The role of complex, simultaneous trunk motions in the risk of occupation-related low back disorders.

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Simultaneous trunk kinematic variables of industrial workers performing jobs with varying degrees of low back disorder risk were quantified, by using a three-dimensional electrogoniometer. To assess the distinguishing patterns of simultaneous multidimensional (complex) motion parameters of workers performing manual material handling jobs with varying degrees of low back disorder risk. There is significant epidemiologic and biomechanical evidence that implicates simultaneously occurring or combined motions and loading as important risk factors follow back disorder. However, the specific levels or magnitudes and patterns of these complex motions at which risk of low back disorder is increased are still unknown. An industrial database of 126 workers and jobs was used to quantify the complex trunk motions of groups with varying degrees of low back disorder risk. Three groups, low-, medium-, and high-risk, were defined on the basis of retrospective injury records of the corresponding jobs. The jobs were further classified into five cells of weight-lift rate combinations. Within each weight-lift rate cell, the three-dimensional trunk motion patterns of workers were analyzed. Bivariate distributions and cumulative distribution functions were used to compare the simultaneous occurrence of complex dynamic motions among risk groups. High- and medium-risk groups exhibited complex trunk motion patterns involving high magnitudes of combined velocities, especially at extreme sagittal flexion; whereas the low-risk group did not. Postural trunk information alone did not provide a consistent pattern of distinguishing among risk groups. Elevated levels of complex simultaneous velocity patterns were unique to groups with increased low back disorder risk. Knowledge of these complex trunk velocity patterns in combination with key workplace factors provides a more sensitive means for identifying low back disorder occupational risk factors than does mere postural information.