2.1 Lower Back Pain

Yilmaz and Dedeli (2012) define lower back pain as pain associated with muscle tension, or stiffness localised below the costal margins and above the inferior gluteal folds, with or without leg pain. Further they observe that muscular strain, facet joint arthritis, or disc pressure on the annulus fibrosis, vertebral end-plates or nerve roots are conditions which cause lower back pain. Lower back pain is ranked as the most widespread musculoskeletal condition and the highest common cause of disability in developed nations (Woolf and Pfleger, 2003). Dias (2014) notes that a back disorder involves a range of conditions which range from acute onset with a short duration to chronic conditions which include osteoarthritis, disc degradation, osteoporosis and common lower back pain. Musculoskeletal pain, especially lower back pain is seen as one of the most common occupational health problems and accounts for large numbers of man lost days and disability in most countries.

Dias (2014) also observes that, ligament strain, facet joint arthritis or disc pressure on the annulus fibrosis vertebral-end place or nerve roots are conditions which cause lower back pain. For Yilmaz and Dedeli (2012), incidents of lower back pain are simply associated with manual material handling task parameters and the risk of lower back pain injury may be completely as a result of the design of the workplace or as a result of workplace factors. They argue that, lower back pain is a condition characterised by stages ranging from acute to chronic. A chronic condition is when an individual has a back pain that persists for more than twelve weeks continuously, whereas an acute condition is when one has a back pain for less than twelve weeks and it has stopped or becomes intermittent. The dominant theory of causation supported by this study is one that states that the exposure to whole body vibration is the leading cause of lower back pain in LHD drivers. Whole body vibration is said to occur when a body is supported on a vibrating surface, usually a seat or a platform. WBV is an oscillation with frequency ranging from 0.01 to 50 Hertz which is transmitted to the human body and can result in motion sickness, discomfort, pain, vomiting and numbness to the skin, Uchikune (2004). Vibration exposure to the human body is not simple, as the human body is exposed to various frequencies in different directions (Griffin, 1990).

When vibration occurs, the body is exposed to physiological and pathological effects (Griffin et al., 1990). Whole body vibration exposure is said to cause a vascular change (which enables the passage of respiratory gases, nutrients, excretory products, and other metabolites into and out of the cells) resulting in nutritional compromise of the tissues around the spine. It is noted that these changes result in muscle fatigue and compression of the discs (Magnusson et al., 1998). Wilder (1993) notes that sitting in a vibrating environment can lead to an additional rocking of the pelvis rotation which may amplify the vibration transmitted to the spine, and may also increase the rate of disc degeneration (which is normally observed through the height of the spinal disc reducing gradually).

Seidel (1993) pointed out that WBV exposure is defined as the vibration measured at the interfaces between the machine and the operator, that is mainly at the driver seat. The spinal health risk arises from a mechanical damage of anatomical structures due to forces (internal load) acting on these anatomical structures. On the other hand, Waters et al (2005) suggested that drivers of underground vehicles suffer musculoskeletal disorders due to various occupational risk factors. The list of factors includes static sedentary positions while driving (hands and feet held steady on handles and pedals), repeated exposure to short and long term awkward trunk posture especially during reverse operation and exposure to whole body vibration while vehicle is in motion.

2.2 Work related ergonomic factors
Donoghue (2004) defines an ergonomic risk as a physical factor within the workplace environment that harms the musculoskeletal system. He observed further that ergonomic hazards involve repetitive movements, manual handling, workplace or job task design, uncomfortable workstation height and poor body positioning. For the mining industry these hazards are responsible for the cause of occupational back disorders where they are dominant. Bach and Orhede (1995) observed that ergonomic factors can include the physical set up of workspaces, working environment, tools, vehicles, and structures. Ergonomic associated factors are reported by several studies to be major contributors of occupational lower back pain among mining workers. Karra (2005) conducted a study in Ghana which noted that, frequent gestures, powerful efforts, vibration exposure, poor or awkward postures, forceful gripping and jolting or jarring are ergonomic risk factors responsible for occupational lower back pain among Ghana mine workers.

Kunda et al. (2013) in Zambia concluded in a study that there are eight different ergonomic hazards which mine workers are reported to be exposed to. They identified heavy lifting, awkward postures, high hand force, highly repetitive work, vibrating tools, bouncing or jarring, static postures (sitting or standing) and pushing and pulling as some of the factors. Torma et al (2007) who carried out a study in China declared that a high prevalence of back pain in mining is due to ergonomic associated factors like manual lifting, awkward postures, powerful gripping, pushing and pulling and high repetitive work while the least reported prevalence and exposures to lower back pain cases was associated with bouncing and jarring.

The World Health Organization (2002), recorded that occupational lower back injuries occur frequently in industrialised countries, for example in America where half of working people are reported to be suffering from occupational back pain every year. Guangxing et al., (2012) who conducted a study in China noted that underground workers carry out a number of tasks which include heavy lifting, bending, prolonged standing, and working in confined spaces, unlike surface workers who are more into transporting, servicing, and repairing equipment. The National Institute for Occupational Safety and Health (NIOSH), concluded for American mine workers, there is a causal relationship between LBP and manual lifting.

2.3. Previous studies on prevalence of lower back pain.
A study in South Africa concluded that, lower back pain was responsible for 27% of all occupational diseases from 1990 to 2000, Vuuren (2006). Deyo et al., (2006) researching in America found that about 25% of adults in the United States of America were reported to have suffered from lower back pain before and that the incidence generally responded with greater levels of education and an increase in income. Kent and Keating (2005) from an American study concluded that 42.6% of the study population was experiencing occupational lower back pain with 10.5% experiencing high activity limitations.

Torril et al (2003) in preceding studies in Britain concluded that, 49% of lower back disorder prevalence was reported over one year and a 35 % prevalence was reported over one month in the Nordic countries. In Norway, a study revealed that 25% of the total working class suffered from lower back pain of which 15% of the total sick leave in 1999 was attributed to occupational lower back pain, Badley (2005). Studies conducted in Canada, Finland and the United States of America recorded that most disability is as a result of musculoskeletal disorders (MSDs), (Badley 2005). Duthey (2014) carried out a study in United Kingdom and concluded that lower back problems were the most common cause of disability in working adult population with more than 100 million work days lost per year in the mining industry. In America, it is estimated that 149 million days of work per year are lost due to LBP. The burden of LBP is clearly costly, with total cost estimates topping US$ 200 billion annually, Duthey (2014).

2.4 Occupational risk factors and lower back pain
Latza et al (2002) in Germany highlighted that work place situations listed as awkward postures for long hours contribute to the occurrence of lower back pain disorders. Jones and Kumar (2001) in a comparative study in America between mining and construction environments concluded that, the mining industry has many workplace factors that predispose manual workers to lower back pain. They noted that activities undertaken by manual mine workers are mostly highly mechanical thereby causing them to suffer more from back pain than manual construction workers as compared to technical workers (Jones and Kumar, 2001).

Vibration which can be either segmental or whole body is another occupational factor which manual workers and truck drivers or operators in mining are exposed to due to the nature of their work (Punnett et al, 2005). Archer (2010) observed that vibration on the musculoskeletal system of the body causes deterioration of the small cartilage (intervertebral) discs, allowing tissues and nerves to be strained and pinched leading to various lower back problems. The longer a person is exposed and the higher the level of whole body vibration, the greater the chances of suffering from a back injury

Literature therefore shows that the operation of mining machines like LHD machines, heavy lifting, and forceful exertions are factors identified to be the major causes of lower back pain among mining employees across the world. This study also reported that inadequate healing time is another factor (Punnett et al, 2005). It is submitted that can lead to repeated trauma on the lumbar spine and hence cause employees to feel lower back pain. Mital (1997) added that turning and twisting are ergonomic factors which affect the spine due to the nature of the anatomical structure of the annulus fibrous which contains the disc. Karra (2005) summarises that ergonomic factors as the major cause of musculoskeletal injuries in mines and the factors identified are repetitive motions, forceful exertions, vibration exposures and poor or awkward working postures. Krajewski (2007) also points out that tedious awkward body positions resulting from excessive bending (forward and lateral) and twisting (trunk rotation or torsion) increase spinal stress and loading to spinal structures.

2.5 Work related activities and postures identified by studies to cause lower back pain.
Pushing and Pulling: Magora (2017) noted an increased LBP in those employees whose occupations required them to do pushing and pulling most of the time. Ayoub and McDaniel (1999) suggest that the type of posture adopted most of the time while doing work is a critical determinant in the force capability in both pushing and pulling. In America LBP injuries were observed to be more prevalent amongst American mining employees who work underground where ore is pushed in rail trolleys from one level to another level, NIOSH (2013).

Lifting: Pope (2002) narrows the point to that of LBP being mostly linked to poor lifting practices. Brinkman et al (1998) highlighted that, the principle of lifting is determined by how one holds the object being lifted as near to the body as possible, which is more important than keeping a straight back. He further noted that spinal loading increases during forward bent posture and this results in a height decrease or deformation of lumbar vertebrae.

Postures: The exact science of harmful postures has not been conclusive. Pope (2002) seems to conclude that, postures mostly adopted by workers like bending, contribute about 90% of lower back pain incidents. Frequent bending results in back disorders as it enables the spine to fully bend, thereby changing the line of action of the largest extensor muscles. Employees who work in extreme postures for example, kneeling and bending postures which were identified by Gallagher et al (1994) are said to be affected most by lower back pain, especially among construction and mining workers.

Standing posture: These have been reported by several researchers to cause lower back pain especially in the mining environment where employees work long hours in a standing posture. Pope et al (2002) concluded that there is a positive relationship between prolonged standing and LBP. It was also noted that, awkward postures are also responsible for causing lower back pain among mining workers. They further state that high levels of muscle activity and twisting were found to have a strong relationship with occupational LBP. Previous studies concluded that, loading and awkward postures occur from slipping, tripping, and falling events ranging from 36% to 70% due to LBP injuries (Pope et al., 2002). Bovenzi and Hulshof (1998) found a positive relationship between LBP and WBV. Schwarze et al (1998) concluded that, it is certain that LBP is increased by exposure to WBV especially for operators of rigid machines like LHD trucks. Fritz (1999) conducted a study among earthmoving machine operators and introduced the age factor that concludes that the risk from exposure to WBV increases with the age of the operator.

Sitting posture: Identified by Magora (1974) as the major cause of LBP especially among LHD drivers with jobs which allow them to sit for long periods of time due to long shifts. An increase in symptoms of LBP was discovered in employees who sit for extended periods. Increased sitting occurs due to increased trunk moment when the pelvis rotates backward and disc twist caused by the lumbar spine ?attening. It is observed that seated posture depends on seat design, sitting habits, the task, seat height and inclination, back rest position, shape and inclination, (Gallagher et al., 1994).

2.6 Mining ergonomic issues
Donoghue (2004) concluded that the mining industry has increasingly become more mechanised even though there is a substantial amount of manual handling. Prolonged disabilities found in mining carry on to institute the largest category of occupational diseases which result to trauma disorders. He further observed that in mining, overhead work which is mostly done during ground support or face barring and during the suspension of pipes and electrical cables can cause or worsen shoulder and lower back disorders. Cornelius (1993) articulates that the mining environment is