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The effects of operator position, pallet orientation, and palletizing condition on low back loads in manual bag palletizing operations
... The study of [49] analyzed the design of operator workstations and their effect on reducing the worker injury risk. Its results clearly demonstrated "that positioning the pallet at the end of a conveyor belt, results in a significant reduction in loading on the lumbar spine compared to positioning the pallet on the side of the conveyor, most likely due to the ability of using the momentum of the bag as it comes off of the conveyor as opposed to having to forcefully redirect the bag from its course along the conveyor when the pallet is located on the side" [49]. ...
... The study of [49] analyzed the design of operator workstations and their effect on reducing the worker injury risk. Its results clearly demonstrated "that positioning the pallet at the end of a conveyor belt, results in a significant reduction in loading on the lumbar spine compared to positioning the pallet on the side of the conveyor, most likely due to the ability of using the momentum of the bag as it comes off of the conveyor as opposed to having to forcefully redirect the bag from its course along the conveyor when the pallet is located on the side" [49]. Additionally, the study showed that controlled lower-level loading has a higher impact on the pressure exerted on the spine. ...
... The way to reduce this loading was either by raising the pallet level, or by loading the pallet with the help of uncontrolled drop stacking. It was posited that lumbar compression for the drop technique was approximately 600-800 N lower than those for controlled placement at the lower levels [49]. ...
Technology has disrupted each current industry, and supply chain is not going to be an exception. Businesses are already starting to establish interconnected global networks of Cyber-Physical Systems with the help of the Internet of Things and Cloud Computing. In this context, the chapter will debate aspects related to the new challenges of reducing ergonomics risks in manufacturing warehouse logistics by valorizing emerging technologies to create workplace wellbeing. After an extended literature review regarding the relevant ergonomics approaches in warehouse logistics, there will be presented some warehouse ergonomics solutions to be considered for the next generation of logistics system. The solutions described will refer to the monitoring and improvement of the ergonomic reality. Finally, conclusions and future trends will end the chapter.
... In this regard, the study of Mir Mohammadi et al. among food industry's workers attributed to the amount of compressive force on the waist to the weight of the load, unfavorable posture, and anthropometric dimensions of individuals [17]. A study by Gallagher et al. (2015) showed that lifting 11.3 kg load packages increased the compressive force on the waist to above 3400 N, which is more dangerous if the load is increased to 23-45 kg [26]. In this study, which carried blocks of 12-15 kg, about 45% of people felt a compressive force higher than 3400 N. In some cases, block-making workers had to lift two blocks at the same time, which could increase the compressive force. ...
... In this regard, the study of Mir Mohammadi et al. among food industry's workers attributed to the amount of compressive force on the waist to the weight of the load, unfavorable posture, and anthropometric dimensions of individuals [17]. A study by Gallagher et al. (2015) showed that lifting 11.3 kg load packages increased the compressive force on the waist to above 3400 N, which is more dangerous if the load is increased to 23-45 kg [26]. In this study, which carried blocks of 12-15 kg, about 45% of people felt a compressive force higher than 3400 N. In some cases, block-making workers had to lift two blocks at the same time, which could increase the compressive force. ...
... Furthermore, it was found that the compressive and shear force was related to the BMI of individuals [28]. In a study by Gallagher et al., whenever pallet was next to the conveyor the shear force on the lower levels of the pallet was 800 N, which causes the forward bend to the peak [26]. In this study, about 12 people felt a shear force higher than 500 N. ...
Due to the negative influence of manual load handling on the lower back, it leads to low back disorders and high mechanical loads. The present study was aimed to investigate forces exerted on the lower back during manual handling in young workers in selected block-making workshops. This descriptive, cross-sectional study was carried out on 40 young workers with an average age of 31 years old in several block-making industries in 2020. 3DSSPP Software was used for biomechanical analysis of the forces exerted on the lower back. The prevalence of musculoskeletal disorders was assessed using the Standard Cornell Questionnaires. Spearman, Friedman, and ANOVA correlation tests via SPSS software version19 were used to determine the relationship between demographic variables, the prevalence of musculoskeletal disorders, the relationship between the prevalence of musculoskeletal disorders, the amount of compressive, and shear forces on workers' backs. The results showed that the mean compressive and shear forces exerted to the lumbosacral joint (L5/S1) were 3194.85 ± 1064.326 and 473.17 ± 89.451 N, the intervertebral disc (L4/L5) were 3924.78 ± 4344.87 and 383.18 ± 154.554. The findings also indicated that the highest prevalence of pain was related to the lower back 45% and right knee 30%. There was a significant relationship between the mean score of musculoskeletal disorders obtained from the Cornell questionnaire with age, work experience, and weight and body mass (0.001> P). The shear forces exerted to the lower back were higher than the permissible levels by 30% to 37% of respondents, and on average 42.5% of them experienced compressive forces. Thus, it can cause a lot of injuries to the back if lasts for a long time. The results showed that manual load handling was dangerous for this group's ages. Consequently, people may suffer serious injuries and disorders particularly lower back disorders.
... This criterion was first proposed in the 1981 original NLE and was maintained in the RNLE [5,6]. Until now, it is widely used as a major criterion for the assessment of manual lifting tasks [8][9][10][11][12][13][14][15]. ...
... The evaluation of manual work based on lumbar compressive forces can be seen in the works of Merryweather et al. [34], Arjmand et al. [12,35], Gallagher and Heberger [14], and Ray et al. [13]. Most of these works refer to NIOSH lumbar compressive force of 3.4 kN as a criterion; however, our injury risk curves demonstrated a higher risk for this value for individuals with higher ages. ...
... Resultant coefficients of the risk curve for specific ages, fitted to Eq.14 ...
Abstract This study introduces injury risk curves for the lumbar spine for use in the risk assessment of low back pain (LBP) caused by manual lifting of heavy loads. LBP has been a longstanding problem among industrial workers, giving rise to the development of assistive devices. However, quantitative evaluation methods to verify the safety of such devices have not yet been established. The notable biomechanical criterion of 3.4 kN of lumbar compressive force, defined by the National Institute for Occupational Safety and Health, applies only to young, healthy workers with a fixed risk level. This study on injury risk curves clarified the risk level of injury to the lumbar spine due to lumbar compressive force for individuals within a wide age range. The findings can be applied for the design and evaluation of assistive devices as well as the design of ergonomic guidelines for manual work.
... Individually wrapped or packaged foods must be loaded onto pallets or other tertiary packaging to facilitate shipping. Doing this manually can lead to strain and potential injuries (Gallagher & Heberger, 2015), so automated palletizers were developed to reduce ergonomic strain. Many of the automated systems depend on robotics to increase efficiency and ergonomics (Wilson, 2010), but automated and robotic palletizers present their own hazards to workers (OSHA, 2009). ...
... Past research has suggested that management may not willingly invest in safety and health systems within their supply chain (Walters & James, 2011); it could be the case that customer-facing supply chain partners or policymakers will have to take a larger role as part of their ESG (environment, social, governance) initiatives. Research in other industries has shown that ergonomic-focused solutions can reduce operator stress and strain (Gallagher & Heberger, 2015), but it is unknown whether those changes would impact severe injury rates. The food supply chain might, with its reliance on a combination of manual labor and machinery to move product, be an ideal case study to investigate how better ergonomics impacts injury rates. ...
Introduction:
The modern food supply chain presents unique hazards to employees that result in higher morbidity and mortality rates versus other industries. Employees in food manufacturing, wholesaling, and even retailing experience relatively high numbers of occupational injuries and fatalities. One reason for the high hazard rates may be the reliance on a synergistic packaging system designed to load and transport food products within and between manufacturers, wholesalers, and retailers. Packaged food products are often aggregated using palletizers before they can be transported by forklifts and pallet jacks. Materials handling within facilities is critical to the efficient functioning of all members of the food-related supply chain, but product movement can be a source of occupational injuries. No previous research has examined the cause and result of such hazards.
Method:
This paper aims to examine severe injuries related to the packaging and movement of food products in segments of the food and beverage supply chain from manufacturing to retailing. An OSHA database was used to investigate all severe injuries in the six years from 2015 to 2020. The focus was on the food supply chain for the period since OSHA began mandating new reporting procedures for severe injuries.
Results:
Results show there were 1,084 severe injuries and 47 fatalities during the six-year period. Fractures of the lower extremities were most prevalent, with the most frequent event type being transportation-related such as pedestrian-vehicle incidents. Significant differences were seen in the three parts of the food supply chain.
Practical applications:
Implications are drawn for key sectors of the food-related supply chain to reduce packaging- and product movement-related hazards.
... Occupational-related physical activity involves repeated or sustained exertions of the body while often in biomechanically awkward postures. They include occupational computer work, hand tool use, and intense practice and playing of muscle instruments, in which there is prolonged positioning of the neck and shoulders in one position (20)(21)(22)(23) or prolonged and sustained gripping and redundant movement of the thumb and digits (21,(23)(24)(25)(26). Occupational-related physical activity also includes manual material handling tasks that require lifting/lowering, pushing/pulling, and holding/carrying loads (27,28). Work-related musculoskeletal disorders (MSDs) encompass rotator cuff tears, tendinitis, arthritis, carpal tunnel syndrome, and more (25,(29)(30)(31). ...
... The degenerative changes are thought to be due to enhanced mechanical overloading and shocks to the spinal column that increase internal lumbar vertebral load (compressive and shear peak forces) (59). Individual differences likely also alter ultimate stress values to the same load before rapid damage accumulation occurs in involved tissues, for example, differences in muscle mass, strength, kinematic strategies, and experience-driven differences in muscle recruitment patterns (27,65). ...
It is commonly assumed that beneficial adaptations in bone occur with vigorous exercise, yet any adaptive re/modeling in bone undergoing persistent overloading can be counteracted by superimposed inflammatory, compressive and tensile-loading induced damage responses above thresholds of tissue fatigue failure and repair. This leads to a tenuous balance between achieving bone accrual versus loss.
... In this task, the frequency of each posture assumed to fill a bag is higher with a shorter duration for each posture. Further, manual bagging task is carried out in several other industries such as rice milling, animal feed milling etc., mainly in developing countries (Gallagher & Heberger, 2015). Previous studies found that lower back MSDs or ergonomic hazards are associated with bending the trunk frequently, heavy or awkward lifting, bending or twisting the neck (Dong et al., 2019;Shockey et al., 2018) and frequent lifting, pushing, and pulling (Shockey et al., 2018) for different jobs. ...
Filling paddy bags by hand is a common task during harvesting, but it can cause musculoskeletal disorders (MSDs) in various body regions. The current study aims to evaluate posture and find an association between MSDs and body posture scores. The Nordic questionnaire and rapid entire body assessment (REBA) were used to collect MSDs and postures from farmers. The MSD in various body regions (neck, elbows, hands, upper back, knees, ankles, lower back, hips, thighs, and buttocks) was found to be 6.7%, 10%, 3.3%, 6.7%, 16.7%, 20%, and 10%, respectively, during the last 12-month period. In REBA score findings, holding bags, filling the bucket, and the bag were found to have a very high risk of causing MSDs. Despite the fact that MSDs are not very common among farmers who engage in paddy bagging tasks, posture analysis reveals what causes MSDs. Further investigation is needed to improve and reduce MSDs.
... The relationship between awkward posture (e.g., twisting) and the risk of work-related musculoskeletal disorders (WMSDs) was previously evidenced [5]. Most research has focused on the effects of the twisting movement on lumbar moments [6] or ergonomic assessment scores [4]. Upper-limb injuries are a major complaint in the workplace among janitorial workers [7], physical therapists [8], etc. ...
A trunk-twisting posture is strongly associated with physical discomfort. Measurement of joint kinematics to assess physical exposure to injuries is important. However, using a single Kinect sensor to track the upper-limb joint angle trajectories during twisting tasks in the workplace is challenging due to sensor view occlusions. This study provides and validates a simple method to optimally select the upper-limb joint angle data from two Kinect sensors at different viewing angles during the twisting task, so the errors of trajectory estimation can be improved. Twelve healthy participants performed a rightward twisting task. The tracking errors of the upper-limb joint angle trajectories of two Kinect sensors during the twisting task were estimated based on concurrent data collected using a conventional motion tracking system. The error values were applied to generate the error trendlines of two Kinect sensors using third-order polynomial regressions. The intersections between two error trendlines were used to define the optimal data selection points for data integration. The finding indicates that integrating the outputs from two Kinect sensor datasets using the proposed method can be more robust than using a single sensor for upper-limb joint angle trajectory estimations during the twisting task.
... Barim, Lu showed that IMU sensors provide inaccurate information about hand location with respect to the body during lifting [53]. Such information represents a critical limitation for using an IMU system to assess MMH activities, as the horizontal distance between the load being lifted and the body has been shown as a major workplace risk factor [13,65,66]. Also, another critical factor in the MMH activities risk assessment is the spinal loadings. ...
Quantifying the workplace risk factors such as body inclination angles, load weights, and vertical and horizontal reaching distances is essential to prevent work-related musculoskeletal disorders. Most of these factors need to be measured during the task. Assessing the work performed using a direct observation approach is time consuming and the study can encounter observational errors as well as disturb the workers. Wearable sensing technologies could replace the use of optical motion capturing systems. No review study was conducted to discuss the use of wearable technology as a means for providing input variables for various manual material handling job assessment methods. The current study provides a review about wearable technologies that can be used to provide input variables for different ergonomic assessment methods. The validity of diverse wearable sensors in quantifying different biomechanical measures is included. Also, the synchronization of those measures with various ergonomic assessment methods is discussed.
... To that end, the effect of material handling in distribution centers and warehouses has been investigated in terms of back and shoulder biomechanics [23][24][25][26][27][28]. Gallagher and Heberger [29] have investigated the biomechanical demands on the lower back during the lifting and lowering of bags in mining commodity warehouses for different pallet layouts. Moreover, Jorgensen et al. [30] explored the effect of pallet distance from the storage site on worker biomechanics to evaluate the risk of development of lower back disorders. ...
Repetitive task performance is a leading cause of musculoskeletal injuries among order-picking workers in warehouses. The repetition of lifting tasks increases the risk of back and shoulder injuries among these workers. While lifting in this industry is composed of loaded and unloaded picking and placing, the existing literature does not address the separate analysis of the biomechanics of the back and shoulder for these events. To that end, we investigated the kinematics of the back and shoulder movements of nine healthy male participants who performed three sessions of a simulated de/palletization task. Their back and shoulder kinematics were sensed using an optical motion capture system to determine the back inclination and shoulder flexion. Comparison of the kinematics between the first and last sessions indicated statistically significant changes in the timings, angles, coordination between the back and shoulder, and moments around the shoulder (p<0.05). The majority of the significant changes were observed during the loaded events, which confirms the importance of the separation of these events for biomechanical analysis. This finding suggests that focusing worker evaluation on the loaded periods can provide important information to detect kinematic changes that may affect musculoskeletal injury risk.
... Corrugated boxes manufacturer uses automation for their production processes except the palletizing task [2]. Palletizing is done by at least two workers whose task is to stack the boxes on the pallet to prepare the products for delivery. ...
... In addition, the need for a human operator to take over should be considered, especially as skill loss could occur over a prolonged period. The skill loss is not only attributed to knowledge of the task, but learned efficiencies in performing physically demanding jobs, such as that seen in palletizing operations where the momentum of the conveyer is used to assist loading pallets at bagging operations [64]. Hence, adopting a macroergonomic or sociotechnical perspective of automated systems design and function allocation would not only improve the overall efficiency of the system, but improve the mine worker's overall quality of life [65]. ...
Ergonomics is the scientific discipline that investigates the interactions between humans and systems to optimize both human and system performance for worker safety, health, and productivity. Ergonomics is frequently involved either in the design of emerging technologies or in strategies to alleviate unanticipated human performance problems with emerging technologies. This manuscript explores several such emerging issues and opportunities in the context of the mining sector. In mining, the equipment, tools, and procedures have changed considerably and continue to change. Body-worn technology provides a number of opportunities to advance the safety and health of miners, while teleoperation and autonomous mining equipment stand to benefit significantly from ergonomics applications in other sectors. This manuscript focuses on those issues and opportunities that can impact the safety and health of miners in the near term.
... The MMH can cause mental and physical illness in human workers, decreasing material handling efficiency. Hence the prime objective of the dissertation work is to implement an alternative solution to palletizing which is economic, efficient, involving minimum repair & maintenance and flexible in operations so as to increase the productivity in automation [1]. ...
... Typical plastic shopping bags leave marks on the hands and cause discomfort if they are loaded and held for a period because of the large amounts of stress that are concentrated in their relatively thin handles [16,17]. By using shopping bag handle, shoppers can easily transport filled plastic grocery bags without enduring pain associated with grasping the handles of the bags with their fingers [18,19]. ...
Background:
Plastic shopping bags are used world over. However, users may suffer pain in or injury to their fingers because of the relatively thin plastic handles of those bags. Due to such drawbacks of the available bag handles, new designs are needed.
Objective:
The purpose of this study was to develop a handle that can be used to carry many bags simultaneously. This handle was ergonomically designed and manufactured with soft grip. Then, an experiment was performed to test the usefulness of the developed handle.
Methods:
The cardiac cost, discomfort ratings, activity levels of eight muscles, and peak plantar pressure (PPP) were the response variables in the experiment. The carrying style (with or without the handle), carrying method (dominant hand or both hands), and weight carried (5%, 10%, or 15% of the subject's body weight) were the independent variables in the experiment. Twenty-six healthy, young volunteers participated in the experiment.
Results:
It was found that carrying grocery bags in both hands using the bag handle was preferable to the other carrying methods because it reduced the cardiac cost, muscular stress, PPP, and average discomfort ratings.
Conclusion:
The results of this study demonstrated that the developed shopping bag handle provides an ergonomic solution for carrying multiple heavy plastic bags.
... While automation is the ideal solution for manual palletising stations and mechanical aids such as vacuum lifts are secondary, the authors wanted to provide recommendations for palletising stations layouts to minimise biomechanical loading when palletising could not be automated or mechanised. To this end, a laboratory study was carried out to investigate the effects of operator and pallet positions relative to the conveyor belt on biomechanical loading of the low-back (Gallagher and Heberger 2015). Positioning the pallet at the end of the conveyor resulted in significantly lower forward bending moments as compared to pallets placed at the side of the conveyor. ...
The development and testing of ergonomics and safety audits for small and bulk bag filling, haul truck, and maintenance and repair operations in coal preparation and mineral processing plants found at surface mine sites is described. The content for the audits was derived from diverse sources of information on ergonomics and safety deficiencies including: analysis of injury, illness, and fatality data and reports; task analysis; empirical laboratory studies of particular tasks; field studies and observations at mine sites; and maintenance records. These diverse sources of information were utilized to establish construct validity of the modular audits that were developed for use by mine safety personnel. User and inter-rater reliability testing was carried out prior to finalizing the audits. The audits can be implemented using downloadable paper versions or with a free mobile NIOSH-developed Android application called ErgoMine.
Practitioner Summary
The methodology used to develop ergonomics audits for three types of mining operations is described. Various sources of audit content are compared and contrasted to serve as a guide for developing ergonomics audits for other occupational contexts.
Musculoskeletal disorders (MSDs) account for a large societal and economic burden throughout the world. In this chapter, the authors begin by providing a brief review of some of the more common MSDs, providing descriptions and characteristic features of the disorders, prevalence and incidence data, relevant anatomy and pathology, and the risk factors or activities associated with the development of the disorders. The common MSDs include low back pain, hand & wrist tendinopathy, lateral tendinopathy of the elbow, medial tendinopathy of the elbow, shoulder tendons, muscle fatigue, myalgia, muscle fibrosis, carpal tunnel syndrome, ulnar tunnel syndrome, and hand‐arm vibration syndrome. The authors also discuss some of the more common upper extremity disorders, their characteristics, prevalence and incidence, anatomy and pathology, and risk factors.
Material handling injuries reported to the U.S. Mine Safety and Health Administration (MSHA) result in nearly 70,000 days of work lost each year. Several mitigation efforts for these injuries focus on the back, but shoulder injuries account for four times the days lost. Nonfatal incidents reported to MSHA from 2013 through 2017 were limited to shoulder sprains and strains and were analyzed to determine what contributed the most to these injuries. Injuries were coded based on the task performed, motions involved, and the tools used. The analysis indicated that auto maintenance and tasks involving loading/unloading supplies led to the highest number of injuries. Many of these injuries were related to operating equipment or the use of specific tools. The injuries often involved lifting/lowering or pulling/pushing movements. These findings suggest future mitigation strategies for the risk of shoulder sprains and strains should focus on auto maintenance and tasks involving loading/unloading supplies.
Occupational Applications
There is an increased risk of developing low back pain when lifting objects closer to the floor when compared to lifting at waist height. These results support the key message of “Store-it-off- the-floor”, which small businesses can easily implement to identify and control lifting hazards in their workplaces. Since the majority of the workforce is comprised of small businesses, ergonomic solutions (e.g., Store-it-off-the-floor) should be designed to take into account the special challenges small businesses often face when trying to implement musculoskeletal disorder prevention activities, such as limits on time, knowledge, and budget.
Technical Abstract
Background: Manual materials handling (MMH) is a common hazard for workplace injuries such as low back pain. Although the risk factor of lifting height has been shown in the literature to be a large contributor to low back injury incidence, currently there have been no attempts to consolidate this information into a form suitable for knowledge dissemination.
Purpose: The purpose of this study was to summarize the effects of lifting height on low back loading and the risk of developing low back pain.
Methods: Three electronic databases (PubMed, Scopus, and Ergonomic Abstracts) were searched to find studies that could document the effect of lifting at various heights on low back loading.
Results: In total, 35 studies had outcome measures that were included in the analysis and interpretation for this paper. Lifting from the floor was reported to produce up to twice the amount of spinal loading as lifting from a more desirable location, such as elbow height. This evidence supports a focus on avoiding lifting from low heights: below the knee and especially from the floor. Lifting from the floor also magnified the deleterious effects of MMH on workers with low back pain symptoms, older workers, workers with knee osteoarthritis, and workers with high Body Mass Index.
Conclusions: The results of this review support a knowledge dissemination campaign targeting lifting from the floor as both a method for hazard identification and as the basis of controls in workplaces with little ergonomics knowledge, or in small business.
Bagging operations are common in the mining industry and are associated with numerous musculoskeletal injuries. To better understand the physical demands of bagging operations, field evaluations quantifying low back loading and physiological costs of bagging tasks were performed at two bagging operations. A biomechanical model employing electromyography (EMG) and goniometry was used to estimate lumbar compression and a portable metabolic system used to assess heart rate and oxygen consumption. Manual palletizing of bags was found to generate a load of approximately 1,500 Newtons on the spine, with a few larger loads of 2,000-3,000 Newtons. The average oxygen cost for stacking was 5.3 METS, indicating moderately intense physical activity. Bag filling resulted in lower lumbar loads and a reduced physiological cost (3.2 METS), or a moderate level of energy expenditure. Use of a vacuum hoist resulted in a 39% reduction in the peak compressive load on the worker’s spine compared to manual lifting when palletizing 75-lb bags.
Although ergonomics audits are commonly used by consultants, the scientific literature on reliable and valid audits is sparse. This paper describes a multi-faceted methodological approach to developing ergonomics audits for three types of mining operations. The approach was derived from a validated audit (Ergonomics Assessment Program (ERNAP)) for aircraft maintenance operations. While there were contextual, regulatory, and intended end user differences, the general approach to establishing content validity through task analysis and workplace observations, surveillance data, and accepted practices and regulations proved to be effective, albeit with modifications. Analysis of fatality reports and desire for integration with existing mining safety approaches were two areas where the current approach differed from ERNAP.
We examined the relationship of musculoskeletal risk factors underlying force and repetition on tissue responses in an operant rat model of repetitive reaching and pulling, and if force x repetition interactions were present, indicative of a fatigue failure process. We examined exposure-dependent changes in biochemical, morphological and sensorimotor responses occurring with repeated performance of a handle-pulling task for 12 weeks at one of four repetition and force levels: 1) low repetition with low force, 2) high repetition with low force, 3) low repetition with high force, and 4) high repetition with high force (HRHF).
Rats underwent initial training for 4--6 weeks, and then performed one of the tasks for 12 weeks, 2 hours/day, 3 days/week. Reflexive grip strength and sensitivity to touch were assayed as functional outcomes. Flexor digitorum muscles and tendons, forelimb bones, and serum were assayed using ELISA for indicators of inflammation, tissue stress and repair, and bone turnover. Histomorphometry was used to assay macrophage infiltration of tissues, spinal cord substance P changes, and tissue adaptative or degradative changes. MicroCT was used to assay bones for changes in bone quality.
Several force x repetition interactions were observed for: muscle IL-1alpha and bone IL-1beta; serum TNFalpha, IL-1alpha, and IL-1beta; muscle HSP72, a tissue stress and repair protein; histomorphological evidence of tendon and cartilage degradation; serum biomarkers of bone degradation (CTXI) and bone formation (osteocalcin); and morphological evidence of bone adaptation versus resorption. In most cases, performance of the HRHF task induced the greatest tissue degenerative changes, while performance of moderate level tasks induced bone adaptation and a suggestion of muscle adaptation. Both high force tasks induced median nerve macrophage infiltration, spinal cord sensitization (increased substance P), grip strength declines and forepaw mechanical allodynia by task week 12.
Although not consistent in all tissues, we found several significant interactions between the critical musculoskeletal risk factors of force and repetition, consistent with a fatigue failure process in musculoskeletal tissues. Prolonged performance of HRHF tasks exhibited significantly increased risk for musculoskeletal disorders, while performance of moderate level tasks exhibited adaptation to task demands.
Our aims were (a) to perform a systematic literature review of epidemiological studies that examined the interaction of force and repetition with respect to musculoskeletal disorder (MSD) risk, (b) to assess the relationship of force and repetition in fatigue failure studies of musculoskeletal tissues, and (c) to synthesize these findings.
Many epidemiological studies have examined the effects of force and repetition on MSD risk; however, relatively few have examined the interaction between these risk factors.
In a literature search, we identified 12 studies that allowed evaluation of a force-repetition interaction with respect to MSD risk. Identified studies were subjected to a methodological quality assessment and critical review. We evaluated laboratory studies of fatigue failure to examine tissue failure responses to force and repetition.
Of the 12 epidemiological studies that tested a Force x Repetition interaction, 10 reported evidence of interaction. Based on these results, the suggestion is made that force and repetition may be interdependent in terms of their influence on MSD risk. Fatigue failure studies of musculoskeletal tissues show a pattern of failure that mirrors the MSD risk observed in epidemiological studies.
Evidence suggests that there may be interdependence between force and repetition with respect to MSD risk. Repetition seems to result in modest increases in risk for low-force tasks but rapid increases in risk for high-force tasks. This interaction may be representative of a fatigue failure process in affected tissues.
Awkward trunk posture during work can be caused by a number of controllable factors, including poor work station layout, inappropriate design of tools and equipment, and/or incorrect work methods. If not eliminated, these postures can cause fatigue and contribute to the development of pain and disorders in the lower back.A computer-aided system was developed to evaluate trunk posture during work by measuring the time spent in neutral and non-neutral postures. This system was used to assess postural risk factors in a case-referent study of back disorders in an automobile assembly plant. The use of non-neutral trunk postures, such as forward flexion, lateral bending, and axial twisting, was associated with reports of back pain.The results of this study suggest that job redesign and/or other methods for controlling non-neutral posture be implemented to reduce the risk of back pain on industrial jobs. A general approach to work station design, based on a mechanical model of the human skeletal system, is described. This model is used to develop specific job-design guidelines to prevent awkward trunk posture.
Study Design. A 3-year prospective cohort study among workers of 34 companies in the Netherlands.
Objectives. To investigate the relation between flexion and rotation of the trunk and lifting at work and the occurrence of low back pain.
Summary of Background Data. Previous studies on work-related physical risk factors for low back pain either lacked quantification of the physical load or did not take confounding by individual and psychosocial factors into account.
Methods. The study population consisted of 861 workers with no low back pain at baseline and complete data on the occurrence of low back pain during the 3-year follow-up period. Physical load at work was assessed by means of analyses of video-recordings. Information on other risk factors and the occurrence of low back pain was obtained by means of self-administered questionnaires.
Results. An increased risk of low back pain was observed for workers who worked with the trunk in a minimum of 60° of flexion for more than 5% of the working time (RR 1.5, 95% CI 1.0–2.1), for workers who worked with the trunk in a minimum of 30° of rotation for more than 10% of the working time (RR 1.3, 95% CI 0.9–1.9), and for workers who lifted a load of at least 25 kg more than 15 times per working day (RR 1.6, 95% CI 1.1–2.3).
Conclusions. Flexion and rotation of the trunk and lifting at work are moderate risk factors for low back pain, especially at greater levels of exposure.
Bolting large sheets of wire mesh screen (WMS) to the roof of underground mines prevents injuries due to rock falls. However, WMS can be heavy and awkward to lift and transport, and may result in significant spinal loading. Accordingly, six male subjects (mean age = 45.8 years + 7.5 SD) were recruited to lift WMS in a laboratory investigation of the biomechanical demands. Biomechanical modeling was used to estimate external moments about L5–S1 for sixteen lifting tasks, using two sizes of WMS. Full-size WMS involved a two-person lift, while half-size WMS involved a one-person lift. Lifts were performed under 168 cm and 213 cm vertical space. Restriction in vertical space increased the maximum L5–S1 extensor moment from 254 to 274 Nm and right lateral bending moment from 195 to 251 Nm. Lifting full sheets of screen (as opposed to half sheets) resulted in an average 33 Nm increase in L5–S1 extensor moment. The L5–S1 extensor moment was increased by an average of 44 Nm (18%) when lifting screens positioned flat on the floor compared to an upright position.Relevance to industryLarge flexible materials are commonly lifted in industrial work environments, and may involve the efforts of two or more workers. The current study examines the low back loading associated with lifting large flexible screens and presents recommendations to reduce spine loading.
Masonry workers face some of the highest physical demands in the construction industry where large bags of masonry material weighing 42.7 kg are commonly handled by mason tenders who mix the mortar, distribute mortar and bricks/blocks, and erect/dismantle scaffolding throughout the day. The objective of this study was to determine the effectiveness of using half-weight bags (21.4 kg) on reducing the biomechanical loading, physiological response, and perceived exertions. Ten male subjects performed asymmetric lifting tasks simulating unloading bags from a pallet. Muscle activity, trunk kinematics, heart rate, blood pressure and subjective rating data were collected. Spine loads were predicted from a well-validated EMG-assisted model. Bag weight, lift type, bag height at origin, and asymmetry at destination significantly impacted the spine loads. While there was a 50% reduction in bag weight, the peak loads for the half-weight bags were only 25% less than the more available full-weight bags (a reduction of about 320 N of shear and 1000 N of compression). Lifts allowing movement of the feet reduced the loads by about 22% in shear and 27% in compression compared to constrained postures. Interestingly, cumulative spine loads were greater for the lighter bags than the heavy bags ( approximately 40%). The subjective ratings of exertion and risk were significantly lower for the lighter bags. RELEVANCE TO INDUSTRY: The reduction in peak spine loading for the half-weight bags, particularly at the higher heights and when the feet were allowed to move could significantly reduce the injuries of masonry workers. However, there were trade-offs with cumulative loads that may minimize the reduced risk. Overall, given the limited amount of time lifting bags, the reduction of peak loads.
The method of force application and the statistical index used are clearly stated in only about 10% of the literature on human strength. A small working group discussed problems of definition, methodology, etc. and have come to some tentative conclusions which it is felt will aid in the collection of data which will provide reasonably firm bases for decision making. It is concluded that the instructional set exerts an influence on the measure of strength, and that without explicit instructions subjects tend to develop their own strategies reflecting their diverse interpretation of the task. A standard procedure is proposed. The results of their study emphasize the necessity for explicit instructions to subjects in strength assessment studies, and the importance of reporting in detail all factors which influence the generation of force and its application to a transducer. Had an effort been made to define strength, and an agreement been reached about reporting all relevant details of assessment studies in years past, handbooks, texts, etc. would now contain information more directly usable by human factors specialists, plant safety officers, and others.
In 1985, the National Institute for Occupational Safety and Health (NIOSH) convened an ad hoc committee of experts who reviewed the current literature on lifting, recommend criteria for defining lifting capacity, and in 1991 developed a revised lifting equation. Subsequently, NIOSH developed the documentation for the equation and played a prominent role in recommending methods for interpreting the results of the equation. The 1991 equation reflects new findings and provides methods for evaluating asymmetrical lifting tasks, lifts of objects with less than optimal hand-container couplings, and also provides guidelines for a larger range of work durations and lifting frequencies than the 1981 equation. This paper provides the basis for selecting the three criteria (biomechanical, physiological, and psychophysical) that were used to define the 1991 equation, and describes the derivation of the individual components (Putz-Anderson and Waters 1991). The paper also describes the lifting index (LI), an index of relative physical stress, that can be used to identify hazardous lifting tasks. Although the 1991 equation has not been fully validated, the recommended weight limits derived from the revised equation are consistent with or lower than those generally reported in the literature. NIOSH believes that the revised 1991 lifting equation is more likely than the 1981 equation to protect most workers.
Workers' compensation claims associated with manual materials handling (MMH) represent the single largest source of claims and costs. Surprisingly, there have been few analyses of such losses associated with MMH. An examination of the nature of the injuries associated with MMH as well as the body parts most frequently affected can lead to a better understanding of the losses attributed to MMH to suggest further research efforts. A large sample of MMH claims was analysed and stratified with respect to body part affected and the nature of the injury. The outcome measures examined were frequency (number of claims) and severity (cost measures) of the claims. The analyses revealed that the lower back area and upper extremities were the body parts associated with approximately 70% of the claims. Strain was the nature of injury most frequently reported (51.3%). Lower back area strains were the most frequently reported nature of injury and body part combination. Additionally, an analysis of median claims costs revealed the occurrence of a small number of very expensive traumatic injuries.
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 approximately 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.
In the last three or four decades, studies of biomechanics have expanded from simple topical applications of elementary mechanics to entire areas of study. Studies and research in biomechanics now exceed those in basic mechanics itself, underlining the continuing and increasing importance of this area of study. With an emphasis on biodynamic modeling, Fundamentals of Biomechanics provides an accessible, basic understanding of the principles of biomechanics analyses. Following a brief introductory chapter, the book reviews gross human anatomy and basic terminology currently in use. It describes methods of analysis from elementary mathematics to elementary mechanics and goes on to fundamental concepts of the mechanics of materials. It then covers the modeling of biosystems and provides a brief overview of tissue biomechanics. The author then introduces the concepts of biodynamics and human body modeling, looking at the fundamentals of the kinematics, the kinetics, and the inertial properties of human body models. He supplies a more detailed analysis of kinematics, kinetics, and dynamics of these models and discusses the numerical procedures for solving the governing dynamical equations. The book concludes with a review of a few example applications of biodynamic models such as simple lifting, maneuvering in space, walking, swimming, and crash victim simulation. The inclusion of extensive lists of problems of varying difficulty, references, and an extensive bibliography add breadth and depth to the coverage. Focusing on biodynamic modeling to a degree not found in other texts, this book equips readers with the expertise in biomechanics they need for advanced studies, research, and employment in biomedical engineering.
Fatigue fracture of human lumbar vertebrae under cyclic axial compressive load has been investigated in vitro for load magnitudes between 20% and 70% of the ultimate compressive strength and cycle numbers between 1 and 5000. In addition, the dependence of the ultimate compressive strength of lumbar vertebrae on trabecular bone density and geometric dimensions was investigated. Seventy specimens of human lumbar motion segments were subjected to a fatigue test; 35 specimens were subjected to an ultimate strength test. The results state the probability of a lumbar vertebra encountering a fatigue fracture in relation to the magnitude of the cyclic load and the number of load cycles. In addition, it is shown that the ultimate compressive strength of a vertebra can be predicted with an error of less than 1 kN on the basis of bone density and endplate area.
It is widely believed that depalletizing operations in manufacturing and service environments sub- stantially increase the risk of occupationally related low back disorders (LBDs). It has been estab- lished that the weight of the box lifted off a pallet can affect the risk of occupationally related LBD but few have considered the influence of the location of the box on the pallet (region) when as- sessing risk. Thus, the objective of this study was to assess spinal loading characteristics and the probability of high LBD risk as a function of box weight and its location on the pallet. Ten expe- rienced order selectors were recruited from a local distribution center and were evaluated as they transferred boxes of different weights (40, 50, and 60 lb) from six different locations (regions) of a pallet to a pallet jack. Workers were monitored for their trunk motion characteristics as well as the electromyographic (EMG) activity of ten trunk muscles as they performed the task. Workplace factors as well as trunk kinematic and EMG information were used as inputs to: (1) a risk assess- ment model, and (2) an EMG-assisted model that was used to predict the three-dimensional spine loadings that occurred during the task. The results indicated that conditions where a worker must reach to a low level of the pallet increased spinal load and risk probability far more than changes in the weight of the box. Thus, spinal loads were significantly large in magnitude and would be ex- pected to lead to an increase in low back disorders when workers lifted form the lowest layer of the pallet. The load moment was found to be strongly influenced by pallet region, which resulted in increased spinal loading and risk probability as the moment increased. This effort has also facili- tated our understanding as to why spine loading increases under the various conditions studied in this experiment. Nearly all differences in spinal loading can be explained by a corresponding dif- ference in coactivation of the trunk musculature. This in turn significantly increases the synergistic forces supplied by each muscle to the spine and results in an increase in spinal loading. © 1997 John Wiley & Sons, Inc.
The clinical objective of the gait analysis laboratory, developed by United Technologies Corporation (Hartford, CT, USA) in 1980, at the Newington Children's Hospital is to provide quantified assessments of human locomotion which assist in the orthopaedic management of various pediatric gait pathologies. The motion measurement system utilizes a video-based data collection strategy similar to commercially available systems for motion data collection. Anatomically aligned, passive, retroreflective markers placed on the subject are illuminated, detected, and stored in dedicated camera hardware while data are acquired from force platforms and EMG transducers. Three-dimensional marker position information is used to determine: (i) the orientation of segmentally-embedded coordinate systems, (ii) instantaneous joint center locations, and (iii) joint angles. Joint kinetics, i.e., moments and powers, may also be computed if valid force plate data are collected.
A full set of governing dynamical equations for Hanavan's human body model are developed. The model consists of ellipsoids, elliptical cylinders, and frustrums of elliptical cones. It contains 34 degrees of freedom. The model is considered to be in an arbitrary force field and the limb motions may be either specified or left free. The governing equations then determine the internal limb moments (muscle forces), the limb displacements, and the displacement of the model itself in an inertial reference frame. An example motion representing the model response to an impulsive force loading is also presented.
A case-referent study was conducted in an automobile assembly plant to evaluate the health effect of trunk postures, such as bending and twisting, that deviate from anatomically neutral. Cases of back disorders were all those of workers who reported back pain to the medical department in a ten-month period and met the severity criteria of an interview. The referents were randomly selected workers free of back pain according to medical department records, an interview, and an examination. For each of the final 95 cases and 124 referents, the job was analyzed for postural and lifting requirements with a video recording and software analysis system by analysts blinded to the case/referent status. Back disorders were associated with mild trunk flexion [odds ratio (OR) 4.9, 95% confidence interval (95% CI) 1.4-17.4], severe trunk flexion (OR 5.7, 95% CI 1.6-20.4), and trunk twist or lateral bend (OR 5.9, 95% CI 1.6-21.4). The risk increased with exposure to multiple postures and increasing duration of exposure.
An epidemiologic case-control study undertaken in Connecticut during 1979-1981 indicated that persons with jobs requiring lifting objects of more than 11.3 kg (25 lb) an average of more than 25 times per day had over three times the risk for acute prolapsed lumbar intervertebral disc as people whose jobs did not involve lifting objects of this weight. If the body was usually twisted while the lifting was done, this elevation in risk was apparent with less frequent lifting. An especially high risk for prolapsed lumbar disc was associated with jobs involving lifting objects of more than 11.3 kg with the body usually twisted and the knees not bent while the lifting was done. Neither lifting objects of less than 11.3 kg nor twisting without lifting was associated with an increase in risk.
The purpose of this study was to determine the fatigue behaviour of human tendons in vitro. The testing was accomplished with the use of specially designed grips and the local measurement of tendon cross-sectional area. Ninety specimens prepared from Extensor digitorum longus (EDL) tendons of the foot were subjected to a cyclic square tension-tension stress waveform at physiological frequencies. The maximum tensile stress was normalised to values corresponding to prescribed levels between 10% and 90% of the calculated ultimate tensile strength (UTS) of 100 MPa. The minimum stress was set at 1% of the UTS. A replication of 10 specimens per stress level allowed the use of statistical models for the distribution of fatigue life. Results followed a linear model, of form S = 101.3 - 14.8 log(N), relating the normalised stress to the median number of cycles to failure, therefore suggesting the absence of an endurance limit. The Weibull distribution was found to describe adequately the probability of failure at each stress level. A model which takes into account in vivo healing was proposed. This model was able to explain the presence of intact tendons throughout the lifetime of an individual.
Estimates of spinal forces are quite sensitive to model assumptions, especially regarding antagonistic co-contraction. Optimization based models predict co-contraction to be absent, while electromyography (EMG) based models take co-contraction into account, but usually assume equal activation of deep and superficial parts of a muscle. The aim of the present study was to compare EMG based and optimization based estimates of spinal forces in a wide range of work tasks. Data obtained from ten subjects performing a total of 28 tasks were analysed with an EMG driven model and three optimization models, which were specifically designed to test the effects of the above assumptions. Estimates of peak spinal forces obtained using the different modelling approaches were similar for total muscle force and its compression component (on average EMG based predictions were 5% higher) and were closely related (R > 0.92), while differences in predictions of the peak shear component of muscle force were more substantial (with up to 39% lower estimates in optimization based models, R > 0.79). The results show that neither neglecting antagonistic co-contraction, nor assuming equal activation of deep and superficial muscles, has a major effect on estimates of spinal forces. The disparity between shear force predictions was due to an overestimation of activity of the lateral part of the internal oblique muscle by the optimization models, which is explained by the cost function preferentially recruiting larger muscles. This suggests that a penalty for active muscle mass should be included in the cost function used for predicting trunk muscle recruitment.
Intervention research for prevention of occupational low back injuries has focused on the effects of reducing extreme torso flexion and the external moment. Little is known about prevention strategies for torso twisting and lateral bending. The objective of this study was to assess the effect of pallet distance with regard to a constant lift origin on the torso kinematics and a measure of low back disorder risk. Fifteen male participants transferred 11.3 kg boxes from a constant origin to six different regions on a pallet. Two pallet distances with regard to the lift origin were investigated. ANOVA indicated that increasing the pallet distance resulted in increases in torso kinematics (velocities and accelerations) as well as a measure of risk of low back disorder. The increases in torso kinematics (e.g. twisting and lateral awkward postures and bending velocities) occurred mostly at the lower height regions on the pallet. It is concluded that increasing the pallet distance with regard to the lifting origin, with the intention to influence the participant to take a step during a palletizing task does not appear to be an effective intervention strategy to reduce the risk of low back disorder associated with torso kinematics.
Spine loads associated with lifting a 9-kg weight were estimated at three torso flexion angles (0 degrees, 22.5 degrees, and 45 degrees), and lumbosacral motion segments were cyclically loaded using these loads until failure or to a maximum of 10,020 cycles.
To simulate the postures and loads experienced by the lumbar spine during repetitive lifting of moderate weights in different torso flexion postures, and to analyze the fatigue failure response of lumbosacral motion segments.
Previous fatigue failure studies of lumbar motion segments have not reproduced the combination of spinal postures, loads, and load rates anticipated in different torso flexion postures during lifting tasks characteristic of those in occupational settings.
Twelve fresh human lumbosacral spines were dissected into three motion segments each (L1-L2, L3-L4, and L5-S1). Motion segments within each spine were randomly assigned to a simulated torso flexion angle (0 degrees, 22.5 degrees, or 45 degrees) using a partially balanced incomplete block experimental design. Spinal load and load rate were determined for each torso flexion angle using previously collected data from an EMG-assisted biomechanical model. Motion segments were creep loaded for 15 minutes, then cyclically loaded at 0.33 Hz. Fatigue life was taken as the number of cycles to failure (10 mm displacement after creep loading). Specimens were inspected to determine failure mechanisms.
The degree of torso flexion had a dramatic impact on cycles to failure. Motion segments experiencing the 0 degrees torso flexion condition averaged 8,253 cycles to failure (+/-2,895), while the 22.5 degrees torso flexion angle averaged 3,257 (+/-4,443) cycles to failure, and motion segments at the 45 degrees torso flexion angle lasted only 263 cycles (+/-646), on average. The difference was significant at P < 0.0001, and torso flexion accounted for 50% of the total variance in cycles to failure.
Fatigue failure of spinal tissues can occur rapidly when the torso is fully flexed during occupational lifting tasks; however, many thousands of cycles can be tolerated in a neutral posture. Future lifting recommendations should be sensitive to rapid development of fatigue failure in torso flexion.
Survival analysis techniques were used to compare the fatigue failure responses of elderly motion segments to a middle-aged sample.
To compare fatigue life of a middle-aged sample of lumbosacral motion segments to a previously tested elderly cohort. An additional objective was to evaluate the influence of bone mineral content on cycles to failure.
A previous investigation evaluated fatigue failure responses of 36 elderly lumbosacral motion segments (average age, 81 +/- 8 years) subjected to spinal loads estimated when lifting a 9-kg load in 3 torso flexion angles (0 degrees, 22.5 degrees, and 45 degrees). Results demonstrated rapid fatigue failure with increased torso flexion; however, a key limitation of this study was the old age of the specimens.
Each lumbosacral spine was dissected into 3 motion segments (L1-L2, L3-L4, and L5-S1). Motion segments within each spine were randomly assigned to a spinal loading condition corresponding to lifting 9 kg in 3 torso flexion angles (0 degrees, 22.5 degrees, or 45 degrees). Motion segments were statically loaded and allowed to creep for 15 minutes, then cyclically loaded at 0.33 Hz. Fatigue life was taken as the number of cycles to failure (10 mm displacement after creep loading).
Compared with the older sample of spines, the middle-aged sample exhibited increased fatigue life (cycles to failure) in all the torso flexion conditions. Increased fatigue life of the middle-aged specimens was associated with the increased bone mineral content (BMC) in younger motion segments (mean +/- SD, 30.7 +/- 11.1 g per motion segment vs. 27.8 +/- 9.4 g). Increasing bone mineral content had a protective influence with each additional gram increasing survival times by approximately 12%.
Younger motion segments survive considerably longer when exposed to similar spine loading conditions that simulate repetitive lifting in neutral and flexed torso postures, primarily associated with the increased bone mineral content possessed by younger motion segments. Cycles to failure of young specimens at 22.5 degrees flexion were similar to that of older specimens at 0 degrees flexion, and survivorship of young specimens at 45 degrees flexion was similar to the older cohort at 22.5 degrees.
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