Low-back disorders (LBDs) are the leading cause of lost work days and the most costly occupational safety and health problem facing industry today. The nature of industrial MMH has been rapidly changing from lifting to push-pull exertions. Epidemiological studies identify pushing and pulling as a major LBD risk factor, i.e. 20% of injuries. Unfortunately, little is known regarding biomechanics risks of industrial pushing tasksBiomechanical risk of LBD includes components of spinal load, spinal stability and material tolerances such as disc and vertebral fracture limits. Preliminary calculations suggest spinal stability is severely limited during pushing exertions thereby requiring increased muscle co-contraction. Co-contraction is known to increase spinal loads. Moreover, push forces are expected to introduce increased risk from spinal shear forces. Few published studies have examined spinal load during pushing exertions, NONE have considered the influence of coactivation, few have considered shear load and NONE have considered spinal stability. The goal of this effort is to quantify the biomechanical risk factors imposed by pushing tasksWe will perform a multi-institutional biomechanical analyses of pushing exertions including in-vivo assessment of spinal compression, spinal shear force and spinal stability.
In Specific Aim #1 we will calibrate the EMG-assisted model of spinal load to permit analysis of pushing exertions. Preliminary data indicate large increases in trunk muscle co-contraction during pushing versus lifting tasks. This model accounts for trunk muscle co-contraction in the determination of spinal load and permits estimation of spinal shear force. The calibration and validation procedure will include experimental comparison of trunk flexion versus extension exertions. Increased co-contraction indicates the pushing tasks are associated with reduced spinal stability.
In Specific Aim #2 we will calibrate and further develop the spinal stability model to permit analyses of pushing exertions including assessment of dynamic stability. This process will include experimental measurement of trunk kinematics, kinetics and EMG following sudden perturbations in both flexion and extension moment conditions.
In Specific Aim #3 we will evaluate the influence of workplace factors on spinal compression, shear force and stability. Experimental will record the influence of push force and handle height on spine biomechanics. In a second experiment we will examine how handle stability influences biomechanical risk. A third experiment will evaluate the influence of exertion dynamics on biomechanical risk, i.e. the influence of the inertial mass of the pushed object, the velocity of movement, and compare the spinal loads and stability of pushing a cart versus pushing an overhead lift-assist device.
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