more difficult to implement management of ergonomic controls compared to factory settings where equipment can be more easily designed to reduce postures and repetitive work exposures. He noted that, mine employees are expected to perform labour-intensive tasks that cannot be avoided due to working environmental challenges. The ever-changing status of the working environment does not allow easy implementation of mechanical assistance to reduce exposures to ergonomic hazards like repetitive work and manual handling. He observed that underground mining equipment designers generally prefer designing equipment to suit and control how the machine will function, but not the environment in which it will be used. Ergonomic risks in mining therefore cannot be eliminated by redesigning the system.
2.7 Research Gaps
Studies by Dr Seidel and colleagues: The most famous studies were carried out by Dr Seidel and colleagues who established a link between whole body vibration exposure and the incidence of lower back pain. In short, studies shed more knowledge of occupational damage and vibration exposure and the philosophy of the approach to the question of lumbar syndrome or spinal damage (Seidel 1993a, b; Seidel et al., 1980; 1986; 1995; 1997; 1998). However, the research suffers from a failure to address the non-scientific factors like the psychosocial factors.
Study of Schwarze et al: One of the most interesting studies to date has been that published by Schwarze et al., in 1997. This study covered operators of fork lift trucks, truck drivers, as well as operators of earthmoving machinery. The main limitation with this study lies not with the analysis of physiological symptoms, but with the assessment of exposure, be it to vibration or to postural stress. It would first appear that any differences in postural stress were ignored as being too difficult to differentiate, which weakens the results in comparison with those for agricultural workers by Bovenzi and Betta (1998). Clearly all exposed persons, operating whatever machine, were assumed to have similar postural loads. More importantly, the study seems to leave a knowledge gap on the complete picture.
Vancouver studies: Another recent contribution to the discussion of the mechanisms of spinal damage under shock and vibration has come from the Simon Fraser University at Vancouver (Cameron et al., 1996; Robinson et al., 1995 and Roddan et al., 1995). The team studied the dynamics of the spines of military personnel under combinations of relatively severe shock and vibration. From the publications available, it does not seem as though Morrison and Village (1989) have included posture as a contributory stress. Despite many years of research, we do not have definitive answers to the four questions implied by the objectives mentioned in chapter one.
It has not yet been shown by any study reviewed here that reducing the stress of whole-body vibration would actually reduce the incidence of lower back pain in a working population. Much of what has been presented as evidence of the effect of whole-body vibration on human health has demonstrated only the associations between certain occupations and health. In nearly all the published research, the effects of confounding factors, in particular of postural stress, have neither been quantified, nor compared with any claimed effect of vibration hence leaves one with some knowledge gaps. Very few studies of the health effects of whole-body vibration have included both cause and effect. Instead, there has been an overkill of health studies with little or no evaluation of the exposure of the subjects to dynamic stresses. The effect has been given more attention than the cause and this leaves a conceptual gap.
The few studies that have included any evaluation of exposure to dynamic stresses have two shortcomings. Firstly, exposures have been quantified as generalised vibration magnitudes measured on different machines or vehicles to those used by the actual subjects, and often averaged over a range of machines and conditions whose relationship to the subjects working conditions has not been verified. It is not therefore possible to distinguish subjects according to their vibration histories, nor to associate those subjects who have particular symptoms with their personal vibration histories. Secondly, the quantification of vibration exposure has assumed that the trade-off between magnitude and duration is already established and known. The research study described by Schwarze et al. (1997) may contain data which could be used to answer some of the above criticisms. If so, it would be useful if this could be presented in a way which allows direct comparison between groups of subjects who were exposed to high magnitude vibration for short daily periods with others who were exposed to lower magnitudes of vibration for long daily exposures. The fact that this has not been done gives a reason for a research that can fill in this gap so that a complete picture is created.
2.8 Theoretical Framework
The theoretical framework of this study identifies with the theory that the cause of lower back pain in LHD drivers is multifaceted and may be influenced by a host of factors in the work environment, such as type of work process and machinery, work postures, heavy lifting and biodynamic factors, as well as various individual characteristics and stress (Hagberg et al., 2006; Palmer et al., 2003; Hoy et al., 2005 and Hoogendoorn et al., 1999). The broader theoretical approaches view lower back pain incidences as being epidemiological (epidemiological theory), scientifically measurable (scientific theory) and a public health issue. Most lower back pain research in primary care falls within the (clinical) epidemiologic theory and the main objective is, directly or indirectly, to promote more effective and efficient behaviour in patients and health care professionals. Epidemiologic studies however focus on the causal relation between the occurrence of lower back pain (as the dependent variable) and other determinants (as independent variables) such as, diagnostic, or prognostic factors, including therapy (clinical theory).
The preferred theory proposed by this study is the multivariate interaction theory of musculoskeletal injury precipitation. In this theory, interactions between genetic, morphological, psychosocial and biomechanical factors impact on the individuals’ lower back. The impact could result in strain, structural and or biochemical changes and eventually pain. The exposures in this theory are biomechanical factors, the doses are the impacts on the musculoskeletal system, the response is the strain in the form of structural, biochemical or physiological changes and capacity affected
2.9 Conceptual Framework
The conceptual framework developed from the literature review outlines risk factors associated with lower back pain amongst LHD drivers. The risk factors have been classified into six categories: demographic, organisational, work related, economical, biomechanical and psychosocial. Demographic factors consist of variables such as age, sex, education, sensitivity to pain, obesity or weight gain, history of back pain or injury and physical activity. Work related factors include road condition, equipment conditions and equipment design. Economic factors are income. Organisational factors include environmental factors, structure of shift (job design), command structure and workload. Psychosocial factors comprise depression, passive pain, occupation and alcohol and or drug abuse. Biomechanical factors include movement and or coordination and increased workload. Thus, lower back pain is due multifactorial causes.