Musculoskeletal loading of seated occupational drivers exposed to whole-body vibration; vibration control

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Operators of heavy road and off-road vehicles, employed in various work sectors, are constantly exposed to high magnitudes of low frequency vibration of whole-body nature, while they are required to sit within confined space over long durations. Both, the prolonged sitting in a confined space and exposure to whole-body vibration (WBV) are believed to be the major sources of spinal stresses leading to low back pain (LBP). Many epidemiologic and laboratory studies have established strong associations between LBP among occupational drivers and exposure to WBV. An EC study has estimated that 4 to 7% of all employees in the USA, Canada and some European Countries are exposed to potentially harmful WBV, while others have estimated the associated annual compensation and medical costs in the order of several billion dollars. Although a generally accepted relationship between WBV exposure and LBP does not yet exist, it is hypothesized that prevention of injury risks requires design of suspension seats that provide enhanced isolation of vibration and shock, and postural support conditions. The primary objective of this study is to investigate an adaptively controlled occupant seat comprising a magneto-rheological fluid based suspension to attenuate the injurious WBV transmitted to the occupant, and a flexible and adaptive support surface to provide desirable support conditions that would reduce the spine loads. The assessment of spine loads as functions of the sitting and vibration environment, and support conditions will be attempted through different measures in terms of transmitted vibration, distribution of body-seat interface forces, relative compression and extension of the column, activities of erector spinae muscles using surface EMG, and biodynamic and transfer-impedance responses. The results would allow for identification of most desirable support conditions that could reduce the transmitted vibration, concentration of body-seat forces, and spine loads as measured from the biodynamic and physiological factors.