Article

Effect of forklift operation on lower back pain: An evidence‐based approach

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Abstract

Most studies on the occupational hazards associated with forklift operation have examined risks of fatalities and traumatic injuries. Few studies have examined the magnitude of risk of lower back pain. This research deals with an evidence-based approach designed to examine if there is a relationship between whole-body vibration and driver postures with lower back pain among forklift operators and to offer some recommendations to minimize the risk of lower back pain. To accomplish the study goal, an evidence-based approach was adopted from evidence-based medicine. The basic steps of this evidence-based approach were: (1) formulation of a clear research question from a worker-occupational problem; (2) search of the literature for the best evidence with which to answer the question; (3) critically appraise the evidence; and (4) implement useful findings in occupational health and safety practices. In addition, the metarelative risk was calculated and the biological plausibility between whole body vibration (WBV) and operator posture with lower back pain was investigated. Six observational articles satisfied the inclusion criteria adopted in this research. The methodological qualities of the published studies ranged from marginal to average. The metarelative risk was 2.1, indicating that operators exposed to driving forklifts are greater than twice the risk of those not exposed to driving forklifts to experience lower back pain. There are biological mechanisms by which WBV and operator postures could develop lower back pain. Some aspects of the work environment that influenced vibration are seat, speed, track, and tires. Awkward postures and static postures are affected by cab design, seat, time spent seated, and the task performed. It appears that there is a causal relationship between forklift operation and lower back pain. The evidence examined shows a strong association and consistency between all studies and this relationship is biologically plausible. It is recommended that intervention studies be conducted to determine the effectiveness of ergonomic controls. © 2008 Wiley Periodicals, Inc.

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... Forklifts are commonly used in industrial supply chains, where transport of heavy goods and loads lifting are involved. Those vehicles are responsible for traumatic accidents and musculoskeletal disorders (MSDs) for the forklift driver [1][2][3]. ...
... Some of the risk factors of MSDs for those individuals are repetitive trunk twisting, sideways trunk bending and rotation, exposure to whole-body vibrations [1,[3][4][5][6], neck flexion and rotation, especially during reverse driving [3,7], neck extension without support, and static sitting positions [8]. ...
... Some of the risk factors of MSDs for those individuals are repetitive trunk twisting, sideways trunk bending and rotation, exposure to whole-body vibrations [1,[3][4][5][6], neck flexion and rotation, especially during reverse driving [3,7], neck extension without support, and static sitting positions [8]. ...
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Forklifts are commonly used in industrial supply chains to transport heavy loads. Forklift drivers have the risk of developing musculoskeletal discomfort derived from the movement pattern required at work. This research aimed to investigate the spinal range of motion (ROM) and musculoskeletal discomfort of forklift drivers and compare it with a control group. Forklift drivers (39 males) and office workers (31 males) were recruited to assess cervical, thoracic, and lumbar ROM with an electronic double inclinometer. Additionally, musculoskeletal discomfort was registered with the Cornell Discomfort Musculoskeletal Questionnaire. Forklift drivers showed a higher cervical discomfort and ROM of lateral lumbar bending than office workers. Both groups reported lower ROM in cervical and lumbar lateral bending on the right side versus the left side. No differences of asymmetry were reported for any variable between groups. Specific exercise programs may correct these mobility imbalances.
... Some of the health hazards contributing to lower back pain are exposure to whole body vibration, and awkward postures including static sitting, trunk twisting and bending, neck flexion and rotation. [1,4] Reach trucks, also known as narrow aisle trucks, are small forklifts used to lift and transport pallets of materials, and are typically used in warehouses or distribution centers. Reach trucks (Figure 1) move in a direction lateral to the natural seated posture of the operator. ...
... There are a number of design factors and ergonomic recommendations for optimization of a forklift seat and therefore minimized strains ranging from discomfort and fatigue to pain and musculoskeletal disorders. For instance presence of an armrest and a tilting backrest support the arm and upper body, and carry a part of the arm and upper body weight which results into reduced lumbar disc pressure [1]. This is only possible if the operators make use of the back rest appropriately. ...
... A list of ergonomic properties and adjustable features of the cabin is provided in table 1. These features result in minimizing awkward postures during extended periods of sitting [1]. ...
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The task of handling reach trucks frequently involves poor working postures. The location of the steering wheel in most reach trucks is in front of the operator which requires the drivers to bend forward and stretch their hands for holding onto the steering wheel. To overcome visibility restrictions, this posture is aggravated by twisting and bending their torso sideways. This paper presents a usability study which was conducted to compare adoption of ergonomic features in a new reach truck cabin with the way they were intended to be employed for improving physical working conditions. Participants drove the reach truck on a test track performing tasks of varying complexity. Video recordings were utilized to facilitate the observations. The results indicate that improved ergonomics features of the reach truck are not used as intended. The test subjects instead adopted postures that they were accustomed to when driving common reach trucks. The possible contributing factors to this posture regression are discussed. The procedure used in this study is recommended for the companies to determine the effectiveness and adoption of ergonomics solutions.
... Forklift truck operators are subjects of many ergonomic analysis due to high physical and psychological requirements of their work [1], [2], [3], [4]. This job is related with reasonably high risk of musculoskeletal disorders (MSD), particularly those involving spine. ...
... The reasons are operator postures and additionnally whole body vibration (WBV). Awkward operator's postures as well as static workload are affected by cab design, seat, time spent seated, and the task performed [2]. The vibrations level is influenced by work factors like seat, speed, track, and tires. ...
... They therefore reviewed several studies of forklift driving in cold temperatures, whole body vibration and postural loads to assess the risk of lower back pain. Similarly, Viruet, Genaidy, Shell, Salem, and Karwowski (2008) investigated the effect of forklift operation on lower back pain. They found that equipment such as the seat, speed, floor surface, tires, together with awkward, static postures were affected by the time spent seated and the task that was being performed. ...
... As Horberry et al. (2004) point out, forklift safety cannot be achieved only by forklift design and driver training -work and the working environment are also important. From this point of view, data were collected not only from inside the cabin, but also from the work environment and working conditions through observations and measurements Among the effects of cabin conditions, vibration and poor body postures have been highlighted (Motmans, 2012;Viruet et al., 2008). Similarly, in the present study, lower back discomfort had a high risk score, and neck disorders were emphasized by drivers as a consequence of visual difficulties. ...
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Évaluer les facteurs de risques professionnels des conducteurs de chariots élévateurs The use of materials handling equipment is inevitable in a rapidly-growing supply chain to move diverse types of sub/products. Forklifts are one of the best known and widely used pieces of equipment in almost any industry, but especially in warehouses and shipping departments. Moving the right amount of the right materials safely and in a timely manner is often believed to be related to the forklift driver’s experience. Although it is proven that forklift design may affect the performance a forklift driver, environmental and cognitive factors have not been studied in detail. This study aims to consider related factors to improve occupational health and safety for forklift drivers. A survey was designed to gather personal information about drivers, their comfort level regarding environmental factors, and their comments on forklift design and usability. Environmental factors were measured with an environmental meter and drivers were asked to complete the Cornell Musculoskeletal Discomfort Questionnaire. A mobile eye tracker was used to gather and assess fixation data and change in pupil size as indicators of cognitive load in pallet handling duties. An ANOVA analysis highlighted the importance of considering the combination of factors and asking drivers’ opinions in real-life applications.
... The promotion and maintenance of good occupational ergonomics reduces the risk of chronic injuries and illnesses, and consequently decreases the cost incurred by lost productivity, sick leave, and medical care (Kok et al., 2020). Forklift driving in industry is one of the work tasks linked to increased risk of upper body problems (Flodin et al., 2018;Viruet et al., 2008). The risk factors are commonly identified and managed using observational methods based on direct on-site observation or watching recorded videos of workers performing their usual tasks. ...
Conference Paper
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Observational postural assessment methods which are commonly used in industry are time consuming and have issues of inter- and intra-rater reliability. Computer vision (CV) based methods have been proposed, but they have mainly been tested inside lab environments. This study aims to develop and evaluate an upper body postural assessment system in a real industry environment using a single depth camera and OpenPose for the task of forklift driving. The results were compared with XSens, an Inertial Measurement Unit (IMU) based system. Data from three forklift drivers performing seven indoor and outdoor tasks were recorded with a depth camera and XSens sensors. The data were then analyzed with OpenPose with additional custom processing. The angles calculated by the computer vision system showed small errors compared to the XSens system and generally followed the trend of the XSens system joint angle values. However, the results after applying ergonomic thresholds were vastly different and the two systems rarely agreed. These findings suggest that the CV system needs further study to improve the robustness on self-occlusion and angle calculations. Also, XSens needs further study to assess its consistency and reliability in industrial environments.
... How proficient driver is connected with MSDs is maintained by epidemiological examinations among drivers in different kinds of vehicles. These join carriers, country June 1, 2021 Case study on Ergonomics carriers [3], forklift drivers [4] [5] transport drivers [6], and taxi drivers [7]. A study also examines the drivers between Cab, bus, and truck drivers about postural study in respect to musculoskeletal discomforts [8]. ...
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Ergonomics coordinates information from the human sciences to coordinate with occupations, frameworks, items, and conditions to the physical and mental capacities and impediments of individuals Musculoskeletal disputes (MSD) impact the staffs in various professions including vehicle drivers. The assessments happening strong issues from the truck, taxi, and transport drivers endeavored at this point there is no examination to evaluate these three auto clients and give ergonomic obstructions among them. In such a way, the examination intends to study the degree of musculoskeletal issues on basic components impacting the three vehicles concerning segment shapes and endeavors drivers' machines. It furthermore intends to assess the level of musculoskeletal sufferings of actual parts of vehicle drivers from the standard factors, and recommend ergonomic helps to address the recurrence of musculoskeletal issues among the drivers. Assessment on the issues of these vehicle drivers using RULA and CMDQ have endeavored. The results showed that there was a connection between the body bits of truck and bus drivers on the RULA and CMDQ regards. The vehicle drivers showed that their neck, second rate back, subordinate legs, upper appendage, and wrists were the primary five biggest normal body parts related to musculoskeletal issues. Accordingly, the examination proposes proposed ergonomics obstructions needed for these body divides.
... How proficient driver is connected with MSDs is maintained by epidemiological examinations among drivers in different kinds of vehicles. These join carriers, country carriers [3], forklift drivers [4] [5] transport drivers [6], and taxi drivers [7]. Park S J takes contrasted real seating solace position and respect to ideas in the investigation. ...
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Musculoskeletal problems (MSD) influence the staffs in numerous professions including vehicle drivers. The examinations happening muscular issues from truck, taxi, and bus drivers were attempted yet there is no investigation to assess these three automobile users and give ergonomic interferences amongst them. In such manner, the study means to survey the level of musculoskeletal problems on critical elements influencing the three automobiles as for demographic contours and undertakings drivers’ appliance. It additionally means to evaluate the degree of musculoskeletal sufferings of physical portions of automobile drivers from the usual factors, and suggest ergonomic facilitations to address frequency of musculoskeletal problems among the drivers. Evaluation on the issues of these vehicle drivers utilizing RULA and CMDQ were attempted. The outcomes exhibited that there was a correlation on the body portions of truck, taxi and bus drivers on the RULA and CMDQ esteems. The vehicle drivers showed that their neck, inferior back, subordinate legs, upper limb and wrists were the main five greatest usual body parts associated with musculoskeletal issues. As such, the study proposes proposed ergonomics interferences required for these body portions.
... Vibration originates from different sources are transmitted to the pelvis and back along the vertical axis via the base and back of the seat [14,15,16,17,18,19]. On the other hand, the pedals and steering handle transmit additional vibrations to the feet and hands of the rider. ...
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T wo-wheel motorcycles are preferred in many countries as they have some merits such as cheaper, easy to handle and give higher fuel economy compared to three and four-wheel vehicles. Majority of the population in India falls under low and middle-income groups. Two-wheelers cater to the needs of low and middle-income users, and fill the gaps when public transport systems are inefficient or not available. Most of the people in India use motorcycles for transportation. However, due to different road conditions, motorcycle rider experiences different health effects within a few years of their vehicle travel. This paper investigates the effect of vibration on a man commuter's health. For this purpose, a mathematical model of a male rider's body was considered, and a numerical analysis was carried out to assess the effect of vibration acting on the commuter during a two-wheeler ride under various road conditions for a chosen suspension system and presented in this paper. Road conditions were chosen based on the different surface roughness values. The most affected rider's body part due to the vibration of the two-wheeler was determined from the results. The results presented in this paper can be useful in understanding the vibrations induced in the human body while riding a two-wheeler at a particular velocity on a specific road surface.
... The ergonomic factors that potentially contribute to back pain in the agricultural sector are poor posture while driving, sitting for long periods without being able to change position, poorly placed machine controls that require the driver to twist or stretch, poor visibility of the operation (which requires twisting or stretching to get an adequate view), manual lifting and carrying of heavy or awkward loads, and repeatedly climbing into or out of a high or difficult-toaccess cab. The risk increases when the driver is exposed to one or more of these factors while being subjected at the same time to whole-body vibration (Barriera-Viruet, 2008;HSE, 2005). ...
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Professional drivers have been found to be at a high risk of developing low back pain due to prolonged sitting and vehicle vibration. In a previous survey carried out on 1,155 tractor drivers, tractor vibration and/or incorrect posture while driving were found to cause low back disorders in more than 80% of the interviewed drivers. In this context, the present research introduces a new evaluation protocol to assess the ergonomic characteristics of agricultural tractor seats through the use of pressure sensors, taking into account both static and dynamic conditions. The degree of comfort was defined by analyzing the pressure distribution exerted by a sample of 12 drivers sitting on two seats in five different operating conditions. The pressure distribution values thus obtained were compared with the corresponding pressures recorded with the 12 drivers sitting on a reference seat (rigid seat, backrest, and suspension) designed for the purpose. From the comparison, it was possible to define a comfort index (CI) that allowed an objective assessment of the two seats. Statistical analysis showed that the CIs of the two seats were significantly different in all five operating conditions. Moreover, the two seats showed different CIs as a function of the operating condition. Although less comfortable, one seat showed almost constant CI values in all five operating conditions. Conversely, the other seat showed a progressively decreasing CI from the static condition to the uneven ground condition. Keywords: Comfort index, Occupational diseases, Pressure distribution, Safety.
... Lower back disorders have been significantly associated with heavy machinery operating tasks because of the biological mechanisms arising from WBV exposure and wrong postures which, in turn, are related to workplace characteristics and use, like the kind of seat, operating speed, track or tyres, cab design, the amount of time spent while seated, and the task performed [23]. ...
Article
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Operator exposure to high levels of whole-body vibration (WBV) presents risks to health and safety and it is reported to worsen or even cause back injuries. Work activities resulting in operator exposure to whole-body vibration have a common onset in off-road work such as farming. Despite the wide variability of agricultural surface profiles, studies have shown that with changing soil profile and tractor speed, the accelerations resulting from ground input present similar spectral trends. While on the one hand such studies confirmed that tractor WBV emission levels are very dependent upon the nature of the operation performed, on the other, irrespective of the wide range of conditions characterizing agricultural operations, they led researchers to set up a possible and realistic simplification and standardization of tractor driver comfort testing activities. The studies presented herewith indicate the usefulness, and the possibility, of developing simplified procedures to determine agricultural tractor vibration comfort. The results obtained could be used effectively to compare tractors of the same category or a given tractor when equipped with different seats, suspension, tyres, etc.
... However, the relationship cannot be rejected, and the proposed mechanism has high biological plausibility. 82 As in the present reviews, prior reviews agree that the primary limitation stems from a lack of published prospective studies with high-quality exposure measurement approaches. ...
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Introduction: Low back disorders (LBDs) are the most common musculoskeletal problem among farmers, with higher prevalence rates than in other occupations. Farmers who operate tractors and other types of machinery can have substantial exposure to whole body vibration (WBV). Although there appears to be an association between LBDs and WBV, the causal relationship is not clear. Objective: This scoping review investigates the association between whole body vibration (WBV) and low back disorders (LBDs) specifically among farmers. Methods: Nine databases were searched using groups of terms for two concepts: 'farming' and 'low back disorder'. Screening, data extraction and quality assessment were performed by two reviewers independently. Included studies met the following criteria: focused on adult farmers/agricultural workers; assessed exposure to operating farm machinery such tractor, combine, or all-terrain vehicle; assessed LBDs as an outcome; and reported an inferential test to assess the relationship between WBV and LBD. Results: After 276 full texts screened, 11 articles were found to analyze WBV as a risk factor for LBDs. Three were case-control, five cross-sectional and three retrospective cohorts. Four studies showed no association between WBV and LBDs, four a positive association and three results were mixed depending on the exposure/outcome measure. Conclusion: A firm conclusion is difficult due to heterogeneity in, LBDs definition, type of farm commodity, study design, and statistical strategy. Direct comparisons and synthesis were not possible. Although retrospective cohort studies tended to show a relationship, future studies with a prospective cohort design could help clarify this association further.
... ve rating schemes. According to Palmer et al. (2002), the vibration is blamed as one important occupational risk in the industry, and is also directly linked to the incidence of back-pain in professional drivers. Besides, the use of motorised vehicles, when correlated to human back problems, seems to be the primary agent (White and Panjabi., 1990). Viruet et al. (2008) show an evidence-based approach designed to examine if there is a relationship between whole-body vibration and driver postures with lower back pain among forklift operators. They conclude that there is a strong association and consistency between all the studies. Velmurugan et al. (2011) studied the mechanical whole-body vibration in t ...
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The production and use of ride vehicles have grown in recent decades. Back-pain has been associated with the prolonged use of several types of vehicles and the vibration reported as the main cause. This paper aims at determining the degree of driver's comfort and safety related to vibration in ride vehicles. Experimental measurements in four vehicles of the same category are performed. Comparisons based on type of pavement and car speeds are used as a basis for analysis in each case. The whole body vibration (WBV) and hand-arm vibration (HAV) are measured using accelerometers placed at contact parts of the driver-vehicle interface and on the steering wheel. Trends in the comfort levels could be statistically observed in the analysed cars based on the acquired data. It was also possible to infer about the potential harm for certain conditions where vibration levels may exceed standard exposure limits.
... A relation has been documented between the position and velocities of the arm and disorders in the neck and shoulder region due to neck/shoulder strain and demanding visual perception (Eklund et al., 1994; Wiholm et al., 2007; Helland et al., 2008; Choi et al., 2009). Awkward postures and static postures are affected by cab design, seat, time spent seated, and the task performed (Barriera Viruet et al., 2008). Important aspects of forklift driving are the steering wheel and the driving performance (Davis et al., 2008 ). ...
Article
The aim of this study was to evaluate the consequences on the physical workload of new solutions in the forklift cab environment for the driver by quantifying the physical workload on the neck, shoulders, arms and wrists as an effect of steering systems. Twelve male subjects conducted identical test cycles with three types of steering: normal, tilted and miniature. The physical load on the drivers was evaluated using goniometry, inclinometry and electromyography. No major differences were detected when comparing the normal to the tilted steering wheel. The miniature steering wheel showed, in comparison to the normal steering wheel, lower velocity for the right and left wrists, lower elevation and lower velocity for the left upper arm, a reduction in load on the right trapezius muscle, respectively, and most noticeably a 6-fold increase in the “static” load and a 10-fold decrease in the time for rest/recovery for the left wrist extensor muscles. The tilted steering wheel did not have any significant effect on the workload. However, the effects of the miniature steering wheel indicate an increased risk for over exertion resulting in disorders of the wrist and forearm for the left side.Relevance to industryWhen introducing new techniques or changes in technical systems, it is essential to evaluate the effects on the human workload with objective measurements.
Chapter
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Doctors within the NHS are confronting major changes at work. While we endeavour to improve the quality of health care, junior doctors' hours have been reduced and the emphasis on continuing medical education has increased. We are confronted by a growing body of information, much of it invalid or irrelevant to clinical practice. This article discusses evidence based medicine, a process of turning clinical problems into questions and then systematically locating, appraising, and using contemporaneous research findings as the basis for clinical decisions. The computerisation of bibliographies and the development of software that permits the rapid location of relevant evidence have made it easier for busy clinicians to make best use of the published literature. Critical appraisal can be used to determine the validity and applicability of the evidence, which is then used to inform clinical decisions. Evidence based medicine can be taught to, and practised by, clinicians at all levels of seniority and can be used to close the gulf between good clinical research and clinical practice. In addition it can help to promote self directed learning and teamwork and produce faster and better doctors
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The vibration in 100 different vehicles has been measured, evaluated and assessed according to British Standard BS 6841 (1987) and International Standard ISO 2631 (1997). Vibration was measured in 14 categories of vehicle including cars, lift trucks, tractors, lorries, vans and buses. In each vehicle, the vibration was measured in five axes: vertical vibration beneath the seat, fore-and-aft, lateral and vertical vibration on the seat pan and fore-and-aft vibration at the backrest. The alternative methods of evaluating the vibration (use of different frequency weightings, different averaging methods, the inclusion of different axes, vibration dose values and equivalent r.m.s. acceleration) as defined in the standards have been compared. BS 6841 (1987) suggests that an equivalent acceleration magnitude is calculated using vibration measured at four locations around the seat (x -, y -, z -seat and x -backrest); ISO 2631 (1997) suggests that vibration is measured in the three translational axes only on the seat pan but only the axis with the most severe vibration is used to assess vibration severity. Assessments made using the procedure defined in ISO 2631 tend to underestimate any risks from exposure to whole-body vibration compared to an evaluation made using the guidelines specified in BS 6841; the measurements indicated that the 17 m/s1.75 “health guidance caution zone” in ISO 2631 was less likely to be exceeded than the 15 m/s1.75 “action level” in BS 6841. Consequently, ISO 2631 “allows” appreciably longer daily exposures to whole-body vibration than BS 6841.
Article
Acute effects on drivers from different twisted postures and whole-body vibrations were studied. Effect variables were subjective discomfort and EMG-activity. The study was performed with experienced drivers on test tracks in the field. Two types of industrial trucks and an agricultural tractor were used. The machines gave different types of vibrations.Ratings of discomfort with Borg's CR-10 scale and EMG-activity correlated well with both the degree of twist of the posture and the vibration level. The discomfort was exclusively localised to the lumbar and the neck-shoulder regions. It was foremost expressed as a feeling of tension and common discomfort. Rotation of the neck, 30–50 degrees, gave big effects on both discomfort and EMG-level. No clear differences between the effects of the vibration exposures from the different vehicles were found.
Article
The vibration isolation efficiency of seating has been evaluated in 100 work vehicles in 14 categories (cars, vans, lift trucks, lorries, tractors, buses, dumpers, excavators, helicopters, armoured vehicles, mobile cranes, grass rollers, mowers and milk floats). Seat isolation efficiency, expressed by the SEAT value, was determined for all seats (67 conventional seats and 33 suspension seats) from the vertical acceleration measured on the floors and on the seats of the vehicles. For most categories of vehicle, the average SEAT value was less than 100%, indicating that the average seat provided some attenuation of vibration. However, there were large variations in SEAT values between vehicles within categories. Two alternative vibration frequency weightings (Wb from BS 6841, 1987; Wk from ISO 2631, 1997) yielded SEAT values that differed by less than 6%. Overall, the SEAT values determined by two alternative methods (the ratio of r.m.s. values and the ratio of vibration dose values) differed by less than 4.5% when using weighting Wb, although larger differences may be expected in some situations. The median SEAT value for the suspension seats was 84.6% the median SEAT value for the conventional seats was 86.9% (based on weighting Wb and the ratio of r.m.s. values). Predicted SEAT values were obtained assuming that each seat could be interchanged between vehicles without altering its transmissibility. The calculations suggest that 94% of the vehicles investigated might benefit from changing the current seat to a seat from one of the other vehicles investigated. Although the predictions are based on assumptions that will not always apply, it is concluded that the severity of whole-body vibration exposures in many work environments can be lessened by improvements to seating dynamics. . All rights reserved.
Article
Vehicle manufacturers are continuously seeking to improve vibration comfort. In this paper, subjective responses from transient vibrations in a forklift were analyzed on the basis of ISO 2631-1 and a number of additional variables. The objectives were to define: the effect of different operating conditions and appropriate background variables of subjects on perceived motions; the development of model that describes perceived discomfort as a function of measured vibrations; and important frequencies for prediction of vibration discomfort. The experiment was based on 12 different operating conditions defined by the variables: vehicle speed, obstacle height and load conditions. Eleven professional drivers participated and their responses of overall discomfort were defined by a vector sum of three perceived motions: shaking, for-aft and up-down motions. The evaluation method, maximum transient vibration value as defined in ISO 2631-1 was found to be adequate in predicting vibration discomfort during a four second transient vibration exposure. By analysis of narrow frequency band spectra of vibrations several explanations for the test results are discussed. The best results were obtained using a prediction model based on accelerations in 13-octave bands of pitch vibrations.
Article
In order to determine the influence of some parameters of a forklift such as the road profile, the tyre characteristics, the riding comfort, etc., measurements carried out on a forklift with different tyres and seats were evaluated using different standards and methods. In addition, a simulation model was developed and used to investigate the influence of these parameters. Simulations and test run results showed good agreement.The comparison of the results obtained with several methods of comfort evaluation and a series of tests showed that they nearly all resulted in the same classification. However, the results obtained with different methods could not always be compared among themselves.Solid tyres were found to be more comfortable than pneumatic ones because of their high damping. The negative influence of higher stiffness was smaller than the positive influence of higher damping. The simulations pointed out that for a global general investigation about comfort, the influence of the horizontal tyre stiffness and damping can be neglected. Also the seat characteristics could be linearized. When the stability of the forklift has to be investigated, the horizontal forces must also be considered.
Article
Many vibrational environments also subject the worker to awkward, asymmetric and prolonged postures. This paper reviews the epidemiological, biomechanical and physiological factors involved in working postures which could lead to musculoskeletal problems. Too little or too much sitting leads to low back pain. Sedentary postures, including driving, also lead to a higher risk of a herniated disc. In sitting the pelvis rotates and higher pressures exist in the disk. A backrest inclined to 110° or more and with a lumbar support will reduce the disk pressure. Jobs involving excessive force application will be more apt to cause muscular and ligamentous damage. However, these excessive demands can occur in whole body vibration environments too. Neck, shoulder and arm problems are usually related to posture but can occur in WBV environments. Knee problems, in the standing worker, may be due to a flexed knee posture in an attempt to attenuate vibrations. Excessive postural demands on the neck, shoulder and arm will lead to higher muscle forces and higher joint forces. Recommendations are given to reduce risk of disability.
Article
This investigation was designed as a rapid review of available knowledge on high acceleration events in practice. The aim was to consider if the risks associated with regular exposure justify further investigation of the problem. Three linked investigations were carried out: to gather published information, to gather expert opinion, and to analyse available vehicle records. The literature showed that although no fully acceptable epidemiological data are available, exposure to high levels of vibration and shock provably increases the risk of back problems. Experts considered high acceleration events important as regards the health of drivers of certain vehicles. They thought that more research into the effects on health is needed but comfort and epidemiological investigations have some severe practical drawbacks as well as advantages. More biodynamic research is needed to engender plausible hypotheses on the effects on health before consideration of further epidemiological research and generation of dose-response relationships. Vehicle measurements confirmed information from the literature that BS6841 [1]Wbweighted r.m.s. values over 4 s of up to 5·6 m/s2and unweighted peak values of at least 20 m/s2occur withWbweighted peak values of up to 15 m/s2and sometimes nearly 30 m/s2. Daily Vibration Dose Values of the order of 20 ms−1·75are quite probable. Measured accelerations suggested some common features of high acceleration events. Many are of an oscillatory nature with frequencies of the order of 2–3 Hz, whilst large magnitude transient accelerations of the order of 25–20 ms duration also occur in certain situations. The long term weighted r.m.s. value does not reflect the presence of high acceleration events that occur once every few minutes and may underestimate the health risk.
Article
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Article
The purpose of this study was to examine the three-dimensional low back loads, spinal motions, and trunk muscular activity during gait. Specific objectives involved assessment of the effects of walking speed, and arm swing on spinal loads, lumbar spine motion, and muscular activation. An in vivo modeling experiment using five male participants. Thirty walking trials were performed by each participant yielding five repeats of each condition (3 walking cadences x 2 arm swing conditions). Walking is often prescribed as a rehabilitation task for individuals with low back injuries. However, there are few studies which have examined the joint loading, spinal motions, and muscular activity present when walking. Additionally, the majority of studies examining spine loading during gait have used an inverse dynamics model, commencing at the cranial aspect of the body, approach which does not include the impulsive phases of gait (i.e. heel strikes and toe offs). Low back joint forces (bone on bone) and moments were determined using an anatomically complex three-dimensional model (detailing 54 muscles and the passive structures acting at the low back) during three walking cadences and with free arm swing or restricted arm swing. In order to assess the influence of the transient factors such as heel contact on the joint forces a bottom up (from the feet to the lumbar spine) rigid link segment analyses approach was used as one input to the three-dimensional anatomic model. Lumbar spine motion and trunk muscle activation levels were also recorded to assist in partitioning forces amongst the active and passive tissues of the low back. Net joint anterior-posterior shear loading was the only variable significantly affected by walking cadence (fast versus slow P < 0.0003). No variable was significantly affected by the arm swing condition. Trends demonstrated an increase in all variables with increased walking cadence. Similarly, most variables, with the exception of axial twist and lateral bend lumbar spine motion and lateral joint shear, demonstrated increasing trends caused by the restriction of normal arm swing. Tissue loading during walking appears to be below levels caused by many specific rehabilitation tasks, suggesting that walking is a wise choice for general back exercise and rehabilitation programs. Slow walking with restricted arm swing produced more 'static' lumbar spine loading and motion patterns, which could be detrimental for certain injuries and tissues. Fast walking produced a more cyclic loading pattern.
Article
The investigators describe their multifaceted approach to the study of the relationship between whole-body vibration and low back pain.In vitroexperiments, using percutaneous pin-mounted accelerometers have shown that the natural frequency is at 4·5 Hz. The frequency response was affected by posture, seating, and seat-back inclination. The response appears to be largely determined by the rocking of the pelvis. Electromyographic studies have shown that muscle fatigue occurs under whole body vibration. After whole body vibration exposure the muscle response to a sudden load has greater latency. Vehicle driving may be a reason for low back pain or herniated nucleus pulposus. Prolonged seating exposure, coupled with the whole body vibration should be reduced for those recovering from these problems. Vibration attenuating seats, and correct ergonomic layout of the cabs may reduce the risks of recurrence.
Article
Operator field of view is of primary importance for ergonomic, efficient and safe operation of field machines such as tractors, forest harvesting machines, and earthmoving equipment. This paper describes a technique that could be used for an objective assessment of operator cabin features that degrade the field of view.
Article
A large number of studies have been conducted and researchers have suggested several criteria for evaluating discomfort and the suitability of a tractor seat in a given working condition. The studies have led to various parameters, viz. the body pressure distributed under and supporting both the buttocks, thighs and the back of an operator, control of posture in static or dynamic condition, ride vibration, exposure time on task and other factors. But in the absence of a more definitive and the most logical criteria particularly from biomechanical viewpoint, the researchers will continue to design conditions and procedures to understand the seat dynamics and evaluate the seating discomfort. Therefore, this paper reviews the research information available in this regard and attempts to set the most appropriate procedure for assessment of seating discomfort during tractor driving.Relevance to industryThis paper attempts to project the most appropriate method of assessment and selection of tractor seats from engineering and biomechanical view point which could be adopted by the tractor seat manufacturers. It is designed to enhance the feeling of comfort, safety, convenience, and results in higher work output from the operator.
Article
Engineering solutions to minimize the effects on operators of vibrating mobile machinery can be conveniently grouped into three areas: •Reduction of vibration at source by improvement of the quality of terrain, careful selection of vehicle or machine, correct loading, proper maintenance, etc.•Reduction of vibration transmission by incorporating suspension systems (tyres, vehicle suspensions, suspension cab and seat) between the operator and the source of vibration.•Improvement of cab ergonomics and seat profiles to optimize operator posture. These paper reviews the different techniques and problems linked to categories (2) and (3). According to epidemiological studies, the main health risk with whole-body vibration exposure would appear to be lower back pain. When designing new mobile machinery, all factors which may contribute to back injury should be considered in order to reduce risk. For example, optimized seat suspension is useless if the suspension seat cannot be correctly and easily adjusted to the driver's weight or if the driver is forced to drive in a bent position to avoid his head striking the ceiling due to the spatial requirement of the suspension seat.
Article
The occurrence of several types of low back pain (LBP) was investigated by a standardized questionnaire in a group of 219 port machinery operators exposed to whole-body vibration (WBV) and postural load and in a control group of 85 maintenance workers employed at the same transport company. The group of port machinery operators included 85 straddle carrier drivers, 88 fork-lift truck drivers, and 46 crane operators. The vector sum of the frequency-weighted r.m.s. acceleration of vibration measured on the seatpan of port vehicles and machines averaged 0·90 m/s2 for fork-lift trucks, 0·48 m/s2 for straddle carriers, 0·53 m/s2 for mobile cranes, and 0·22 m/s2 for overhead cranes. The 12-month prevalence of low back symptoms (LBP, sciatic pain, treated LBP, sick leave due to LBP) was significantly greater in the fork-lift truck drivers than in the controls and the other two groups of port machinery operators. After adjusting for potential confounders, the prevalence of low back symptoms was found to increase with the increase of WBV exposure expressed as duration of exposure (driving years), equivalent vibration magnitude (m/s2), or cumulative vibration exposure (yr m2/s4). An excess risk for lumbar disc herniation was observed in the port machinery operators with prolonged driving experience. In both the controls and the port machinery operators, low back complaints were strongly associated with perceived postural load assessed in terms of frequency and/or duration of awkward postures at work. Multivariate analysis showed that vibration exposure and postural load were independent predictors of LBP. Even though the cross-sectional design of the present study does not permit firm conclusions on the relationship between WBV exposure and low back disorders, the findings of this investigation provide additional epidemiological evidence that seated WBV exposure combined with non-neutral trunk postures, as while driving, is associated with an increased risk of long-term adverse health effects on the lower back.
Article
In a longitudinal study, the dose–response relationships between long term occupational exposure to whole-body vibration and degenerative processes in the lumbar spine caused by the lumbar disks were examined. From 1990 to 1992, 388 vibration-exposed workers from different driving jobs were examined medically and by lumbar X-ray. For each individual, a history of all exposure conditions was recorded, and a cumulative vibration dose was calculated allowing comparisons between groups of low, middle, and high intensity of exposure. 310 subjects were selected for a follow-up four years later, of whom 90·6% (n=281) agreed to participate. In comparing the exposure groups, the results indicate that the limit value ofazw(8h)=0·8 m/s2should be reviewed. The best fit between the lifelong vibration dose and the occurrence of a lumbar syndrome was obtained by applying a daily reference ofazw(8h)=0·6 ms2as a limit value. The results became more distinct still when only those subjects were included in the statistical analysis who had had no lumbar symptoms up to the end of the first year of exposure. The prevalence of lumbar syndrome is 1·55 times higher in the highly exposed group when compared to the reference group with low exposure (CI95%=1·24/1·95). Calculating the cumulative incidence of new cases of lumbar syndrome in the follow-up period yields a relative risk ofRRMH=1·37 (CI95%=0·86/2·17) for the highly exposed group. It is concluded that the limit value for the calculation of an individual lifelong vibration dose should be based on a daily reference exposure ofazw(8h)=0·6 m/s2. With increasing dose it is more and more probable that cases of lumbar syndrome are caused by exposure to vibration.
Article
During the past five years, a number of epidemiological studies on occupational exposure to whole-body vibration have been carried out at the Coronel Laboratory. These studies include both retrospective follow-up studies on long-term sick leaves and disability pensioning among crane-operators () and tractor drivers () and questionnaire studies on the prevalence of back pain among tractor drivers (), helicopter pilots () and lift-truck drivers (). Measurements (according to the ISO 2631 (1985)) were conducted to establish the accelation levels of the tractors, the helicopters and the lift-trucks. The prevalence of back pain, in most studies, was significantly higher among workers exposed to whole-body vibration compared to workers not exposed to whole-body vibration. Incidence rates of sick leave and disability pensioning due to back disorders, in particular intervertebral disc disorders, were in some studies higher in occupations that expose workers to whole-body vibration. The relationship between the received vibration dose and the prevalence of back pain as observed in these studies is explored.
Article
A cross-sectional study was conducted to investigate the risks from whole-body vibration and posture demands for low back pain (LBP) among forklift truck (forklift) drivers. Using a validated questionnaire, information about health history was obtained over a period of two weeks in face-to-face interviews. The forklift drivers were observed in respect of their sitting posture, including frequency with which different positions were adopted (bending, leaning and twisting) and postural analyses were conducted using the OWAS and RULA techniques. Forklift vibrations at the seat (exposure) were measured in the three orthogonal axes (x-fore and aft, y-lateral and z-vertical) under actual working conditions according to the recommendations of ISO 2631-1. The results showed that LBP was more prevalent amongst forklift drivers than among non-drivers and driving postures in which the trunk is considerably twisted or bent forward associated with greatest risk. Furthermore, forklift drivers showed to be exposed to acceptable levels of vibration in the x- and y-directions (i.e., below the EU Physical Agents Directive on Vibration Exposure recommended action level—0.5 m/s2), but not in the z-direction. There were indications that whole-body vibration acts associatively with other factors (not independently) to precipitate LBP.
Article
Construction is among the leading industries in work-related injuries and workers' compensation costs. Among the construction trades, operating engineers are exposed to unique job-related musculoskeletal demands. Their environmental stressors tend to be more postural and sustained in nature when compared with other construction trades. To reduce the incidence of work- related musculoskeletal disorders (WMDs) and associated compensation costs, an evaluation of the operating engineers' trade was performed. Questionnaires were mailed to 1075 members of an operating engineers' local union. 410 members responded to the symptom and job factors questionnaire. Analysis of the responses identified a lower rate of self-reported symptoms among operating engineers when compared with other construction trades. Within their trade, operating engineers reported the greatest incidence of symptoms, physician visits, and missed work related to the low back, neck, and shoulder regions. The job factors reported to contribute the most to WMDs included prolonged time in the same posture, awkward trunk postures, environmental conditions, and continuing to work when injured or hurt. The uniqueness of the operating engineer's trade relative to other construction trades provides different opportunities for intervention strategies. Operating engineers spend nearly all of their time in a work environment designed by the equipment manufacturer. This allows for working environment interventions to be made by the manufacturer and circumvents some of the less-effective methods of ergonomic intervention such as education and peer accountability. The results of the survey suggest that recent changes in equipment design have aided in a reduction in musculoskeletal complaints among operating engineers. Therefore, based on the findings of this investigation, acquisition of new equipment and continued changes in the ergonomics of equipment appear to be a primary method of intervention when attempting to reduce WMDs among operating engineers.
Article
This study investigates the effects of the main characteristics of the working condition on the vibration exposure on fork-lift trucks. Four hundred and eighty recordings were made on five trucks equipped with four different types of tyres and a ‘normal’ or an ‘anti-vibration’ seat, driven while empty or loaded, on a smooth or a rough track by three workers. An analysis of variance was performed to study the main effects and the significant interactions between these factors. A mathematical model is proposed for the weighted acceleration on the floor and on the seat in the vertical axis. This shows quantitatively that the vibration exposure is mainly influenced by the roughness of the track, the speed and the quality of the seat. Inflated tyres are preferable when an anti-vibration seat with a very low resonance frequency is used. In other cases, cushion tyres are more indicated.
Article
A case-control study of the epidemiology of acute herniated lumbar intervertebral discs in the New Haven, Connecticut, area indicates that sedentary occupations increase the risk for herniated lumbar discs, particularly among those aged 35 years and older who have had sedentary jobs for several years. People in occupations requiring prolonged driving of motor vehicles, such as truck drivers, appear to be at particularly high risk. The results of this study provide no evidence that people whose jobs involve heavy manual labour are at greater risk for acute herniated lumbar disc than others of their age and sex.
Article
To study the effects of construction machinery operation on subjective symptoms, a questionnaire survey was carried out among construction machinery operators by a self-reporting method. Subjects were 184 power shovel operators, 127 bulldozer operators, 44 forklift operators as operator groups, and 44 office workers as a control. Their ages were in a range of 30-49 years. The questionnaire contained 20 symptoms referring to fatigue, digestive problems, and upper or lower limbs or back problems. The prevalence rate and symptom characteristics were examined. The dominant symptoms of the operator groups were stiff shoulder, low back pain, and stomach symptoms. The prevalence rate of low back pain was significantly different between forklift operators and controls. No significant differences were found in the symptoms of upper limbs and fingers between operator groups and controls. The prevalence of Raynaud's phenomenon was 0.5%-2.3% in the operator groups and 2.3% in the control group.
Article
To study the long-term health effect of whole-body vibration, a questionnaire on symptoms of ill health was mailed to 242 drivers and a reference group of 210 workers from six harbor companies (response 81%). Vehicles driven were fork-lift trucks and freight-container tractors. Vibration level during a representative working period (vector sum of the frequency weighted acceleration in the x-, y-, and z-directions) was 0.8 m/sec2 for the fork-lift trucks and 1.0 m/sec2 for the freight-container tractors. Only the results concerning self-reported symptoms of the back are described. Of the young (less than 35 years), short-term-exposed drivers, 68% reported that they had back pain regularly vs. only 25% of the reference group of comparable age. With increasing age, the difference in the prevalence of self-reported regular back pain between the drivers and the reference group disappeared. Driving during the 5 years preceding the onset of symptoms seemed to increase the risk of back pain, whereas earlier exposure did not.
Article
A survey among workers in a steel factory was conducted to determine the risk for low-back pain (LBP) among male crane operators. Crane operators (n = 33) were matched for age with male control workers (n = 30) and examined for frequency and nature of LBP by the on-site medical service. Comparison between crane operators and controls showed a statistically significant odds ratio for LBP of 3.6. Although crane operators had been exposed more often to backstraining factors in previous occupations, in the employed logistic analysis only their current job explained the elevated occurrence of LBP. It is suggested that workers in sedentary position with exposure to whole-body vibration are at special risk for LBP. The results of this study provide evidence to strongly recommend persons with a history of back complaints not to seek employment as crane operators.
Article
In a population of 240 male fork-lift truck drivers who drove at least 4 h daily, the occurrence of low-back trouble was studied in relation to that of two reference groups. The participation rate of the fork-lift truck drivers was 88%. The responses to a questionnaire concerning low-back trouble were reviewed. Among the fork-lift truck drivers, a statistically significant higher occurrence of low-back trouble was reported for the year preceding the study, in comparison, according to age, to that of a reference group of 399 working men (65 against 47%); however, there was no significantly increased frequency when compared to that of a reference group of 66 unskilled male workers (65 against 51%). The fork-lift truck drivers had a significantly higher rate of absence from work within the previous year due to low-back trouble than the two reference groups (22% compared to 7 and 9%). These findings were confirmed during the follow-up year. A correlation was found between length of employment as a fork-lift truck driver and the occurrence of low-back trouble within the preceding year. It was concluded that fork-lift truck driving may be a contributory cause for low-back trouble.
Article
This paper reports on the oxygen uptake in seated volunteers subjected to 5 Hz sinusoidal vibration at 2ms, axial rotation alone and axial rotation in combination with vibration. Compared to non-vibrated, non-twisted tests, the axial rotation and vibration exposure increased the oxygen uptake by 32%.
Article
The method of cross-modality matching was used to study the development of discomfort during a 1 hour exposure to whole-body vibration. The subject's task was to adjust a broadband noise to the level where it gave rise to the same degree of discomfort as a vibration. Random vertical vibrations were used with a resonance of either 3·1 or 6·3 Hz. The sound settings were transformed into vibration levels by means of sound-vibration functions determined for each subject.The sound-level settings increased as a function of exposure time and control measurements showed that this could not have been the effect of a lowered sensitivity to the noise. The increase, expressed as log acceleration, was a linear function of log exposure time. It is therefore concluded that results from studies of shorter exposure times might be extrapolated to exposure periods of at least 1 hour. Although the method employed probably led to an underestimation of the increase in discomfort over time, the experiment does imply that the increase is overestimated by ISO standard 2631.
Article
A series of experiments were performed using ft laboratory simulation of a fork-lift truck setting task. In general, the same effects were observed as found in an another study using fork-lift trucks except that the direction of errors was reversed, showing a reversal of movement relationships in the simulator. The visual angle between the drivers' direction of motion and his line of sight to the target had a large effect on performance times and error rates. When this angle was less than 12°, both times and errors increased sharply. Performance times at different movement amplitudes and target widths were a linear function of an Index of Difficulty except for target widths of less than 2% of the amplitude. Subject age and experience of fork-lift truck driving had a significant effect of performance. Augmentation of vision using a closed circuit television display was beneficial to performance, reducing times by 14% and errors by 52% showing that this is an economic proposition for materials handling vehicles.
Article
Whole body vibration is an environmental stressor to which a substantial portion of the American workforce has been exposed. Numerous experimental studies have examined the acute effects of exposure to WBV but only in the last decade have the chronic effects been addressed. However, to date, no comprehensive review has been conducted of this common occupational exposure. This paper critically reviews the existing literature and summarizes the known health effects. Experimental study results are generally inconsistent and dependent on the characteristics of the vibration exposure. NIOSH's epidemiological studies have shown that several disorders are more prevalent in some occupations; however, causal relationships have not been established. Health professionals should be aware of potential ill effects that may result from exposure to WBV in combination with other environmental stressors.
Article
Disorders and complaints in the neck and shoulder regions are common among industrial workers and are often attributed to occupational musculoskeletal stress. The possible pathophysiological mechanism of occupational stress on the neck and shoulders is reviewed. A mechanical origin for cervical disc degeneration and osteoarthrosis is reported for a few occupational groups. However, a mechanical origin for osteoarthrosis is debatable. A work posture involving elevated arms may accelerate degeneration of shoulder tendons through impairment of circulation due to static tension and humeral compression against the coracoacromial arch. Furthermore, work tasks with repetitive arm movements may evoke shoulder tendinitis or tendo-vaginitis, probably due to friction. Three possible routes to neck-shoulder muscular pain are discussed; mechanical failure, local ischemia and energy metabolism disturbance.
Article
An increased risk of musculoskeletal disorders, e.g. from the neck region, has been found among professional drivers of work vehicles. The purpose of this study was to identify causes of postural load and implications for vehicle design and work tasks. A second purpose was to develop the methods for measurement and analysis of head postures. Field measurements of head postures for drivers of fork lift trucks, forestry machines, and cranes were carried out. The equipment used was an electric goniometer measurement system, containing a mechanical transmission between the head and the upper trunk. Methods for data presentation and quantification were developed. The results showed that rotatable and movable driver cabins improved head postures and viewing angles substantially. Narrow window frame structures and large, optimally-placed windows were also advantageous. The steering wheel, controls, and a high backrest restricted shoulder rotation, which increased head rotation in unfavourable viewing angles. Improved workspace layouts and work organization factors such as job enlargement decreased the influence of strenuous postures. The results also showed that head postures should be analysed in two or three dimensions simultaneously, otherwise the postures taken will be underestimated in relation to the maximal voluntary movement.
Article
In this study the effectiveness of the seat suspension on the transmission of whole-body vibration through the driver's seat has been determined. Eleven types of seat frequently used in lorries, agricultural tractors and fork-lift trucks were selected. The transmissibility coefficient of each seat was measured by the ratio of the acceleration (weighted root-mean-square in the vertical axis) at the interface between the seat surface and the human body to the vibration at the attachment points of the seat on the vehicle floor. Measurements in the laboratory, using standardized representative vehicle vibration spectra and two volunteers of different weights, showed transmissibility coefficients of 0.34–1.28. Attenuation of the vibration input spectrum was obtained in 20 out of 24 (83%) measurements. Measurements in the field, conducted in vehicles under representative working conditions, showed transmissibility coefficients of 0.60–1.45. Attenuation of the vibration spectrum was obtained in 17 out of 24 (71%) vehicle-seat combinations. No significant differences were observed between seats with conventional suspension and those with air suspension. Laboratory measurements of the dynamic response of the seat suspension did no provide an adequate basis for predicting its performance in the field. In most work situations the magnitude and duration of vibration exceeded the 8 h fatigue-decreased proficiency boundary of 0.32 m s⁻² in the vertical axis, which indicates that in many working situations with a daily exposure of 8 h or more suspended seats will not protect professional drivers from harmful exposure to whole-body vibration.
Article
The risk of experiencing low back pain is associated with mechanical factors. Anatomic factors, such as advancing pregnancy, can also place extra mechanical stress on the lower back. Mechanical factors, such as those related to the workplace, can be minimized by ergonomic interventions. A constrained, seated posture, in combination with exposure to whole-body, jolt/vibration can impose significant stresses on the posterior intervertebral disc and can lead to back muscle fatigue. Interventions that reduce the jolt/vibration magnitude and duration of exposure will decrease the mechanical work performed on the intervertebral disc. Such interventions range from jolt/vibration isolating seats and vehicle cabs, to decreasing exposure time and maintaining simple supported postures during ingress and egress. Improvements in seat configuration can reduce the intervertebral disc pressure and the strain on the posterior disc.
Article
Sitting in a twisted working posture is common when driving an agricultural tractor in the field. To be able to twist backwards, the driver has to overcome the torque from the passive tissues (passive resistance). The purpose of this investigation was to determine the relationship between passive resistance at axial rotation and twisting angle of the trunk when a person is seated. Ten healthy tractor drivers and 10 healthy office workers were passively twisted about the cranio-sacral axis with simultaneous measurements of the torque needed to twist them and the twisting angle. Surface electromyogram was used to control the relaxation of the muscles of the subjects. An exponential function was fitted to the data, which shows that passive resistance increases progressively with twisting angle. No significant differences in trunk passive resistance due to the subject's occupation, direction of twist or their interactions could be found. The fitted function is useful when assessing the load in the trunk in tractor driving, but also for other occupational activities where the trunk is twisted.
Article
A subjective assessment of fork-lift truck seats has been carried out to assess the range of preferred seat dimensions and the acceptability of different seat adjustments to fork-lift truck drivers. Twelve fork-lift truck seats fitted to a fixed bench were assessed by twelve fork-lift truck drivers. For each seat, each driver completed a questionnaire that covered the following areas: eleven seat dimensions, four seat adjustments and other features (arm rests, safety belts and safety wings). The drivers assessed the dimensions of a seat chosen at random, before moving to the adjacent seat in either a clockwise or anticlockwise direction. Before each assessment, they were asked to look forward and backward in the seat as though they were driving a fork-lift truck. In general, significant correlations were obtained between the subjective assessments and objective measurements of the seat dimensions. This enabled preferred seat dimension ranges to be defined. Fork-lift truck drivers ranked the forward-backward and the backrest inclination adjustments as most important. The results showed that although the drivers had previous experience in the use of suspension seats, they did not understand the purpose of the weight adjustment. All adjustments should be easy to find, accessible, easy to move and they should enable a range of adjustments. In addition, clear and simple information on the seat is needed, especially for the weight adjustment. The most recently designed seats generally had dimensions within the preferred ranges compared with the older generation seats, mainly because they had more adjustments. However, the results show that adjustments on fork-lift truck seats could be improved further. Some tentative conclusions are made for the preferred fork-lift truck seat dimensions and adjustment ranges which are based on the evidence from this restricted sample of fork-lift truck drivers. They may be useful for seat and truck designers in the preparation of a standard on fork-lift truck seat dimensions.
Article
A retrospective cohort study of tractor-driving farmers (study group) and non-tractor-driving farmers (control group) matched for age, gender, generic/ethnic group, land-holding, and work routines. To determine, using magnetic resonance imaging and clinical investigations, the effect of whole-body vibrations on the back in tractor-driving farmers. Low back pain and pathologic changes in the lower backs of tractor drivers have been reported. However, no study with a control group matched for work-related risk factors has been reported. Fifty tractor-driving farmers were compared with 50 non-tractor-driving farmers matched for age, gender, ethnic group, land-holding, and work routine. Both groups were interviewed for details of work routine, assets held, family profile, and vibration exposure to assess the influence of these parameters on signs and symptoms of backache. Magnetic resonance imaging was done to assess the effect of exposure on whole-body vibration and degenerative changes in the back. Vibration measurements also were done on tractors to observe the actual severity of the vibrations. Regular work-related backache was more common among tractor-driving farmers (40%) than among non-tractor-driving farmers (18%, P = 0.015). Anthropometric evaluation showed abdominal girth and weight to be significantly higher in tractor-driving farmers (P = 0.006 and 0.046, respectively), whereas while height and arm span were similar between the two groups. Clinical examination for evidence of disc or facet degeneration showed no difference between the two groups. Evaluation of magnetic resonance images of tractor-driving farmers and non-tractor-driving farmers by an orthopedic surgeon, radiologist, and neurosurgeon showed degenerative changes to be similar between the two groups (P > 0.050). Tractor-driving farmers report backache more often than non-tractor-driving farmers, but no significant objective differences on clinical or magnetic resonance imaging evaluation were found between the two groups.
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The paper reviews the epidemiologic evidence linking low back pain (LBP) and exposure to whole body vibration (WBV). Particular emphasis is placed on studies where the exposure is quantified. Biomechanical studies show a resonance at 4-5 Hz. At the resonance the transmissibility exceeds 1.0, and is dependent on seat attenuation, posture and seat back inclination. Increased spinal loading is evidenced by increased muscle activity, muscle fatigue, and disc pressure, and by decreased stature. Physiologic changes also occur with WBV. The risk of LBP can be reduced by vibration damping, good ergonomic design, reducing exposure, and reducing other risks such as lifting.
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A previous extensive review of the literature including that from the middle of 1992 concluded that whole-body vibrations may contribute to low back pain, but that the exposure-response relationship had not been clarified. We reviewed the literature of the past 7 years to find out: (i) whether there is evidence in the recent epidemiological literature for a causal association between whole-body vibrations and low back pain, and (ii) if there is evidence in the recent literature for a dose-response relationship between whole-body vibrations and low back pain. All relevant epidemiological articles which were obtained through a search in the databases MEDLINE, OSH-ROM and TOXLINE, and through personal communication, were reviewed independently by the two authors, using a checklist. Twenty-four original articles concerning the association between whole-body vibrations and the lower back were retained for use. The quality of the papers was mostly low, but improved with time. Only seven articles passed our predetermined quality criteria. Of the seven reports, one showed increased frequency of lumbar prolapse in occupational drivers, and six showed low back pain to be more frequent in whole-body vibration-exposed groups. Only two out of the four articles reporting on dose, showed a dose-response association. Despite the lack of definite evidence, we found sufficient reasons for the reduction of whole-body vibration-exposure to the lowest possible level. If new knowledge is to be produced, good prospective studies with repeated measurements of exposure, analyses of work postures, and clear definitions and subgroupings of low back pain are needed. Other research in this field should be given up, and the resources used for more important issues, as the size of the problem of whole body vibration is probably on the decrease because of the technical prophylactic developments that are already in progress.