Fadi A. Fathallah

The role of dynamic three-dimensional trunk motion in occupationally-related low back disorders : the effects of workplace factors, trunk position, and trunk motion characteristics on risk of injury

Current ergonomic techniques for controlling the risk of occupationally-related low back disorder consist of static assessments of spinal loading during lifting activities. This may be problematic because several biomechanical models and epidemiologic studies suggest that the dynamic characteristics of a lift increase spine loading and the risk of occupational low back disorder. It has been difficult to include this motion information in workplace assessments because the speed at which trunk motion becomes dangerous has not been determined. An in vivo study was performed to assess the contribution of three-dimensional dynamic trunk motions to the risk of low back disorder during occupational lifting in industry. More than 400 repetitive industrial lifting jobs were studied in 48 varied industries. Existing medical and injury records in these industries were examined so that specific jobs historically categorized as either high-risk or low-risk for reported occupationally-related low back disorder could be identified. A triaxial electrogoniometer was worn by workers and documented the three-dimensional angular position, velocity, and acceleration characteristics of the lumbar spine while workers lifted in these high-risk or low-risk jobs. Workplace and individual characteristics were also documented for each of the repetitive lifting tasks. A multiple logistic regression model was developed, based on biomechanical plausibility, and indicated that a combination of five trunk motion and workplace factors distinguished between high and low risk of occupationally-related low back disorder risk well (odds ratio: 10.7). These factors included 1)lifting frequency, 2) load moment, 3) trunk lateral velocity, 4) trunk twisting velocity, and 5) the trunk sagittal angle. This analysis implies that by suitably varying these five factors observed during the lift collectively, the odds of high-risk group membership may decrease by almost 11 times. The predictive power of this model was found to be more than three times greater than that of current lifting guidelines. This study though not proving causality, indicates an association between the biomechanical factors and low back disorder risk. This model could be used as a quantitative, objective measure to design the workplace so that the risk of occupationally-related low back disorder is minimized.

Biomechanical risk factors for occupationally related low back disorders

A continuing challenge for ergonomists has been to determine quantitatively the types of trunk motion and how much trunk motion contributes to the risk of occupationally-related low back disorder (LBD). It has been difficult to include this motion information in workplace assessments since the speed at which trunk motion becomes dangerous has not been determined. An in vivo study was performed to assess the contribution of three-dimensional dynamic trunk motions to the risk of LBD during occupational lifting in industry. Over 400 industrial lifting jobs were studied in 48 varied industries. The medical records in these industries were examined so that specific jobs historically categorized as either low, medium, or high risk for occupationally-related LBD could be identified. A tri-axial electrogoniometer was worn by workers and documented the three-dimensional angular position, velocity, and acceleration characteristics of the lumbar spine while workers worked at these low, medium, or high risk jobs. Workplace and individual characteristics were also documented for each of the repetitive lifting tasks. A multiple logistic regression model indicated that a combination of five trunk motion and workplace factors predicted well both medium risk and high risk occupational-related LBD. These factors included lifting frequency, load moment, trunk lateral velocity, trunk twisting velocity, and trunk sagittal angle. Increases in the magnitude of these factors significantly increased the risk of LBD. The analyses have enabled us to determine the LBD risk associated with combined changes in the magnitudes of the five factors. The results indicate that by suitably varying these five factors observed during the lift collectively, the odds of high risk group membership may decrease by over ten times. These results were related to the biomechanical, ergonomic, and epidemiologic literature. The five trunk motion and workplace factors could be used as quantitative, objective measures to redesign the workplace so that the risk of occupationally-related LBD is minimized.

Accuracy of a three-dimensional lumbar motion monitor for recording dynamic trunk motion characteristics

There has been an abundance of evidence in the past decade that indicates that the asymmetric positioning as well as the dynamic action of the trunk during work greatly affects the ability of a worker to perform a lifting task. This is true because trunk strength decreases as the trunk moves more asymmetrically and more rapidly. Loading of the spine is also believed to increase under these conditions, since significantly greater trunk muscle activity has been observed under these conditions. Therefore, we must begin to document the asymmetric positions as well as the dynamic motion characteristics of the trunk when workers are exposed to various work tasks. This paper describes a lumbar motion monitor (LMM) that has been developed for this purpose. The LMM is an exoskeleton of the spine that is instrumented so that instantaneous changes in trunk position, velocity and acceleration can be obtained in three-dimensional space. The current study has assessed the accuracy and reliability of the LMM to measure such motion components. The results of this analysis indicate that the LMM is extremely reliable and very accurate. This study has shown that the LMM is about twice as accurate as a video-based motion evaluation system. The benefits and implications of using an LMM for work assessment and clinical use are discussed.

Musculoskeletal disorders in labor-intensive agriculture

This paper gives an overview of the extent of musculoskeletal disorders (MSDs) in agriculture, and a historical perspective on how ergonomics has been used to reduce the health effects of labor-intensive agriculture. A summary of exposure to MSD physical risk factors within various classes of crops, along with various administrative and engineering controls for abating MSDs in agriculture is given. These controls range from programmed rest breaks to mechanized or partially-mechanized operations. Worker-based approaches such as prone carts and platforms, and load transfer devices hold promise in combating the prevalent stooped work in agriculture. Including the worker as an integral contributor to all aspects of developing and implementing an intervention, and considering the psychosocial and socio-cultural aspects of the work environment are crucial elements of effective interventions for reducing MSDs. Despite the advent progress in new technologies in agricultural practices, reliance on labor, especially in fresh market fruits and vegetables, will always be a major cornerstone of agriculture for at least the foreseen future. It is encouraging to see the increased interest among health and safety professionals, epidemiologists, engineers, social scientists, and ergonomists throughout the world who are committed to the plight of reducing MSDs and other health problems among agricultural workers.

An assessment of complex spinal loads during dynamic lifting tasks.

Study Design. An electromyogram‐assisted free‐dynamic lifting model was used to quantify the patterns of complex spinal loads in subjects performing various lifting tasks. Objectives. To assess in vivo the three‐dimensional complex spinal loading patterns associated with high and low risk lifting conditions that matched those observed in industrial settings. Summary of Background Data. Combined loading on the spine has been implicated as a major risk factor in occupational low back disorders. However, there is a void in the literature regarding the role of these simultaneously occurring complex spinal loads during manual lifting. Methods. Eleven male subjects performed symmetric and asymmetric lifting tasks with varying speed and weight. Reactive forces and moments at L5‐S1 were determined through the use of electrogoniometers and a force plate. An electromyogram‐assisted model provided the continuous patterns of three‐dimensional spinal loads under these complex lifting tasks. Results. The results showed that complex dynamic motions similar to those observed in risky industrial tasks generated substantial levels of combined compressive and shear loads. In addition, higher loading rates were observed under these conditions. Unlike loading magnitudes, loading rate was a better indicator of dynamic loading because it incorporated both the duration and magnitude of net muscle forces contributing to total spinal loading during the lifting conditions. Conclusions. Quantification of spinal combined motions and loading in vivo has not been undertaken. This study provided a unified assessment of the effects of combined or coupled motions and moments in the internal loading of the spine. Dynamic lifting conditions similar to those observed in risky industrial situations generated unique complex patterns of spinal loading, which have been implicated to pose a higher risk to the spinal structure. The higher predicted loading and loading rate during asymmetric lifting conditions can be avoided by appropriate ergonomic workplace modifications.

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

Study Design. 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. Objectives. 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. Summary of Background Data. There is significant epidemiologic and biomechanical evidence that implicates simultaneously occurring or combined motions and loading as important risk factors for low 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. Methods. 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. Results. 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 for distinguishing among risk groups. Conclusions. 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.

Challenges in assessing risk factors in epidemiologic studies on back disorders

In epidemiologic studies on musculoskeletal disorders, some risk factors, especially physical load, cannot be determined independently from the worker. Posture, movement and external load are the result both of physical work requirements forced on the worker and of the workers capacity to adopt particular techniques. Risk factors are also adjusted in relation to the workers health. This paper presents a dynamic model that links exposure to risk factors for back pain and disability. Its aim is to help identify core elements in exposure assessment strategies for epidemiologic studies on back disorders. In this dynamic model, risk factors are determined relative to health status in order to distinguish between etiological and prognostic factors. Measurement techniques for various risk factors are classified into self-reports, observations, and direct instrumentation. Features of commonly used techniques are discussed with respect to feasibility, accuracy, and precision. In addition, consideration is given to the optimum allocation of measurements taking into account the effects of random and systematic variation in exposure due to tasks, workplaces, and workers.

A method for measuring external loads during dynamic lifting exertions

Biomechanical analyses of lifting exertions often require measured values of applied trunk moments and forces as baseline or validation data. Accurate measures of the trunk kinetic data are difficult to achieve from dynamic exertions without significant approximation, cost, or motion constraints. The purpose of this effort was to develop and validate a means to directly measure multi-dimensional, trunk moments which occur during dynamic lifting exertions. Force plate reaction loads coupled through a lower-body isolation structure designed to fasten the hips and legs into a known static position, were employed to compute the moment vectors about the lumbar spine. Results demonstrate the applied moments about the lumbo-sacral junction of the spine can be accurately measured from a single force plate, allowing biomechanical evaluation of dynamic lifting exertions without constraining the motions of the upper body.

Timing of Activation of the Erector Spinae and Hamstrings During a Trunk Flexion and Extension Task

Study Design Timing of activation of the hamstrings and erector spinae was assessed using surface electromyography. Objectives To investigate the influence of posture and movement speed during trunk flexion–extension on the flexion–relaxation response and trunk muscle activation patterns. Summary of Background Data The literature contains numerous reports on coactivity and synergistic behavior of major muscle groups during trunk flexion–extension. There are few reports on the timing of muscle activation. Methods Six subjects were recruited for a training session and six biweekly test sessions. Ten surface electromyogram electrodes and a lordosimeter were used to record timing of lumbar motion and muscle recruitment in the hamstrings and at four sites in the thoracolumbar region. A 3 × 2 within-subject factorial design was used to test the effects of posture and speed on activation patterns. Results Patterns of muscle activation were found to be dependent on posture and the direction of movement. The flexion–relaxation response was pervasive in the lumbar region but was less consistent at the T9 and hamstring sites. Significant differences in the delay between electromyogram activation and lumbar motion were found for the standing postures at initiation of extension, in which activation progressed in the caudad-to-cephalad direction. Conclusions The flexion–relaxation response is ubiquitous in the lumbar erector spinae and is present in the hamstrings and lower thoracic erector spinae, although not consistently in all subjects. In standing, timing of activation differed significantly by site in extension but not in flexion. Muscle activation patterns and flexion–relaxation were consistent over six biweekly test sessions.

MAXIMUM FORCES SUSTAINED DURING VARIOUS METHODS OF EXITING COMMERCIAL TRACTORS, TRAILERS AND TRUCKS

Many commercial vehicles have steps and grab-rails to assist the driver in safely entering/exiting the vehicle. However, many drivers do not use these aids. The purpose of this study was to compare impact forces experienced during various exit methods from commercial equipment. The study investigated impact forces of ten male subjects while exiting two tractors, a step-van, a box-trailer, and a cube-van. The results showed that exiting from cab-level or trailer-level resulted in impact forces as high as 12 times the subjects body weight; whereas, fully utilizing the steps and grab-rails resulted in impact forces less than two times body weight. An approach that emphasizes optimal design of entry/exit aids coupled with driver training and education is expected to minimize exit-related injuries.