Limitations in the field of vision of young operators of utility all-terrain vehicles

PROBLEM

All-Terrain Vehicles (ATVs) cause a distressing number of fatalities and injuries among farm youth in the United States. The number of severe injuries caused by ATV crashes on farms, which stood at 25 children in 2019, is expected to rise due to increased ATV sales during the COVID-19 pandemic. Existing research into children's injuries has explored physical capabilities like anthropometry, strength, and visual acuity. Yet, studies assessing youths' physical ability to operate ATVs remain limited. This study tests the hypothesis that diminished vision field in young ATV operators raises crash risks.

METHODS

This study used SAMMIECAD digital human modeling system to simulate and compare the field of vision of youth and adult ATV operators. The simulations incorporated 3-D mockups of ATVs, humans, sprayer tanks, windshields, and obstacles. Ten utility ATVs and children of both genders across nine ages (8-16) and three height percentiles (5th, 50th, 95th) were evaluated.

RESULTS

Simulations showed that young ATV operators generally have a more restricted field of vision than adults, particularly those aged 6-11 years.

DISCUSSION

Visual limitations hinder riders' ability to see ATV controls, potentially leading to vehicle control loss. Moreover, they impair environmental perception during riding, compromising youths' ATV operation abilities and increasing crash risks.

PRACTICAL APPLICATIONS

These findings offer crucial data in support of modifying ATV safety guidelines. Additionally, they can guide youth occupational health professionals in preventing ATV-related incidents in agricultural settings.

Ability of youth operators to reach agricultural all-terrain vehicles controls

PROBLEM

Utility All-Terrain Vehicles (ATVs) are one major cause of youth injuries and fatalities on farms. Utility ATVs have heavy weights and fast speeds that require complex maneuvering. Youth's physical capabilities may not be sufficient to perform those complex maneuvers correctly. Therefore, it is hypothesized that most youth engage in ATV-related incidents because they ride vehicles unfit for them. There is a need to assess ATV-youth fit based on youth anthropometry.

METHOD

This study focused on evaluating potential inconsistencies between the operational requirements of utility ATVs and the anthropometric measures of youth through virtual simulations. Virtual simulations were performed to assess 11 youth-ATV fit guidelines proposed by several ATV safety advocacy organizations (National 4-H council, CPSC, IPCH, and FReSH). In total, 17 utility ATVs along with male-and-female-youth of nine ages (8 to 16 years old) and three height percentiles (5th, 50th, and 95th) were evaluated.

RESULTS

The results demonstrated a physical mismatch between ATVs' operational requirements and youth's anthropometry. For example, male-youth aged 16 of the 95th height percentile failed to pass at least 1 out of the 11 fit guidelines for 35 % of all vehicles evaluated. The results were even more concerning for females. Female youth 10 years old and younger (from all height percentiles) failed to pass at least one fit guideline for all ATVs evaluated.

DISCUSSION

Youth are not recommended to ride utility ATVs.

PRACTICAL APPLICATIONS

This study provides quantitative and systematic evidence to modify current ATV safety guidelines. Furthermore, youth occupational health professionals could use the present findings to prevent ATV-related incidents in agricultural settings.

Ergonomic Evaluation of Manual Weeding Practice and Development of an Ergonomic Solution

Agricultural workers performing manual weeding are exposed to high risks of musculoskeletal disorders to the lower back. Hand weeding exposes workers to sustained static loading to spinal soft tissues, which can lead to the initiation of a cycle of inflammatory response. Assessment of injury risks and investigation of current and new methods of manual weeding are the focus of this study. Nine subjects (7 males and 2 females) participated in this study. Trunk kinematics were monitored while workers performed four weeding tasks using different methods; long- and short-handled weeding (hoe and weed Puller), hand weeding, and a newly developed “Eater”. The Eater consists of two conveyor belts working simultaneously in an intermesh design to simulate the pulling and grabbing action of the hands. Hoe weeding is considered a less hazardous alternative to hand weeding with regards to back injuries but, our results showed otherwise. The worker's sagittal position with the hoe weeding was not significantly different from the short-handled tool. Also, workers weeding with the hoe displayed the highest trunk velocities. On the other hand, the Eater showed promising results by significantly reducing biomechanical risk factors. However, productivity results are not as promising.

The Effects of a Stooped Work Task on the Muscle Activity and Kinematics of the Lower Back

Working in a stooped posture is an important risk factor for low back disorders (LBDs) that requires special focus. Spinal flexion increases the loading on the passive tissues of the lumbar spine compared to neutral postures, yet sustained or repeated flexion reduces the load bearing capability of these tissues. The objective of this study is to assess the effect of performing a stooped work task on the passive tissues of the low back. Passive tissue response is assessed by measuring trunk sagittal range of motion and the occurrence of the flexion-relaxation (F-R) phenomenon at specific times during the work period. Fourteen subjects (10 female and 4 male) were instrumented with a portable data collection system while performing the stooped work task of fresh-market tomato harvest for one hour in the morning and one hour in the afternoon. Results indicate significant changes in the trunk and lumbar sagittal range of motion and F-R after only 11 minutes of stooped work, with few changes for durations up to 55 minutes of work. The potential benefits of short, frequent rest breaks on recovery of passive tissue response are also demonstrated. The data collection device developed for this study allows for further investigation of the effects of stooped work on the lower back, which could lead to improved interventions to reduce LBD risk.

Body-fixed Orientation Sensors for Trunk Motion Sensing

Awkward trunk postures and dynamic trunk movements are associated with increased risk of low back disorders (LBDs). Recent advancements in computing and micro-electromechanical systems (MEMS) technology have resulted in high precision, compact, and relatively inexpensive commercial orientation sensors that address the workplace usage limitations of the most common kinematics measurement methods (video analysis, magnetic field sensors, and electrogoniometers). The purpose of this study is to review the available body-fixed orientation sensing technology for its use in ergonomics research and practice. A laboratory study of a custom MEMS accelerometer-based inclinometer highlights issues of axial orientation, vibration, and non-gravitational acceleration that affect orientation results from basic inclinometers. Techniques are presented for correcting for such issues in advanced sensors using computational methods and combinations of MEMS accelerometers, gyroscopes, and/or magnetometers. Body-fixed orientation sensors provide enhanced opportunities to identify and reduce harmful work postures that may reduce the prevalence and severity of work-related musculoskeletal disorders (WMSDs).

Coactivity Effects upon Carpal Tunnel Contact Forces

Contact force on the carpal tunnel structures due to flexor tendon forces have been identified as an important contributor to the compression of the median nerve. Therefore, a pilot study was conducted to assess the increase in carpal contact force due to the antagonistic coactivity of the finger extensor muscles. Surface EMG activities of the superficial finger flexor and extensor muscles of four subjects were measured during several isometric power grip exertions at seven different wrist angles. The results showed that a linear relation between EMG and muscle force holds under the prescribed isometric conditions. An EMG-assisted model was developed to predict tensile forces in an equivalent flexor tendon. For a given angle, the model predicts increased tensile force in the flexor tendon with increased extensor (antagonist) coactivity in response to isometric grip exertions. It was found that if one accounts for muscle coactivity, predicted force in the flexor tendons would be as much as 33% greater than force predicted by models which neglect coactivity. This increase would also be observed in carpal contact force since this force is linearly related to the flexor tendon force. Models that neglect coactivity severely underestimate flexor tendon forces and consequently contact forces in the carpal tunnel.

Development and Evaluation of Ergonomic Interventions for Bucket Handling on Farms

OBJECTIVE

The aim of this study was to introduce and evaluate two interventions, Ergo Bucket Carrier (EBC) and Easy Lift (EL), for youths (and adults) to handle water/feed buckets on farms.

BACKGROUND

The physical activities of both adult and youth farm workers contribute to the development of low-back disorders (LBDs). Many of the activities youths perform on farms are associated with increased LBD risk, particularly, the handling of water and feed buckets.

METHOD

Seventeen adult and youth participants (10 males and seven females) participated in this study. To assess the risk of LBDs, the participants were instrumented with a three-dimensional spinal electrogonio-meter while lifting, carrying, and dumping water buckets using the traditional method and the two interventions.

RESULTS

For both the adult and youth groups, the results showed that the two interventions significantly decrease the magnitudes of LBD risk in many of the tasks evaluated. Overall, the use of the EBC resulted in a 41% reduction in the level of LBD risk for the carrying task and a reduction of 69% for the dumping task. Using the EL, on the other hand, is especially effective for lifting tasks (55% reduction in LBD risk). Results of the subjective response were consistent with the objective evaluations.

CONCLUSION

This study demonstrated the potential for ergonomic interventions in reducing LBD risk during the common farming task of bucket handling.

APPLICATION

Potential application of this study includes the introduction of the EBC and EL in family farms to reduce the LBD risk among youth and adult farmers.

Migrant women farm workers in the occupational health literature

Little attention has been given to the vulnerable populations of migrant women agricultural workers. A systemic review in PubMed was carried out (1990-2008) using terms related to migrant agricultural workers, with specific focus on women. Case studies from Lebanon and California are presented to highlight key physical, psychosocial, and cultural risk factors among these working populations. The review revealed a host of potential problems that span from pesticide exposure and musculoskeletal disorders to socio-cultural barriers. Comprehensive exposure-outcome and intervention studies focusing specifically on migrant women in agriculture are lacking. In depth studies focusing on the work environment of migrant women workers in the agricultural sector are needed. Personal and environmental factors that influence health should be considered in any effective intervention aiming to influence policy making and have a positive impact on these vulnerable working populations.

Noninvasive high resolution mechanical strain maps of the spine intervertebral disc using nonrigid registration of magnetic resonance images

High resolution strain measurements are of particular interest in load bearing tissues such as the intervertebral disc (IVD), permitting characterization of biomechanical conditions which could lead to injury and degenerative outcomes. Magnetic resonance (MR) imaging produces excellent image contrast in cartilaginous tissues, allowing for image-based strain determination. Nonrigid registration (NRR) of MR images has previously demonstrated sub-voxel registration accuracy although its accuracy and precision in determining strain has not been evaluated. Accuracy and precision of NRR-derived strain measurements were evaluated using computer generated deformations applied to both computer generated images and MR images. Two different measures of registration similarity--the cost function which drives the registration algorithm--were compared: Mutual Information (MI) and Least Squares (LS). Strain error was evaluated with respect to signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and strain heterogeneity. Additionally, the creep strain response from an in vitro loaded porcine IVD is shown and comparisons between similarity measures are presented. MI showed a decrease in strain precision with increasing CNR and decreasing SNR while LS was insensitive to both. Both similarity measures showed a decrease in strain precision with increasing strain heterogeneity. When computer generated heterogeneous strains were applied to MR images of the IVD, LS showed substantially lower strain error in comparison to MI. Results suggest that LS-driven NRR provides a more accurate image-based method for mapping large and heterogeneous strain fields and this method can be applied to studies of the IVD and, potentially, other soft tissues which present sufficient image texture.

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.

Full-time homemakers: workers who cannot "go home and relax"

This paper examined how musculoskeletal disorders (MSDs) of female homemakers were studied in the literature. It also presented preliminary findings from field observations of housework and fulltime homemakers in urban settings. PubMed, Ergonomics Abstracts, Sociofile, and PsycINFO databases were used in the literature search. The review focused on comparing demands of housework and paid work. Also, exposure factors found in studies of various occupations were compared with the results of field observations of housework in 4 homes in Beirut, Lebanon. Few studies systematically examined associations between MSDs and risk factors in housework. Some well-known risk factors for MSDs were identified in the Beirut homes; however, other unique factors were noted. Housework activities expose homemakers to known risk factors for MSDs, which calls for further studies to identify appropriate intervention and prevention strategies.

Limitations in fields of vision for simulated young farm tractor operators

Farm tractors account for the majority of deaths and injuries among youths working on North American farms. A vehicle operator's field of vision is an important operational aspect for safe driving. However, very little is known about visual limitations of young tractor operators compared to adult operators. The main purpose of this study was to quantify limitations in fields of vision of children with different anthropometry. The study was based on assessment of 42 farm tractors in popular use in the USA. The results showed that youth operators typically had diminished fields of vision compared to the average adult operator. The degree of visual limitation is greatest for objects at close distances and when objects are straight in front of the operator/tractor. This has serious implications in terms of risks for runovers, rollovers and collisions. Study findings may help illuminate the development of policies and guidelines in tractor-related jobs for children. STATEMENT OF RELEVANCE: This study provides an ergonomic approach for evaluation of children's visual limitations in tractor operations. This approach could be used in other related cases, where children are allowed to operate vehicles.

Ability of youth operators to reach farm tractor controls

Farm tractor work is commonly assigned to young people on North American farms, where tractors account for the majority of deaths and major portions of non-fatal trauma to working youths. However, little is known about the potential mismatch between the anthropometric and physical characteristics of children and tractor characteristics. The purpose of this study was to evaluate the ability of children of varying ages and percentiles to reach major controls on 45 tractors in common use in the US. The main study finding was that many tractor controls, especially those that are hand-operated, may not be effectively reached by the majority of youth operators aged 12 to 16 years. The study raises further serious questions about the ability of children to safely operate tractors in common use on US farms and calls for reconsideration of age guidelines for the assignment of children to tractor work on farms. This study provides novel ergonomic evidence about the ability of children to reach controls inside agricultural tractor cabins. The approach could be applied in similar situations where youths may operate other vehicles or machines. Study findings support the establishment and refinement of policies and guidelines related to youth tractor operation.

Forces required to operate controls on farm tractors: implications for young operators

Farm tractors account for the majority of fatal injuries to adolescents working in agriculture and therefore remain a leading occupational priority. The question of whether these injuries occur because adolescents are assigned tractor jobs beyond their physical capabilities has not been answered. The purpose of this study was to estimate the activation forces required to operate controls on 40 tractors in common use in the US and compare them with existing estimates of physical strength for children of varying ages and with recommended ergonomic force limits for repeatedly engaging controls. Activation forces for steering, brakes and clutch were measured on each tractor. The main study finding was that the activation forces required to operate tractors typically exceeded the physical abilities of most children aged 13 to 17 years. This raises serious questions about the ability of children to safely operate tractors in common use on US farms. This study provides an ergonomic approach for evaluating the potential mismatch between young people's strength capabilities and forces required in operating farm tractors. This approach could be used in similar situations where adolescents may operate vehicles (e.g. all-terrain vehicles), machinery or other mechanical devices requiring activation of levers and controls. Study findings potentially inform the establishment of occupational policies surrounding tractor operation by young people.

Ergonomic Evaluation of Winegrape Trellis Systems Pruning Operation

The winegrape industry suffers from high incidence rates of work-related musculoskeletal disorders. Pruning of dormant vines is a significant task, requiring long periods of highly repetitive and physically demanding work. The purpose of this study is to quantitatively evaluate five commonly used winegrape trellis systems with regard to the risk of developing musculoskeletal injuries to the wrist and lower back while pruning. Eleven subjects participated in this study. Subjects performed a simulated pruning task as wrist and trunk postures were gathered using electrogoniometers. The results showed significant postural differences among the trellis systems. Compared to the other systems, the VSP was determined to be the optimal system in terms of decreasing relative MSD risk. These results will assist vineyards in the selection process of suitable trellis systems that will include the worker health aspect in conjunction with other trellis-related parameters such as grape quality and productivity.

The effect of feedback training on lumbosacral compression during simulated occupational lifting

This study measured the effect of a feedback training program on lumbar compression during simulated occupational lifting. Two distinct types of feedback were compared: real-time electromyographic feedback, vs. an acceleration index delivered verbally post-lift. Kinematic data were collected from 28 subjects during symmetrical sagittal plane lifts. Following a baseline session, two feedback training sessions were provided, with a 1-week interval between each session. A control group followed the same protocols, but without receiving feedback training. A post-training session, using protocols identical to the baseline session, was used to assess pre-to-post changes in the dependent variable: peak lumbosacral compression computed using a dynamic linked-segment model. All three groups showed reductions in peak compression from pre-to-post: on average the control group improved by 11.2%, the EMG group by 16.7%, and the acceleration group by 25.3%. The results revealed an interaction between the improvement and the group (p=0.023), and a difference between the improvement in the control group and that in the verbal acceleration feedback group (p<0.01). These reductions in lumbosacral compression persisted after a 7-day interval without feedback training, suggesting that this approach could provide sustained risk-reduction during manual materials handling.

In Vitro Measurements of Porcine Anterior Column Units Under Free Swelling

The objectives of this study are to present a 2-D optical method for measuring gross kinematics of porcine anterior column units (ACUs) exposed to swelling with no applied load, provide a detailed error analysis of the 2-D optical measurement technique, and present a 2-D radiographic technique for measuring the distribution of x-ray intensity through an axial slice of the disc. The 2-D optical technique was sufficient for detecting the flexion-extension behavior of the ACUs tested. The error analysis concluded that the use of a second camera to quantify out of plane movement of the specimen would greatly improve the accuracy of the measurement of angle. The 2-D radiographic technique provided limited information on changes in intradiscal material. It was also limited in its accuracy and dependability (i.e., only 5 out of 13 specimens provided radiographs suitable for this analysis). The results of this study indicate that a relationship might exist between the flexion-extension behavior observed from swelling and intradiscal shifts of matter. Further work is needed to confirm this relationship.

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 x 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.

Influence of measurement accuracy on the application of the 1991 NIOSH equation

A relatively neglected topic in manual materials handling (MMH) research is the impact of the accuracy of task parameter measurements on the application of various assessment methods. A laboratory experiment was conducted to investigate the accuracy of NIOSH equation parameter measurements made by eight subjects following a 4-h training session. Five individual tasks were measured; two were single tasks and three were part of a multiple-component simulated palletizing operation. Significant differences between reference parameter measurements and average measurements made by subjects were found. The sensitivity analysis showed that frequency and horizontal location are the most important parameters. These parameters also tended to have the highest measurement errors. Recommendations for increasing the effectiveness of training programs for NIOSH equation users based on the results of the study are presented.

Prospective validation of a low-back disorder risk model and assessment of ergonomic interventions associated with manual materials handling tasks

The evaluation of low-back disorder risk associated with materials handling tasks can be performed using a variety of assessment tools. Most of these tools vary greatly in their underlying logic, yet few have been assessed for their predictive ability. It is important to document how well an assessment tool realistically reflects the job's injury risk, since only valid and accurate tools can reliably determine whether a given ergonomic intervention will result in a future reduction in back injuries. The goal of this study was to evaluate how well a previously reported low-back disorder (LBD) risk assessment model (Marras et al. 1993) could predict changes in LBD injury rates as the physical conditions to which employees are exposed were changed. Thirty-six repetitive materials handling jobs from 16 different companies were included in this prospective cohort study. Of these 36 jobs, 32 underwent an ergonomic intervention during the observation period, and four jobs in which no intervention occurred served as a comparison group. The trunk motions and workplace features of 142 employees performing these jobs were observed both before and after workplace interventions were incorporated. In addition, the jobs' LBD rates were documented for these pre- and post-intervention periods. The results indicated that a statistically significant correlation existed between changes in the jobs' estimated LBD risk values and changes in their actual low-back incidence rates over the observation period. Linear and Poisson regression models also were developed to predict a change in a job's incidence rate and the number of LBD on ajob respectively, as a function of the job's risk change using this assessment model. Finally, this prospective study showed which ergonomic interventions consistently reduced the jobs' mean low-back incidence rates. These results support use of the LBD risk model to assess accurately a job's potential to lead to low-back injuries among its employees.

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 subject's 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.

Regression models for predicting peak and continuous three-dimensional spinal loads during symmetric and asymmetric lifting tasks

Most biomechanical assessments of spinal loading during industrial work have focused on estimating peak spinal compressive forces under static and sagittally symmetric conditions. The main objective of this study was to explore the potential of feasibly predicting three-dimensional (3D) spinal loading in industry from various combinations of trunk kinematics, kinetics, and subject-load characteristics. The study used spinal loading, predicted by a validated electromyography-assisted model, from 11 male participants who performed a series of symmetric and asymmetric lifts. Three classes of models were developed: (a) models using workplace, subject, and trunk motion parameters as independent variables (kinematic models); (b) models using workplace, subject, and measured moments variables (kinetic models); and (c) models incorporating workplace, subject, trunk motion, and measured moments variables (combined models). The results showed that peak 3D spinal loading during symmetric and asymmetric lifting were predicted equally well using all three types of regression models. Continuous 3D loading was predicted best using the combined models. When the use of such models is infeasible, the kinematic models can provide adequate predictions. Finally, lateral shear forces (peak and continuous) were consistently underestimated using all three types of models. The study demonstrated the feasibility of predicting 3D loads on the spine under specific symmetric and asymmetric lifting tasks without the need for collecting EMG information. However, further validation and development of the models should be conducted to assess and extend their applicability to lifting conditions other than those presented in this study. Actual or potential applications of this research include exposure assessment in epidemiological studies, ergonomic intervention, and laboratory task assessment.

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 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.

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 of 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.

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.

A method for measuring external spinal loads during unconstrained free-dynamic lifting

Biomechanical lifting models often require the knowledge of the applied trunk moments and forces for model validation purposes and/or to determine loading levels experienced at various joints of the body. Trunk kinetic data under dynamic exertions are commonly difficult to attain without restrictive anatomic/anthropometric assumptions and cost or constraining body motion. The main objectives of the study were to present a new technique for determining continuous three-dimensional forces and moments about the L5/S1 spinal joint, and to validate the technique and assess its applicability under lifting situations. A combination of a force plate and two electrogoniometers facilitated the determination of trunk kinetics about L5/S1. An apparatus was devised to allow the application of various actual moments that were compared to their corresponding predicted moments. The results showed that, over all the conditions considered, the average percent error in estimating the actual applied moment(s) was about 4% (2.3 S.D.), with a test-retest reliability approaching unity. Given such agreement, along with the relative ease and directness of the method, it is believed that this approach should be applicable under most lifting conditions. The technique offers a fairly accurate measure of trunk moments without the need for constraining the motion of any body joint.

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 worker's capacity to adopt particular techniques. Risk factors are also adjusted in relation to the worker's 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.

Diurnal variation in trunk kinematics during a typical work shift

Diurnal variation in trunk flexibility, defined as changes in range of motion, has been previously observed and quantified. Prior studies have shown that decreased disk height occurs as the day progresses and allows the spinal ligaments to slacken, resulting in an increase in the range of motion (flexibility) and a possible reduction in the risk of injury. This risk may be accentuated under dynamic motions of the spine. This study was conducted to observe the change in dynamic trunk mobility as a function of time of the day. Trunk motions of 21 men were observed at three specific times of the day using a triaxial electrogoniometer. No variation in trunk range of motion in any of the cardinal planes was observed. However, velocity and acceleration in the sagittal plane showed significant variations, suggesting the reexamination of the "slack ligaments" hypothesis. This study asserts that identifying flexibility by only its static component, range of motion, gives only partial information about the diurnal variation experienced by the spine. Industrial injuries occurring in the early morning hours may be a result of insufficient trunk mobility. This study indicates that risk associated with diurnal variation is far more complex than originally thought.

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.

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.