranges from 25 to 57 years, 12 woman and 3 men). Referential group was composed of healthy people of similar sex and age. All probands underwent measuring on Balance Master before vibration therapy, immediately after and 30 minutes later. The therapy take place in standing position in the Power Plate, therapy lasted for 5 minutes. Results: A significant improvement of Endpoint Excursion, Maximum Excursion, Movement Velocity and Sway velocity parameters was established after applying one-off vibration therapy in group of patients diagnosed with CMT. This effect endured 30 min after vibration therapy. Also we discovered that vibration therapy has stronger...

The lack of adequate equipment and measurement tools in whole-body vibration has imposed significant constraints on what can be measured and what can be investigated in the field. Most current studies are limited to single direction measurements while focusing on simple postures. Besides the limitation in measurement, most of the current biomechanical measures, such as the seat-to-head transmissibility, have discrepancies in the way they are calculated across different labs. Additionally, this field lacks an important measure to quantify the subjective discomfort of individuals, especially when sitting with different postures or in multiple-axis vibration. This work begins by explaining discrepancies in measurement techniques and uses accelerometers and motion capture to provide the basis for more accurate measurement during single- and three-dimensional human vibration responses. Building on this concept, a new data collection method is introduced using inertial sensors to measure the human response in whole-body vibration. The results indicate that measurement errors are considerably reduced by utilizing the proposed methods and that accurate measurements can be gathered in multiple-axis vibration. Next, a biomechanically driven predictive model was developed to evaluate human discomfort during single-axis sinusoidal vibration. The results indicate that the peak discomfort can be captured with the predictive model during multiple seated postures. The predictive model was then modified to examine human discomfort to whole-body vibration on a larger scale with random vibrations, multiple postures, and multiple vibration directions. The results demonstrate that the predictive measure can capture human discomfort in random vibration and during varying seated postures. Lastly, a new concept called effective seat-to-head transmissibility is introduced, which describes how to combine the human body's biodynamic response to vibration from multiple directions. This concept is further utilized to quantify the human response using many different vibration conditions and seated postures during 6D vibration. The results from this study demonstrate how complicated vibrations from multiple-input and multiple-output motions can be resolved into a single measure. The proposed effective seat-to-head transmissibility concept presents an objective tool to gain insights into the effect of posture and surrounding equipment on the biodynamic response of the operators. This thesis is timely as advances in seat design for operators are increasingly important with evolving armrests, backrests, and seat suspension systems. The utilization of comprehensive measurement techniques, a predictive discomfort model, and the concept of effective seat-to-head transmissibility, therefore, would be beneficial to the fields of seat/equipment design as well as human biomechanics studies in whole-body vibration.

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