Documents Marras, William S. 8 results

"This article provides a review of the biomechanics literature on the low back and upper extremities. Biomechanics is the study of forces acting on and generated within the body and of the effects of these forces on the tissues, fluids, or materials used for diagnosis, treatment, or research purposes. The discussion begins with an overview of basic concepts and methods. This is followed by the two literature reviews. The study selection criteria are presented at the beginning of each review. The two bodies of literature differ in maturity; the research on the low back is more substantial. The number of studies reviewed is 196 for the low back and 109 for the upper extremities. While there are certainly individual factors that put a person at risk for back pain, overall, this body of literature indicates that back pain can be related to excessive mechanical loading of the spine that can be expected in the workplace. The literature also indicates that appropriate reduction of work exposure can decrease the risk of low back disorder. Hence, it is clear, from a biomechanical perspective, that exposure to excessive amounts of physical loading can increase the risk of low back disorder."

This study evaluated spinal loads associated with lifting and hanging heavy mining cable in a variety of postures. This electrical cable can weigh up to 10 kg per metre and is often lifted in restricted spaces in underground coal mines. Seven male subjects performed eight cable lifting and hanging tasks, while trunk kinematic data and trunk muscle electromyograms (EMGs) were obtained. The eight tasks were combinations of four postures (standing, stooping, kneeling on one knee, or kneeling on both knees) and two levels of cable load (0 N or 100 N load added to the existing cable weight). An EMG-assisted model was used to calculate forces and moments acting on the lumbar spine. A two-way split-plot ANOVA showed that increased load (p < 0.05) and changes in lifting posture (p < 0.05) independently affected trunk muscle recruitment and spinal loading. The increase in cable load resulted in higher EMG activity of all trunk muscles and increased axial and lateral bending moments on the spine (p < 0.05). Changes in posture caused more selective adjustments in muscle recruitment and affected the sagittal plane moment (p < 0.05). Despite the more selective nature of trunk EMG changes due to posture, the magnitude of changes in spinal loading was often quite dramatic. However, average compression values exceeded 3400 N for all cable lifting tasks.

The aim was to identify which biomechanical and physiological variables were associated with the decision to change the weight of lift during the determination of the maximum acceptable weight of lift (MAWL) in a psychophysical study. Fifteen male college students lifted a box of unknown weight at 4.3 lifts/min, and adjusted the weight until their MAWL was reached. Variables such as heart rate, trunk positions, velocities and accelerations were measured during the lifting, as well as estimated spinal loading in terms of moments and spinal forces in three dimensions using an EMG-assisted biomechanical model. Multiple logistic regression techniques identified variables associated with the decision to change the weights up and down prior to a subsequent lift. Results indicated that heart rate, predicted sagittal lift moment and low back disorder (LBD) risk index were associated with decreases in the weight prior to the next lift. Thus, historical measures of LBD risk (e.g. compression, shear force) were not associated with decreases in weight prior to the next lift. Additionally, the magnitudes of the predicted spinal forces and LBD risk were all very high at the MAWL when compared with literature sources of tolerance as well as observational studies on LBD risk. Our findings indicate that the psychophysical methodology may be useful for the decision to lower the weight of loads that may present extreme levels of risk of LBD; however, the psychophysical methodology does not seem to help in the decision to stop changing the weight at a safe load weight.

"Spinal compression is traditionally assumed the principal biomechanical mechanism associated with occupationally related low-back disorders (LBD). However, there is little conclusive evidence demonstrating that compression is related to occupational LBD. The objective of this research was to examine whether axial compression in the lumbar spine can predict the probability that a lifting task should be classified as high risk for LBD. Furthermore, the improvement in predictive ability was examined when analyses include 3-D, dynamic biomechanical factors. Ten experienced warehouse workers transferred 12 pallet loads of boxes in a simulation of warehouse working conditions. Biomechanical estimates of 2-D static and 3-D dynamic spinal compression, shear loads and tissue strains were achieved from the subjects during each lifting exertion. Each lift was also assessed for probability of high LBD risk classification. Regression analyses were performed to examine the relationship between biomechanical and epidemiological factors. Results indicate 2-D static estimates of spinal compression describe ~ 13% of the probability of high LBD risk variability. Dynamic estimates of spinal compression describe >44% of the variability. A multifactor regression model including 3-D spinal loads and tissue strains further improved the predictive ability, but the improvement was not statistically significant. This research demonstrates the biomechanical source of low-back pain is dynamic, multifaceted and multidimensional. Significant improvements in ergonomics assessments can be achieved by examining interactions of dynamic biomechanical factors. Unfortunately, this improved predictive ability is generated at the high cost of computational complexity. However, less realistic biomechanical representations may ignore the injury mechanisms associated with the greater number of workplace injuries. Thus, improved understanding of the dynamic biomechanical interactions influencing the tolerance and injury mechanisms of the spine may permit more accurate assessments of workplace injury factors associated with LBD and reduced incidence of occupationally related low-back pain. "

"Although patient handlers suffer from low-back injuries at an alarming rate worldwide, there has been limited research quantifying the risk for the specific tasks performed by the patient handlers. The current study used both a comprehensive evaluation system (low-back disorder risk model) and theoretical model (biomechanical spinal loading model) to evaluate risk of LBD of 17 participants (12 experienced and five inexperienced) performing several patient handling tasks. Eight of the participants were female and nine were male. Several patient transfers were evaluated as well as repositioning of the patient in bed; these were performed with one and two people. The patient transfers were between bed and wheelchair (fixed and removable arms) and between commode chair and hospital chair. A 'standard' patient (a 50 kg co-operative female; nonweight bearing but had use of upper body) was used in all patient handling tasks. Overall, patient handling was found to be an extremely hazardous job that had substantial risk of causing a low-back injury whether with one or two patient handlers. The greatest risk was associated with the one-person transferring techniques with the actual task being performed having a limited effect. The repositioning techniques were found to have significant risk of LBD associated with them with the single hook method having the highest LBD risk and spinal loads that exceeded the tolerance limits (worst patient handling job). The twoperson draw sheet repositioning technique had the lowest LBD risk and spinal loads but still had relatively high spinal loads and LBD risk. Thus, even the safest of tasks (of the tasks evaluated in this study) had significant risk. Additionally, the current study represented a 'best' case scenario since the patient was relatively light and co-operative. Thus, patient handling in real situations such as in a nursing home, would be expected to be worse. Therefore, to have an impact on LBD, it is necessary to provide mechanical lift assist devices. "

"Pushing and pulling tasks using carts and material handling devices have become more prevalent in occupational environments in an attempt to reduce the musculoskeletal risks associated with lifting. However, little change in low back disorder rates have been noted as tasks change from lifting to pushing and pulling indicating that we do not understand the mechanics of pushing and pulling well. Biomechanical assessments of pushing and pulling tasks using person-specific biologically assisted models offer a means to help understand how the spine is loaded under pushing and pulling conditions. However, critical components of these models must be adjusted so that they are sensitive to the different physiologic responses in the torso muscles expected during pushing and pulling compared to lifting tasks.The objective of this study was to modify an electromyography (EMG)-assisted biomechanical model designed to evaluate lifting tasks so that it can better represent the biomechanical forces expected during pushing and pulling tasks. Several key modifications were made. Based upon a literature review, changes in muscle cross-sectional area and muscle origins and insertions were made to better represent the geometry of the torso muscles. It was also necessary to adjust the length-force and velocity-force muscle relationships. Empirically derived length-force and velocity-force relationships were developed to independently represent the flexor and extensor musculature. These modifications were then systematically incorporated into the model.The model was exercised over several pushing and pulling conditions to assess the effect of these modifications on its ability to predict externally measured spinal moments. Results indicated that the alterations made to the preexisting EMG-assisted model resulted in acceptable model performance for pushing, pulling, and lifting activities.Relevance to industryThe use of carts and material handling devices has become increasingly prevalent in industry, though little research has been done to examine the body's response. The modifications made to the biomechanical model would enable its use in the evaluation and design of material handling devices and pushing and pulling tasks."

"Among other purposes, companies and regulatory agencies from around the world often adopt International Standard Organization (ISO) standards to determine acceptable practices, equipment and criteria for preventing occupational injuries and illnesses. ISO standards are based on a consensus among individuals who participate in the process. This discussion paper examines the scientific process for the development of several ISO standards on biomechanical factors, comparing it with processes used by other professional organizations, including scientific committees working on the development of clinical guidelines. While the ISO process has value, it also has clear limitations when it comes to developing occupational health and safety standards that should be based on scientific principles."