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Showing papers in "Ergonomics in 1999"


Journal ArticleDOI
TL;DR: Results suggest that, in terms of performance, human operators benefit most from automation of the implementation portion of the task, but only under normal operating conditions; in contrast, removal of the operator from task implementation is detrimental to performance recovery if the automated system fails.
Abstract: Various levels of automation (LOA) designating the degree of human operator and computer control were explored within the context of a dynamic control task as a means of improving overall human/machine performance. Automated systems have traditionally been explored as binary function allocations; either the human or the machine is assigned to a given task. More recently, intermediary levels of automation have been discussed as a means of maintaining operator involvement in system performance, leading to improvements in situation awareness and reductions in out-of-the-loop performance problems. A LOA taxonomy applicable to a wide range of psychomotor and cognitive tasks is presented here. The taxonomy comprises various schemes of generic control system function allocations. The functions allocated to a human operator and/or computer included monitoring displays, generating processing options, selecting an 'optimal' option and implementing that option. The impact of the LOA taxonomy was assessed within a dynamic and complex cognitive control task by measuring its effect on human/system performance, situation awareness and workload. Thirty subjects performed simulation trials involving various levels of automation. Several automation failures occurred and out-of-the-loop performance decrements were assessed. Results suggest that, in terms of performance, human operators benefit most from automation of the implementation portion of the task, but only under normal operating conditions; in contrast, removal of the operator from task implementation is detrimental to performance recovery if the automated system fails. Joint human/system option generation significantly degraded performance in comparison to human or automated option generation alone. Lower operator workload and higher situation awareness were observed under automation of the decision making portion of the task (i.e. selection of options), although human/system performance was only slightly improved. The implications of these findings for the design of automated systems are discussed.

987 citations


Journal ArticleDOI
TL;DR: Physical exposure to risks for potential work-related musculoskeletal injuries has been assessed using a variety of methods, including pen and paper based observation methods, videotaping and computer-aided analysis, direct or instrumental techniques, and various approaches to self-report assessment.
Abstract: Physical exposure to risks for potential work-related musculoskeletal injuries has been assessed using a variety of methods, including pen and paper based observation methods, videotaping and computer-aided analysis, direct or instrumental techniques, and various approaches to self-report assessment. These methods are critically reviewed in this paper. The applications of these techniques in ergonomic and epidemiologic studies are considered, and their advantages and shortcomings are highlighted. Finally, a strategy that considers both the ergonomics experts' view and the practitioners' needs for developing a practical exposure assessment tool is then discussed.

560 citations


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

398 citations


Journal ArticleDOI
TL;DR: In this paper, the same subjects drove a laboratory driving simulator using two visual fidelity levels: a colour scene with relatively high detail, and a monochrome (night) scene showing only road-edge markings.
Abstract: Driving performance in an instrumented vehicle was compared with performance in a low-cost, fixed-based driving simulator. Six men and six women drove a freeway route while periodically dialling simulated phone calls. The same subjects drove a laboratory driving simulator using two visual fidelity levels: a colour scene with relatively high detail, and a monochrome (night) scene showing only road-edge markings. Lane position, speed, steering-wheel angle and throttle position were recorded in both contexts. Lane-keeping in the simulator was less precise than on the road, but speed control performance was comparable. The SD of lane position in normal driving was about twice as large, on average, in the simulator (0.360 versus 0.165 m). Lane keeping and speed control were less precise when dialling the phone than in normal driving, both in the simulator and on the road, but the performance decrement was greater in the simulator. The addition of the phone task increased the mean lateral speed in the car by ab...

381 citations


Journal ArticleDOI
TL;DR: Attention is drawn to the role of the need for recovery, as a sign of occupationally-induced fatigue and predictor of health complaints, in future research on occupational stress.
Abstract: Work characteristics, occupationally-induced fatigue, and health complaints were investigated on the basis of questionnaire data from 363 randomized coach drivers. The hypothesis was tested that, apart from high job demands and low job control, need for recovery is an indicator of occupationally-induced health complaints. Multiple linear regression analyses showed that need for recovery was a major predictor of psychosomatic complaints, sleep complaints, and complaints of emotional exhaustion in coach drivers. The influence of job demands and job control on health problems was moderately confirmed. The results of this study draw attention to the role of the need for recovery, as a sign of occupationally-induced fatigue and predictor of health complaints, in future research on occupational stress.

326 citations


Journal ArticleDOI
TL;DR: A case study of several industrial facilities was described, finding that the corporate and facility safety incentives appeared to have an indirect, but significant negative influence on the proper reporting of workplace injuries by workers.
Abstract: Accurate reporting of work-related conditions is necessary to monitor workplace health and safety, and to identify the interventions that are most needed. Reporting systems may be designed primarily for external agencies (OSHA or workers' compensation) or for the employer's own use. Under-reporting of workplace injuries and illnesses is common due to a variety of causes and influences. Based on previous reports, the authors were especially interested in the role of safety incentive programmes on under-reporting. Safety incentive programmes typically reward supervisors and employees for reducing workplace injury rates, and thus may unintentionally inhibit proper reporting. The authors describe a case study of several industrial facilities in order to illustrate the extent of under-reporting and the reasons for its occurrence. A questionnaire and interview survey was administered to 110 workers performing similar tasks and several managers, health, and safety personnel at each of three industrial facilities. Although less than 5% of workers had officially reported a work-related injury or illness during the past year, over 85% experienced work-related symptoms, 50% had persistent work-related problems, and 30% reported either lost time from work or work restrictions because of their ailment. Workers described several reasons for not reporting their injuries, including fear of reprisal, a belief that pain was an ordinary consequence of work activity or ageing, lack of management responsiveness after prior reports, and a desire not to lose their usual job. Interviews with management representatives revealed administrative and other barriers to reporting, stemming from their desire to attain a goal of no reported injuries, and misconceptions about requirements for recordability. The corporate and facility safety incentives appeared to have an indirect, but significant negative influence on the proper reporting of workplace injuries by workers. A variety of influences may contribute to under-reporting; because of under-reporting, worker surveys and symptom reports may provide more valuable and timely information on risks than recordable injury logs. Safety incentive programmes should be carefully designed to ensure that they provide a stimulus for safety-related changes, and to discourage under-reporting. A case-control study of similar establishments, or data before and after instituting safety incentives, would be required to more clearly establish the role of these programmes in under-reporting.

311 citations


Journal ArticleDOI
TL;DR: This study investigated the relationship among measurements of friction, the biomechanics of gait, and actual slip and fall events to develop a method for estimating the probability of slips and falls based on measurements of available friction and required friction.
Abstract: This study investigated the relationship among measurements of friction, the biomechanics of gait, and actual slip and fall events. The goal was to develop a method for estimating the probability of slips and falls based on measurements of available friction and required friction. Five subjects wearing safety harnesses walked down a ramp at various angles with either a tile or carpeted surface under dry, wet or soapy conditions. Ramp angles of 0 degree, 10 degrees and 20 degrees were used to vary the shear and normal foot force requirements. The dynamic coefficient of friction (DCOF) of shoe, floor surface and contaminant interfaces was measured. Required friction was assessed by examining the foot forces during walking trials when no slips occurred. Slips with recoveries and slips resulting in falls were recorded and categorized using a force plate and high-speed video camera. These data were then incorporated into a logistic regression to model the probability of a slip or fall event occurring based on the difference between the COF required by the foot forces generated and the measured DCOF. The results showed that the number of slip and fall events increased as the difference between the required COF and the measured DCOF increased. The logistic regression model fit the data well, resulting in an estimate of the probability of a slip or fall event based on the difference between the measured and required friction. This type of model could be used in the future to evaluate slip resistance measurement devices under various environments and assist in the design of safer work environments.

310 citations


Journal ArticleDOI
TL;DR: In this paper, the authors focus on organizations that manage complex, potentially hazardous technical operations with a surprisingly low rate of serious incidents and show that operational safety is more than the management or avoidance of risk or error.
Abstract: Empirical work on organizations that manage complex, potentially hazardous technical operations with a surprisingly low rate of serious incidents shows that operational safety is more than the management or avoidance of risk or error. Safety so defined is an ongoing intersubjective construct not readily measured in terms of safety cultures, structures, functions, or other commonly used descriptors of technical or organizational attributes that fail fully to take into account collective as well as individual agency. In the cases that the author has studied, it is represented by the interactive dynamic between operators and managers, as well as their engagement with operational and organizational conditions. The maintenance of safe operation so defined is an interactive, dynamic and communicative act, hence it is particularly vulnerable to disruption or distortion by well-meant but imperfectly informed interventions aimed at eliminating or reducing ‘human error’ that do not take into account the importance ...

309 citations


Journal ArticleDOI
TL;DR: It is argued that optimal warnings could be achieved by adjusting certain sound attributes of auditory icons, as part of a structured, user-centred design and evaluation procedure.
Abstract: In the context of emergency warnings, auditory icons, which convey information about system events by analogy with everyday events, have the potential to be understood more quickly and easily than abstract sounds. To test this proposal, an experiment was carried out to evaluate the use of auditory icons for an in-vehicle collision avoidance application. Two icons, the sounds of a car horn and of skidding tyres, were compared with two conventional warnings, a simple tone and a voice saying 'ahead'. Participants sat in an experimental vehicle with a road scene projected ahead, and they were required to brake in response to on-screen collision situations and their accompanying warning sounds. The auditory icons produced significantly faster reaction times than the conventional warnings, but suffered from more inappropriate responses, where drivers reacted with a brake press to a non-collision situation. The findings are explained relative to the perceived urgency and inherent meaning of each sound. It is argued that optimal warnings could be achieved by adjusting certain sound attributes of auditory icons, as part of a structured, user-centred design and evaluation procedure.

228 citations


Journal ArticleDOI
TL;DR: Reactions to using a conventional keyboard on a DT system were positive, and there were significant improvements in wrist posture, seated posture and upper body musculoskeletal discomfort for the test group using the DT system.
Abstract: The effects of a downward-tilting (DT) keyboard tray on wrist posture, seated posture and self-assessed musculoskeletal discomfort were investigated in a field experiment. Thirty-eight professional office workers were studied. A pretest assessed how they typed using either a conventional keyboard on a desk or on an articulating keyboard tray, and with or without wrist rests. Workers were randomly allocated to a control (n = 15) or test group (n = 23) that used their existing keyboard in a DT system. A post-test was conducted 3 weeks later. Results showed no significant changes in wrist posture, seated posture or reports of musculoskeletal discomfort for the control group, and approximately 50% of typing wrist movements put the hand in a neutral zone. There were significant improvements in wrist posture, seated posture and upper body musculoskeletal discomfort for the test group using the DT system. Over 80% of typing wrist movements put the hand into a neutral zone with the DT arrangement. Reactions to using a conventional keyboard on a DT system were positive.

200 citations


Journal ArticleDOI
TL;DR: In many participants the carpal tunnel pressures measured during mouse use were greater than pressures known to alter nerve function and structure, indicating that jobs with long periods of intensive mouse use may be at an increased risk of median mononeuropathy.
Abstract: Computer mouse use has become an integral part of office work in the past decade. Intensive mouse use has been associated with increased risk of upper extremity musculoskeletal disorders, including carpal tunnel syndrome. Sustained, elevated fluid pressure in the carpal tunnel may play a role in the pathophysiology of carpal tunnel syndrome. Carpal tunnel pressure was measured in 14 healthy individuals while they performed tasks using three different computer mice. Participants performed a multidirectional dragging ('drag and drop') task starting with the hand resting (static posture) on the mouse. With one mouse, an additional pointing ('point-and-click') task was performed. All mice were associated with similar wrist extension postures (p = 0.41) and carpal tunnel pressures (p = 0.48). Pressures were significantly greater during dragging and pointing tasks than when resting the hand (static posture) on the mouse (p = 0.003). The mean pressures during the dragging tasks were 28.8-33.1 mmHg, approximately 12 mmHg greater than the static postures. Pressures during the dragging task were higher than the pointing task (33.1 versus 28.0 mmHg), although the difference was borderline non-significant (p = 0.06). In many participants the carpal tunnel pressures measured during mouse use were greater than pressures known to alter nerve function and structure, indicating that jobs with long periods of intensive mouse use may be at an increased risk of median mononeuropathy. A recommendation is made to minimize wrist extension, minimize prolonged dragging tasks and frequently perform other tasks with the mousing hand.

Journal ArticleDOI
TL;DR: In this paper, the effect of the positioning of an attentionally demanding in-car task on the driver's ability to detect the approach of a decelerating car ahead was examined.
Abstract: This on-road study examined the effect of the positioning of an attentionally demanding in-car task on the driver's ability to detect the approach of a decelerating car ahead. Twelve participants aged between 19 and 27 years with an average of 18 170 km life-time driving experience drove 20 and 40 m behind a vehicle which decelerated from 50 km/h at 0.7 m/s2 without braking. Detection thresholds for nine locations of a LED display were compared with thresholds when focusing on the car ahead. A strong inverse relationship was found between time-to-collision (TTC) and eccentricity of the task to the normal line of sight, with TTC decreasing from 6 to 8 s at 0° eccentricity to 4 s at 90°. The results suggest that there are optimal locations, in terms of detecting the deceleration of a car ahead, for positioning attentionally demanding in-car devices, and that there are some differences in detection thresholds for similar eccentricities in the vertical and horizontal peripheries of the eye. Keywords: Driver distraction; Language: en

Journal ArticleDOI
TL;DR: It was found that children showed a modest but significant improvement in on-task behaviour and a marked change in sitting positions following the introduction of the newly-designed furniture.
Abstract: Children spend a large part of their school days in the classroom, and yet the effect of the design of school furniture on their behaviour and health has received comparatively little attention in the UK An experimental study is reported that compares the effects on children's behaviour and sitting position of traditional classroom furniture with a recently designed chair known as 'Chair 2000' and associated tables It was found that children showed a modest but significant improvement in on-task behaviour and a marked change in sitting positions following the introduction of the newly-designed furniture However, these benefits need to be considered in the light of polarized opinion for and against the new furniture, and a high level of reported incidence of back pain significantly related to the frequency of non-standard sitting In the absence of radically redesigned furniture, it is suggested that children should be given more choice in their seating, and better guidance should be given to individuals involved in education in order to inform their decision-making about classroom furniture and the postural, anthropometric and orthopaedic aspects of sitting and related activities

Journal ArticleDOI
TL;DR: The need for study designs to be founded on a better understanding of the potential damage mechanisms, and points the way towards which areas should be investigated, is highlighted.
Abstract: Musculoskeletal disorders are the most common self-reported, work-related illness in the UK, with upper limb disorders ranking second only to back complaints. The rapid increase in disablement cases, the reduced productivity resulting from the disorders, and, perhaps, the threat of litigation which is on the increase, has led to an increased awareness of the problems and an increasing desire to reduce the incidence of such disorders. This paper reviews the problem of upper limb disorders and focuses on those disorders that could be associated with repetitive manual work in industry. The disorders are described and categorized, and potential occupational risk factors are discussed and related to the injuries. In addition, a number of preventive measures, in the form of ergonomics design changes and changes in workplace practice are reviewed. There are frequent calls for well-designed epidemiological studies, so that meaningful dose-response relationships can be drawn up. A significant part of good study design is associated with measurement and analysis of the user-tool interface and the working environment. With this in mind, a variety of measurement techniques are described. Furthermore, this paper highlights the need for study designs to be founded on a better understanding of the potential damage mechanisms, and points the way towards which areas should be investigated.

Journal ArticleDOI
TL;DR: The results have visual performance implications in many tasks that are susceptible to changes in visual fields and peripheral vision, and knowledge of the dynamics of the visual field as a function of mental workload can offer significant advantages in mathematical modelling of visual search.
Abstract: Mental workload is known to reduce the area of one's visual field, but little is known about its effects on the shape of the visual field Considering this, the visual fields of 13 subjects were measured concurrently under three levels of mental workload using a Goldmann visual perimeter Tone counting tasks were employed to induce mental workload, avoiding interference with visual performance Various methods of shape measurement and analysis were used to investigate the variation of the shape of the visual field as a function of mental load As expected, the mean area of visual fields reduced to 922% in the medium workload condition and to 8641% under heavy workload, compared to light load condition This tunnelling effect was not uniform, but resulted in statistically significant shape distortion as well, as measured by the majority of the 12 shape indices used here These results have visual performance implications in many tasks that are susceptible to changes in visual fields and peripheral vision Knowledge of the dynamics of the visual field as a function of mental workload can offer significant advantages also in mathematical modelling of visual search

Journal ArticleDOI
TL;DR: Differences in the pattern of sickness responses exhibited by coach travellers suggest habituation through greater travel regularity may occur independently of reductions in travel sickness that occur with age; females are more affected by poor forward visibility than males; and the incidence of travel sickness could be significantly reduced by improving the external visibility afforded to passengers.
Abstract: The aim of this research was to identify personal and environmental factors influencing individual susceptibility to motion sickness during road transport. A questionnaire survey of 3256 coach travellers was conducted. Information on passenger characteristics, travel regularity, activity during travel, use of anti-motion sickness drugs and self-reported motion sickness susceptibility were collected over 56 private hire coach journeys. Details of the travel environment (visibility, temperature and seating) were also recorded. The relationship of these variables with passenger illness and more specific symptoms of motion sickness are examined. Overall, 28.4% of passengers reported feeling ill, 12.8% reported nausea and 1.7% reported vomiting during coach travel. Travel sickness decreased with increasing passenger age and greater travel experience. Females were more likely to report feeling ill during coach travel than males by a ratio of four to three. Poor forward visibility was found to increase sickness. Passenger illness occurrence was approximately three times higher for passengers with no view of the road ahead (mean, 34.6%) compared to passengers who could see the road ahead extremely well (mean, 12.7%). No relationships were found between the occurrence of travel sickness and temperature or time of travel. Differences in the pattern of sickness responses exhibited by coach travellers suggest: (1) habituation through greater travel regularity may occur independently of reductions in travel sickness that occur with age; (2) females are more affected by poor forward visibility than males; and (3) the incidence of travel sickness could be significantly reduced by improving the external visibility afforded to passengers.

Journal ArticleDOI
TL;DR: This study considered the hypothesis that on some tasks men and women might employ different information processing strategies and demonstrated a near-significant overall reaction time advantage for male participants, while males and females showed a differential pattern of reaction time as a function of stimulus location.
Abstract: This study considered the hypothesis that on some tasks men and women might employ different information processing strategies. Twelve male and 12 female participants performed a 2- and 4-choice, compatible and incompatible, choice reaction time task that required a verbal response to a spatial location target stimulus. Results demonstrated a near-significant overall reaction time advantage for male participants. Moreover, males and females showed a differential pattern of reaction time as a function of stimulus location. Specifically, in the 4-choice-compatible condition, females exhibited a linear increase in reaction time as a function of the left-right dimension; males, on the other hand, showed a two-component, step-like increase. It was suggested that this gender difference in reaction time performance may reflect differences in processing strategy. Specifically, it was argued that in the present task females may have employed a serial, left-to-right, processing strategy, and males a binary, split-half (dichotomizing) strategy.

Journal ArticleDOI
TL;DR: Passenger nausea and illness ratings increased with increased exposure to lateral coach motion at low frequencies, and motion in other axes correlated less well with sickness, although there were some intercorrelations between the motions in the different axes.
Abstract: Relationships between vehicle motion and passenger sickness have been investigated in a survey of 3256 passengers travelling on 56 mainland UK bus or coach journeys. Vehicle motion was measured throughout all journeys, yielding over 110 h of six-axis coach motion data from five types of coach and 17 different drivers. Overall, 28.4% of passengers reported feelings of illness, 12.8% reported nausea and 1.7% reported vomiting during coach travel. Passenger nausea and illness ratings increased with increased exposure to lateral coach motion at low frequencies (< 0.5 Hz). Motion in other axes correlated less well with sickness, although there were some intercorrelations between the motions in the different axes. Sickness levels among passengers were greater with drivers who drove to produce higher average magnitudes of fore-and-aft and lateral vehicle motion. Nausea occurrence was greater on routes classified as being predominantly cross-country where magnitudes of lateral vehicle motion were significantly higher. Lateral motion and motion sickness increased from the front to the rear of each vehicle. No significant differences in sickness were found between the five different vehicle types used in the study. The applicability of a motion sickness dose model to these data is discussed.

Journal ArticleDOI
TL;DR: The results indicate that the total amount of work performed by means of job rotation resulted in an overall reduced physical workload of the employees of the refuse collecting department.
Abstract: The effect of job rotation on the physical workload was investigated for male employees working at a refuse collecting department. Before the introduction of job rotation, an employee worked as a street sweeper, as a refuse collector or as a driver. After the introduction of job rotation, every employee was allowed to alternate between two of the three possible jobs during the day, i.e. refuse collecting/street sweeping, refuse collecting/driving or street sweeping/driving. Two non-rotation groups (i.e. refuse collectors and street sweepers) and two rotation groups (i.e. refuse collectors/street sweepers and street sweepers/drivers) were mutually compared. The physical workload was determined by measuring the perceived load, energetic load and postural load during a full working day. Job rotation resulted in a significant decrease of the perceived load and energetic load and a slight decrease of the postural load. The results indicate that the total amount of work performed by means of job rotation resulted in an overall reduced physical workload of the employees of the refuse collecting department.

Journal ArticleDOI
TL;DR: The importance of physical fitness as related to performance of fire suppression job tasks is shown, with the best multiple predictor of PPA being the 1.5 mile run.
Abstract: This investigation evaluated the relationship between physical fitness and performance of fire suppression tasks. The following mean±SD values were associated with 91 fire fighters: age 31.69±7.39 ...

Journal ArticleDOI
TL;DR: Evaluated commonly used types of LBD assessment methods indicated that the different measures have various strengths and weaknesses and that the measure that most appropriately assesses risk depends upon the characteristics of the job.
Abstract: Low-back disorders (LBD) continue to be the most costly and common musculoskeletal problem facing society today. Investigators have developed tools or measures that are intended to identify jobs that will probably be associated with an elevated risk of low-back disorders. However, an important and not widely discussed issue associated with these tools and procedures has been that of the validity or effectiveness of the tools. Therefore the objective of this study was to evaluate the validity and effectiveness of two commonly used types of LBD assessment methods in terms of their ability to correctly associate jobs with LBD risk. The 1981 NIOSH Work Practices Guide for Manual Lifting and the 1991 NIOSH revised lifting equation, along with psychophysical measures were assessed for their ability to correctly identify high-, medium-, and low-risk (of LBD) jobs. Risk was defined according to a database of 353 industrial jobs representing over 21 million person-hours of exposure. The results indicated that both NIOSH measures were predictive and resulted in odds ratios between 3.1 and 4.6. Higher odds ratios were found when the maximum horizontal distance was used to assess a job compared to the average horizontal distance. Further analyses indicated that the two NIOSH assessment methods classified risk in very different ways. The 1981 NIOSH Guide demonstrated good specificity (91%) in that it identified low-risk jobs well but it also displayed low sensitivity by only correctly identifying 10% of the high-risk jobs. The 1993 NIOSH revised lifting equation, on the other hand, had better sensitivity. It correctly identified 73% of the high-risk jobs but did not identify low- and medium-risk jobs well. Using psychophysical criteria it was observed that 60% of the high-risk jobs would be judged to be acceptable, whereas, 64% and 91% of the medium- and low-risk jobs, respectively, would be judged to be acceptable. This study indicates that the different measures have various strengths and weaknesses. When controlling for occupational LBD it should be recognized that a variety of measures exist and that the measure that most appropriately assesses risk depends upon the characteristics of the job.

Journal ArticleDOI
TL;DR: The features that were found to be significantly better, after multivariate analysis, with the ergonomically designed furniture were the writing position and the chair height, independently of the other subjective perception of the school furniture.
Abstract: Apart from studies by Aagaard-Hansen and Storr-Paulsen and by Linton and others, most of the studies published on ergonomically designed furniture have been carried out with adults, usually within the office environment. The aim of this study was to evaluate two different kinds of furniture, Mandal's furniture and the ISO standard furniture for schoolchildren, in a real-life environment and on a long-term basis. This study was carried out with 263 children aged from 8 to 11 years after 4 or 5 years of using the same school furniture. Two groups were selected according to the kind of furniture. Pupils answered a questionnaire focusing on back pain and subjective perception of the school furniture. No significant differences were found concerning the prevalence of back pain among the two groups. The features that were found to be significantly better, after multivariate analysis, with the ergonomically designed furniture were the writing position and the chair height, independently of the other subjective f...

Journal ArticleDOI
TL;DR: 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.
Abstract: 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.

Journal ArticleDOI
TL;DR: Wrist motions are rapid and are similar in magnitude to wrist motions of industrial workers performing jobs having a high risk for developing cumulative trauma disorders, which suggests that wrist joint motions may need to be evaluated as a risk factor for musculoskeletal disorders during typing.
Abstract: Awkward upper extremity postures and repetitive wrist motions have been identified by some studies as risk factors for upper extremity musculoskeletal disorders during keyboard work. However, accurate body postures and joint motions of typists typing on standardized workstations are not known. A laboratory study was conducted to continuously measure wrist and forearm postures and motions of 25 subjects while they typed for 10-15 min at a standard computer workstation adjusted to the subjects' anthropometry. Electrogoniometers continuously recorded wrist and forearm angles. Joint angular velocities and accelerations were calculated from the postural data. The results indicate that wrist and forearm postures during typing were sustained at non-neutral angles; mean wrist extension angle was 23.4 +/- 10.9 degrees on the left and 19.9 +/- 8.6 degrees on the right. Mean ulnar deviation was 14.7 +/- 10.1 degrees on the left and 18.6 +/- 5.8 degrees on the right. More than 73% of subjects typed with the left or right wrist in greater than 15 degrees extension and more than 20% typed with the left or right wrist in greater than 20 degrees ulnar deviation. Joint angles and motions while typing on an adjusted computer workstation were not predictable based on anthropometry or typing speed and varied widely between subjects. Wrist motions are rapid and are similar in magnitude to wrist motions of industrial workers performing jobs having a high risk for developing cumulative trauma disorders. The magnitude of the dynamic components suggests that wrist joint motions may need to be evaluated as a risk factor for musculoskeletal disorders during typing.

Journal ArticleDOI
TL;DR: Box weight did not appear to be a feasible means of controlling spine loading unless its position on the pallet could also be controlled and the inclusion of handles had an effect similar to reducing the box weight by 4.5 kg, whereas box size did not effectively affect spine loading.
Abstract: Low back disorders in distribution centres or warehouses have been identified as an area of elevated risk in many industries. The task of an order selector requires workers manually to lift boxes from storage bins to a mobile pallet. This study explored the effect of box features and box location when lifting from a pallet in a storage bin upon spine loading. Ten experienced warehouse workers were asked to lift boxes from a pallet while the size, weight, handle features and location of the box on a pallet were changed. An EMG-assisted model was employed to assess spine compression, lateral shear and anterior-posterior shear during the lifts. The position from which the worker lifted a box on a pallet had the most profound effect on spine loading while the lower level of the pallet represented the greatest loadings on the spine. Box weight did not appear to be a feasible means of controlling spine loading unless its position on the pallet could also be controlled. The inclusion of handles had an effect similar to reducing the box weight by 4.5 kg, whereas box size did not effectively affect spine loading. The mechanisms by which these factors affect spine loading are discussed.

Journal ArticleDOI
TL;DR: The results suggest that individuals with CTS lose some ability to coordinate efficiently grip force on hand tools and exert higher grip forces on tools, at equivalent application forces, than controls, believed to be a result of tactile sensibility deficits associated with C TS.
Abstract: This study investigated coordination of the grip force on and force applied with a hand tool using a precision pinch grip. A simulated hand tool was developed to measure grip force exerted on the tool as a function of the force transmitted from the tool to an external object in a dynamic force matching paradigm. Grip force coordination measures reflected subjects' abilities to modulate grip force in parallel with the tool application force and their abilities to minimize excessive grip force. These measures were calculated for seven subjects with a diagnosis of carpal tunnel syndrome (CTS) and seven age- and gender-matched controls. The absolute magnitude of excessive grip force (safety margin) was unreliable because of the high intrasubject variability in coefficient of friction measurements. Linear regression equations predicting coefficient of friction from pinch force magnitude had low r2 coefficients of determination and were generally not statistically significant (p > 0.05). Relative comparisons of grip force control showed that individuals with CTS exhibited a statistically significant (p < 0.05) increase in ratio of grip force to application force (54% higher than controls) and a significant (p < 0.05) decrease in modulation of pinch force with application force (12% lower than controls). These results suggest that individuals with CTS lose some ability to coordinate efficiently grip force on hand tools and exert higher grip forces on tools, at equivalent application forces, than controls. This is believed to be a result of tactile sensibility deficits associated with CTS. As a result, workers with CTS may be at increased risk of accelerating the progression of their musculoskeletal disorder.

Journal ArticleDOI
TL;DR: In this article, the effect of music on driving-related tracking and vigilance tasks was examined and the results indicated that while the relatively simple tracking task was not affected by the music, response time to centrally located visual signals was improved under both music conditions and under both low and high-demand situations.
Abstract: The effect of music on driving-related tracking and vigilance tasks was examined. Participants carried out the tasks either singularly (low demand) or together (high demand) under conditions of silence, low-intensity music of high intensity music. The results indicated that while the relatively simple tracking task was not affected by the music, response time to centrally located visual signals was improved under both music conditions and under both low- and high-demand situations. High-intensity music was associated with an increase in response time to peripheral signals under high-demand conditions. The results are discussed in relation to increased selectivity of attention with music-induced arousal.

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TL;DR: Muscle activity analyzed in different phases of the movement showed that SCI people adopt different postural adjustments to face the balance changes due to the reaching movement.
Abstract: To compensate for postural muscle function loss spinal cord injured (SCI) people have to use parts of the sensorimotor system which are still intact. In this study, postural control was investigated in high and low thoracic SCI people and in able-bodied controls, using a bimanual forward-reaching task. Muscle activity was recorded bilaterally from the erector spinae (ES) at level L3, T9 and T3, latissimus dorsi (LD), ascending part of the trapezius muscle (TPA), serratus anterior (SA), sternocostal head of the pectoralis major (PM) and the oblique abdominal muscles (OA) by means of surface electromyography. Sitting balance was monitored by measuring the changes in the location of the centre of pressure (CP) using a force platform. Muscle activity analyzed in different phases of the movement showed that SCI people adopt different postural adjustments to face the balance changes due to the reaching movement. SCI people make alternative use of non-postural muscles like the LD and TPA to maintain their sitting balance.

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TL;DR: 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.
Abstract: 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.

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TL;DR: While SWR is potentially an efficient method of maintaining cardiovascular fitness, it needs to be investigated further to establish if it is a viable technique for the injured athlete to employ.
Abstract: The maximal physiological responses to treadmill running (TMR), shallow water running (SWR) and deep water running (DWR) while wearing a buoyancy vest were compared in 15 trained male runners. Measurements included oxygen consumption (VO2 max), respiratory exchange ratio (RER) and heart rate (HR). Treadmill running elicited VO2 max and HRmax, which were higher than the peaks attained in both water tests (p < 0.01). VO2 peak averaged 83.7 and 75.3% of VO2 max for SWR and DWR respectively. Peak HR for SWR and DWR were 94.1 and 87.2% of the HRmax reached in the TMR. RER responses were similar between the three modalities. The observations suggest that the training stimulus provided by water is still adequate for supplementary training. While SWR is potentially an efficient method of maintaining cardiovascular fitness, it needs to be investigated further to establish if it is a viable technique for the injured athlete to employ.