Measurement of trunk bending during work by direct observation and continuous measurement

Cost and statistical efficiency of posture assessment by inclinometry and observation, exemplified by paper mill work

Postures at work are paramount in ergonomics. They can be determined using observation and inclinometry in a variety of measurement scenarios that may differ both in costs associated with collecting and processing data, and in efficiency, i.e. the precision of the eventual outcome. The trade-off between cost and efficiency has rarely been addressed in research despite the obvious interest of obtaining precise data at low costs. Median trunk and upper arm inclination were determined for full shifts in 28 paper mill workers using both observation and inclinometry. Costs were estimated using comprehensive cost equations; and efficiency, i.e. the inverted standard deviation of the group mean, was assessed on basis of exposure variance components. Cost and efficiency were estimated in simulations of six sampling scenarios: two for inclinometry (sampling from one or three shifts) and four for observation (one or three observers rating one or three shifts). Each of the six scenarios was evaluated for 1 through 50 workers. Cost-efficiency relationships between the scenarios were intricate. As an example, inclinometry was always more cost-efficient than observation for trunk inclination, except for observation strategies involving only few workers; while for arm inclination, observation by three observers of one shift per worker outperformed inclinometry on three shifts up to a budget of €20000, after which inclinometry prevailed. At a budget of €10000, the best sampling scenario for arm inclination was 2.5 times more efficient than the worst. Arm inclination could be determined with better cost-efficiency than trunk inclination. Our study illustrates that the cost-efficiency of different posture measurement strategies can be assessed and compared using easily accessible diagrams. While the numeric examples in our study are specific to the investigated occupation, exposure variables, and sampling logistics, we believe that inclinometry will, in general, outperform observation. In any specific case, we recommend a thorough analysis, using the comparison procedure proposed in the present study, of feasible strategies for obtaining data, in order to arrive at an informed decision support.

Accuracy of a markerless motion capture system for postural ergonomic risk assessment in occupational practice

Established methods for postural ergonomic risk assessment in occupational practice are mostly time-consuming and need to be conducted by experts. Use of technology could improve postural ergonomic risk assessments with regard to time efficiency and accuracy. A study was conducted to assess the accuracy of a markerless motion capture system (Microsoft Kinect V2) compared to a marker-based motion capture system (Vicon Bonita). Angles of different body segments were analysed. The results show major inaccuracies of the markerless motion capture system for capturing axial trunk rotation (mean angular deviation of 14.04°) indicating that potential health risks could be underestimated. Combined working postures of axial trunk rotation and arm anteversion show issues with self-occlusion. Based on the findings, it is discussed whether the detected inaccuracies for axial trunk rotation are likely to lead to overestimation or underestimation of potential health risks when conducting an ergonomic risk assessment.

Trunk and upper arm postures in paper mill work

The aim of this study was to assess postures and movements of the trunk and upper arm during paper mill work, and to determine the extent to which they differ depending on method of assessment. For each of 28 paper mill workers, postures and movements were assessed during three full shifts using inclinometer registration and observation from video. Summary metrics for each shift, e.g., 10^th, 50^th, and 90^th posture percentile, were averaged across shifts and across workers. In addition, the standard deviation between workers, and the standard deviation between shifts within worker were computed. The results showed that trunk and arm postures during paper mill work were similar to other occupations involving manual materials handling, but the velocities of arm movements were lower. While postures determined by inclinometry and observation were similar on a group level, substantial differences were found between results obtained by the two methods for individual workers, particularly for extreme postures. Thus, measurements by either method on individuals or small groups should be interpreted with caution.

Investigation of observational methods assessing workload of static working postures based on surface electromyography

BACKGROUND:

A large number of different methods are available to identify and assess working postures. Although observation-based methods are most commonly used in practise, investigations showed different results regarding validity of such methods.

OBJECTIVE:

To investigate validity of one of the most commonly used observation-based assessment method in ergonomics, the Ovako Working Posture Analysing System (OWAS) and the European standard EN 1005-4 for evaluation of working postures, an experimental laboratory study was conducted.

METHODS:

Muscle activity was measured under combinations of static working postures of trunk inclination and shoulder flexion to compare these measurements and observation-based assessments according to OWAS and EN 1005-4. In order to investigate the magnitude of correspondence between muscle activity and observation-based assessments, Spearman rank correlation coefficients (r_s) were calculated.

RESULTS:

Significant correlations were found between OWAS and muscle activity (range from r_s² = 0.17 r_s² = 0.55). Significant correlations were found between EN 1005-4 and muscle activity (range from r_s² = 0.34 to r_s² = 0.74).

CONCLUSIONS:

Results emphasise a need for further developments of observation-based methods, since the two investigated methods showed a variance of validity ranging from small to large. Such improvements may also form a better basis for the ergonomic improvement of working conditions in practise, which is highly necessary due to a constantly high prevalence of MSDs in the last decades.

Validation of an ergonomic assessment method using Kinect data in real workplace conditions

Evaluating potential musculoskeletal disorders risks in real workstations is challenging as the environment is cluttered, which makes it difficult to accurately assess workers' postures. Being marker-free and calibration-free, Microsoft Kinect is a promising device although it may be sensitive to occlusions. We propose and evaluate a RULA ergonomic assessment in real work conditions using recently published occlusion-resistant Kinect skeleton data correction. First, we compared postures estimated with this method to ground-truth data, in standardized laboratory conditions. Second, we compared RULA scores to those provided by two professional experts, in a non-laboratory cluttered workplace condition. The results show that the corrected Kinect data can provide more accurate RULA grand scores, even under sub-optimal conditions induced by the workplace environment. This study opens new perspectives in musculoskeletal risk assessment as it provides the ergonomists with 30 Hz continuous information that could be analyzed offline and in a real-time framework.

Comparison of three methods for evaluation of work postures in a truck assembly plant

This study compared the results of three risk assessment tools (self-reported questionnaire, observational tool, direct measurement method) for the upper limbs and back in a truck assembly plant at two cycle times (11 and 8 min). The weighted Kappa factor showed fair agreement between the observational and direct measurement method for the arm (0.39) and back (0.47). The weighted Kappa factor for these methods was poor for the neck (0) and wrist (0) but the observed proportional agreement (P_o) was 0.78 for the neck and 0.83 for the wrist. The weighted Kappa factor between questionnaire and direct measurement showed poor or slight agreement (0) for different body segments in both cycle times. The results revealed moderate agreement between the observational tool and the direct measurement method, and poor agreement between the self-reported questionnaire and direct measurement. Practitioner Summary: This study provides risk exposure measurement by different common ergonomic methods in the field. The results help to develop valid measurements and improve exposure evaluation. Hence, the ergonomist/practitioners should apply the methods with caution, or at least knowing what the issues/errors are.

Musculoskeletal disorders: OWAS review

The prevention of musculoskeletal disorders (MSD) is very important in the world. Governments and companies are the most interested. The objective of the present work is to review the literature on the applications of the OWAS method in the diverse sectors or fields of knowledge and countries from its publication to March 2017. The use of OWAS method has been classified by categories of knowledge, by country and by year. The search was made by selecting only the main collection of the Web of Science. This was selected by the option "Advanced search" using the term OWAS (ts=OWAS) for the time period of 1900 to 2017. A total of 166 results were found, consisting of conference papers and articles in scientific journals. In conclusion, the OWAS has been applied mainly in two sectors: "Manufacturing industries" and "Healthcare and Social assistance activities". This method needs to be complemented with other indirect or direct methods. Also, whenever the OWAS has been used, whether individually or together with other methods, musculoskeletal disorders risks have been detected, this perhaps being an indicator to review the evaluation parameters because overestimating the risk.

The Effects of Distance on Psychophysically Determined Pushing and Pulling Tasks

The most frequent and expensive cause category of compensable loss is manual material handling (MMH). in an attempt to minimize these losses, refinement of existing MMH guidelines is a component of redesigning high risk MMH jobs. in the development of our present MMH guidelines (Snook & Ciriello, 1991), maximum acceptable forces (MAFs) of pulling were assumed to respond similarly to pushing at longer distances. The purpose of this experiment was to investigate the effects of 7.6m and 15.2m distances on both initial and sustained MAFs of pushing and pulling at a frequency of 1 min−1. A psychophysical methodology was used whereby the subjects were asked to select a workload without “straining themselves or without becoming unusually tired, weakened, overheated or out of breath.” Subjects worked 40 min at each push or pull task within a 4-hour test that included other MMH tasks. The results revealed that initial and sustained MAFs and task time were not significantly different between pushing and pulling at the 7.6m distance. However, at the 15.2m distance, initial MAF of pulling was significantly lower and task time was significantly longer compared to pushing. Sustained MAF was not significantly different at 15.2m. It was concluded that our existing guidelines present an accurate estimate of MAFs at the longer pull distances.

The Effects of Distance on Psychophysically Determined Pushing and Pulling Tasks for Female Industrial Workers

The most frequent and expensive cause category of compensable loss is manual material handling (MMH). In an attempt to minimize these losses, refinement of existing MMH guidelines is a component of redesigning high risk MMH jobs. In the development of our present MMH guidelines (Snook & Ciriello, 1991), maximum acceptable forces (MAFs) of pulling were assumed to respond similarly to pushing at longer distances for male and female industrial workers. The purpose of this experiment was to investigate the effects of 7.6m and 15.2m distances on both initial and sustained MAFs of pushing and pulling at a frequency of 1 min-1. A psychophysical methodology was used whereby the subjects were asked to select a workload without “straining themselves or without becoming unusually tired, weakened, overheated or out of breath.” Ten subjects worked 40 min at each push or pull task within a 4-hour test that included other MMH tasks. The results revealed that initial and sustained MAFs were not significantly different between pushing and pulling at both the 7.6m and 15.2m distance. However, task time was significantly longer for pulling at both distances. It was concluded that our existing guidelines present an accurate estimate of MAFs at the longer pull distances for female industrial workers

Pose estimation with a Kinect for ergonomic studies: evaluation of the accuracy using a virtual mannequin

Analyzing human poses with a Kinect is a promising method to evaluate potentials risks of musculoskeletal disorders at workstations. In ecological situations, complex 3D poses and constraints imposed by the environment make it difficult to obtain reliable kinematic information. Thus, being able to predict the potential accuracy of the measurement for such complex 3D poses and sensor placements is challenging in classical experimental setups. To tackle this problem, we propose a new evaluation method based on a virtual mannequin. In this study, we apply this method to the evaluation of joint positions (shoulder, elbow, and wrist), joint angles (shoulder and elbow), and the corresponding RULA (a popular ergonomics assessment grid) upper-limb score for a large set of poses and sensor placements. Thanks to this evaluation method, more than 500,000 configurations have been automatically tested, which would be almost impossible to evaluate with classical protocols. The results show that the kinematic information obtained by the Kinect software is generally accurate enough to fill in ergonomic assessment grids. However inaccuracy strongly increases for some specific poses and sensor positions. Using this evaluation method enabled us to report configurations that could lead to these high inaccuracies. As a supplementary material, we provide a software tool to help designers to evaluate the expected accuracy of this sensor for a set of upper-limb configurations. Results obtained with the virtual mannequin are in accordance with those obtained from a real subject for a limited set of poses and sensor placements.

Using Kinect™ sensor in observational methods for assessing postures at work

This paper examines the potential use of Kinect™ range sensor in observational methods for assessing postural loads. Range sensors can detect the position of the joints at high sampling rates without attaching sensors or markers directly to the subject under study. First, a computerized OWAS ergonomic assessment system was implemented to permit the data acquisition from Kinect™ and data processing in order to identify the risk level of each recorded postures. Output data were compared with the results provided by human observers, and were used to determine the influence of the sensor view angle relative to the worker. The tests show high inter-method agreement in the classification of risk categories (Proportion agreement index = 0.89 κ = 0.83) when the tracked subject is facing the sensor. The camera's point of view relative to the position of the tracked subject significantly affects the correct classification of the postures. Although the results are promising, some aspects involved in the use of low-cost range sensors should be further studied for their use in real environments.

MEASURING LUMBAR SAGITTAL POSTURE IN SEWAGE WORKERS USING AN ULTRASONIC DEVICE

Because the degree and duration of lumbar flexion during sewage work have only been assessed on the basis of subjective reports, the purpose of this study was to investigate the usability of a measurement system for the non-invasive assessment of lumbar sagittal posture during sewage work using ultrasound. The validity of an ultrasonic measurement device was investigated in 16 healthy individuals by comparing the measurements obtained with the device with both Schober and electronic inclinometer measurements. To determine the intra-rater reliability of the ultrasonic device, short-term, medium-term, and long-term test-retest data were collected. Moreover, the percentage of the work time sewage workers spend in each of seven lumbar flexion categories within their individual lumbar flexion range of motion was assessed. Pearson's correlation coefficients of ≥ 0.88 indicate high validity between the methods. The intraclass correlation coefficients between tests and retests (≥ 0.88) demonstrate high reproducibility of the measurement procedures. Sewage workers spend about 25% of their work day in the most extreme of the seven lumbar posture categories. Also, testing did not interfere with the workers' normal work routine. The validity and reliability data as well as the trouble-free technical performance of the ultrasonic device support its usability for the continuous measurement of lumbar posture during sewage work.

Physical ergonomic hazards in highway tunnel construction: overview from the Construction Occupational Health Program

This report provides an overview of physical ergonomic exposures in highway construction work across trades and major operations. For each operation, the observational method "PATH" (Posture, Activity, Tools and Handling) was used to estimate the percentage of time that workers spent in specific tasks and with exposure to awkward postures and load handling. The observations were carried out on 73 different days, typically for about 4 h per day, covering 120 construction workers in 5 different trades: laborers, carpenters, ironworkers, plasterers, and tilers. Non-neutral trunk postures (forward or sideways flexion or twisting) were frequently observed, representing over 40% of observations for all trades except laborers (28%). Kneeling and squatting were common in all operations, especially tiling and underground utility relocation work. Handling loads was frequent, especially for plasterers and tilers, with a range of load weights but most often under 15 pounds. The results of this study provide quantitative evidence that workers in highway tunnel construction operations are exposed to ergonomic factors known to present significant health hazards. Numerous opportunities exist for the development and implementation of ergonomic interventions to protect the health and safety of construction workers.

Dairy farm worker exposure to awkward knee posture during milking and feeding tasks

Musculoskeletal disorders are common among agricultural workers, particularly among dairy farm workers. Specifically, dairy farm workers have been identified as being at risk for knee osteoarthritis. Physical risk factors that may contribute to knee osteoarthritis include awkward postures of the knee, such as kneeling or squatting. The purpose of this study was to quantify exposure to awkward knee posture among dairy farm workers during milking and feeding tasks in two common types of milking facilities (stanchion and parlor). Twenty-three dairy farm workers performed milking and feeding tasks; 11 worked in a stanchion milking facility, and 12 worked in a parlor milking facility. An electrogoniometer was used to measure knee flexion during 30 min of the milking and feeding tasks. Milking in a stanchion facility results in a greater duration of exposure to awkward posture of the knee compared with milking in a parlor facility. Specifically, the percentage of time in >or=110 degrees knee flexion was significantly greater in the stanchion facility (X = 17.7; SE 4.2) than in the parlor facility (X = 0.05; SE 0.04; p <or= 0.05). Similar results were observed with other categories of awkward knee posture in both milking and feeding tasks. This study supports previous findings that working in stanchion milking facility results in greater exposure to awkward knee posture compared with working in a parlor milking facility.

Assessing combined exposures of whole-body vibration and awkward posture--further results from application of a simultaneous field measurement methodology

The drivers of ten vehicles (tram, helicopter, saloon car, van, forklift, two mobile excavators, wheel loader, tractor, elevating platform truck) were studied with regard to the combined exposures of whole-body vibration and awkward posture during occupational tasks. Seven degrees of freedom (DOFs), or body angles, were recorded as a function of time by means of the CUELA measuring system (Computer-assisted registration and long-term analysis of musculoskeletal workloads) for the purpose of posture assessment. The vibrational exposure is expressed as the vector sum of the frequency-weighted accelerations in the three Cartesian coordinates; these were recorded simultaneously with the posture measurement. Based upon the percentage of working time spent under different workloads, a scheme is proposed for classification of the two exposures into three categories. In addition, a risk of adverse health effects classified as low, possible or high can be assigned to the combination of the two exposures. With regard to posture, the most severe exposure was measured for the drivers of the wheel loader and for the tractor driver, whereas the lowest exposure was measured for the helicopter pilots and van drivers. With regard to the combination of whole-body and posture exposures, the tractor driver and the elevating platform truck driver exhibited the highest workloads.

Inter-rater reliability of PATH observations for assessment of ergonomic risk factors in hospital work

This study examined the inter-rater reliability of expert observations of ergonomic risk factors by four analysts. Ten jobs were observed at a hospital using a newly expanded version of the PATH method (Buchholz et al. 1996), to which selected upper extremity exposures had been added. Two of the four raters simultaneously observed each worker onsite for a total of 443 observation pairs containing 18 categorical exposure items each. For most exposure items, kappa coefficients were 0.4 or higher. For some items, agreement was higher both for the jobs with less rapid hand activity and for the analysts with a higher level of ergonomic job analysis experience. These upper extremity exposures could be characterised reliably with real-time observation, given adequate experience and training of the observers. The revised version of PATH is applicable to the analysis of jobs where upper extremity musculoskeletal strain is of concern.

Secular changes in psychophysically determined maximum acceptable weights and forces over 20 years for male industrial workers

The most frequent and expensive cause of compensable workplace injuries loss is manual material handling (MMH). In an attempt to minimise these losses, refinement of existing MMH guidelines is a component of redesigning high risk MMH jobs. In the development of the present MMH 1991 guidelines (Snook and Ciriello 1991), maximum acceptable weights (MAWs) and forces (MAFs) were derived from studies conducted in a 21 year time span before the above publication date. The question arises whether the present generation of workers have the same psychophysically determined weights and forces as those reflected in the guidelines. Therefore, the present study investigated whether secular changes had occurred in key MMH tasks in trials performed by present day local industrial workers. A total of 23 male industrial workers performed 20 variations of lifting, lowering, pushing, pulling and carrying tasks. A psychophysical methodology, identical to that of the authors' previous experiments, was used whereby the subjects were asked to select a workload they could sustain for 8 h 'without straining themselves or without becoming unusually tired, weakened, overheated or out of breath'. The results revealed that MAWs of lifting, lowering and carrying averaged 69% of the guideline values. MAFs of pushing and pulling showed less of a drop, averaging 82% and 94% respectively for initial and sustained forces. The results also indicated that the effects of the variables frequency, height, lifting vs. lowering, pushing vs. pulling were similar to earlier reported results, even though the absolute weights or forces were lower. It was concluded that consideration to change existing guidelines, reflecting this new psychophysical set point, may be appropriate if these significant performance decreases are confirmed in other locations, with greater subject numbers, and by other investigators.

Reliability and validity assessment of the hand activity level threshold limit value and strain index using expert ratings of mono-task jobs

This study evaluated two subjective assessment methods for physical work-related musculoskeletal disorder (WMSD) risk factors. A total of 567 participants from 12 companies in the manufacturing and health care industries were evaluated using the hand activity level (HAL) threshold limit value (TLV) and the Strain Index. Inter-rater reliability comparisons were performed on 125 selected cyclic tasks, with one novice and three experienced raters. Predictive validity was assessed by evaluation of relationships between measured exposure parameters and diagnosed WMSDs of the hand/wrist and elbow. HAL hand repetition ratings had a Spearman r value of 0.65 and a kappa value of 0.44 between raters. Subjective force (0-10 scale) estimates had a Spearman r = 0.28 and were not significantly different between raters (p > .05). The rating comparison for the four subjective components of the Strain Index had Spearman r correlations of 0.37-0.62 and kappa values of 0.25-0.44. The Strain Index and HAL TLV agreed on exposure categorization 56% of the time. Logistic regression showed, after adjustment for age, gender, and body mass index, that higher peak hand force estimates (odds ratio [OR] 1.14, confidence interval (CI) 1.02-1.27), most common force estimates (OR 1.14, CI 1.02-1.28), hand/wrist posture rating (OR 1.71, CI 1.15-2.56), and Strain Index scores >/= 7 (OR 1.82, CI 1.04-3.18) were associated with distal upper extremity disorders in the dominant hand. HAL repetition ratings >/= 4 (OR 2.81, CI 1.40-5.62) and hand/wrist posture ratings (OR 1.59, CI 1.01-2.49) were associated with disorders in the nondominant hand. These findings show moderate to good inter-rater agreement and significant relationships to health outcomes for the identified measures.

Evaluating ergonomic stresses in North Carolina commercial crab pot and gill net fishermen

There are challenges in evaluating physical demands of commercial fishing, including identifying sources of exposure variability. Low back biomechanical stresses associated with crab pot and gill net fishing were estimated; the variability was partitioned between and within fishing type, crew size, job title, and worker to improve understanding of risk factors for low back injury. The authors observed 162 person-hours of work among 25 North Carolina commercial fishermen on 16 crews. Postures and forces during fishing tasks were measured through direct and indirect observation using two methods to determine the percentage of time fishermen were exposed to high levels of low back stress. A multilevel linear model estimated exposure variability for the dependent variables by four nesting variables: fishing type, crew size, job title, and worker. Fishermen set and pulled crab pots or gill nets for 80% of the workday. Twenty-five percent of that time was spent handling gear. For both fishing types, handling heavy loads produced high peak compression values (3586 N to 5315 N) and high NIOSH lifting index values (3.3 to 5.4), but these tasks represent a small percentage of the overall work time (0 to 14%). The majority of exposure variation in non-neutral trunk posture and/or force > 9 kg, handling materials, NIOSH Lifting Index > 1, and Lumbar Motion Monitor probability of high-risk group membership > 70% was accounted for by fishing type (range 60 to 91%). Crew size was not an important source of variability for these six variables when fishing type and job title were accounted for in the model; but in the model restricted to crab pot fishing, crew size accounted for 51 to 88% of the variability in low back stress. For both models, job title comprised the majority of exposure variability for NIOSH Lifting Index > 3.0 (46 and 65%) and worker comprised the majority of variability for spine compression > 3400 N (54 and 65%). The magnitude and duration of musculoskeletal loads experienced by fishermen vary by the type of fishing and the tasks performed by the worker. Understanding this variability may help researchers target ergonomic interventions for this work population.

Two posture analysis approaches and their application in a modified rapid upper limb assessment evaluation

This paper presents two posture risk quantification methods: first, an event-based method where the most common and the worst postures are estimated in a task; second, a time-based method where posture distributions are calculated from random samples of observed postures in the task. A 'click-on-screen' posture data entry method was developed for the time-based posture analysis method to make the observation process easier and to reduce possible posture categorization bias. Both methods were used to quantify various work posture parameters among a study cohort of 733 subjects from a prospective epidemiological study of upper extremity musculoskeletal disorders. Composite posture indices using a modified Rapid Upper Limb Assessment (RULA) method were also computed using data obtained by the two posture analysis methods. Results showed that both methods were able to distinguish jobs with large differences in certain posture measures. However, they did not produce the same results and could not be used interchangeably. Risk evaluation criteria should be developed, either for specific posture parameters or as a composite index, with a well-defined postural analysis method, so that users can follow exact procedures and obtain comparable results. The event-based method is easy to use and may suit practitioners better, while the time-based method adds more information to the measurement and may suit users who want more detailed information about posture exposure.

Measuring low back injury risk factors in challenging work environments: an evaluation of cost and feasibility

BACKGROUND

Measuring low back injury risk factors in field research presents challenges not encountered in laboratory environments.

METHODS

We compared the practical application of five measurement methods (observations, interviews, electromyography (EMG), inclinometry, and vibration monitoring) for 223 worker days in 50 heavy-industry worksites in western Canada. Data collection successes, challenges, costs, and data detail were documented for each method.

RESULTS

Measurement success rates varied from 42.2% (seatpan accelerometer) to 99.6% (post-shift interview) of worker days assessed. Missed days for direct monitoring equipment were primarily due to explosive environments, workplace conditions likely to damage the equipment, and malfunctions. Costs per successful measurement day were lowest for interviews (approximately 23 dollars), about 10-fold higher for observations and inclinometry, and more than 20-fold higher for EMG and vibration monitoring.

CONCLUSIONS

Costs and successful field performance need to be weighed against the added data detail gained from monitoring equipment when making choices about exposure assessment techniques for epidemiological studies.

The effects of container size, frequency and extended horizontal reach on maximum acceptable weights of lifting for female industrial workers

In the development of our present manual materials handling (MMH) guidelines (Snook, S.H., Ciriello, V.M., 1991. The design of manual tasks: revised tables of maximum acceptable weights and forces. Ergonomics 34, 1197-1213), the assumption was made that the effects of frequency on maximum acceptable weights (MAWs) of lifting with a large box (hand distance, 38 cm from chest) were similar to that of lifting with a small box (hand distance, 17 cm from chest). The first purpose of the present experiment was to investigate this assumption with female industrial workers. The second purpose was to study the effects of extended horizontal reach lifting (hand distance, 44.6 cm from chest) on MAWs as a confirmation of the results of a previous studies on this variable with males (Ciriello, V.M., Snook, S.H., Hughes, G.J., 1993. Further studies of psychophysically determined maximum acceptable weights and forces. Hum. Factors 35(1), 175-186; Ciriello, V.M., 2003. The effects of box size, frequency, and extended horizontal reach on maximum acceptable weights of lifting. Int. J. Ind. Ergon. 32, 115-120). Lastly, we studied the effects of high frequency (20 lifts/min) on MAWs of lifting. Ten female industrial workers performed 15 variations of lifting using our psychophysical methodology whereby the subjects were asked to select a workload they could sustain for 8h without "straining themselves or without becoming unusually tired weakened, overheated or out of breath". The results confirmed that MAWs of lifting with the large box was significantly effected by frequency. The frequency factor pattern in this study was similar to the frequency pattern from a previous study using the small box (Ciriello, V.M., Snook, S.H., 1983. A study of size distance height, and frequency effects on manual handling tasks. Hum. Factors 25(5), 473-483) for all fast frequencies down to one lift every 2 min with deviations of 7%, 15%, and 13% for the one lift every 5 and 30 min tasks and the one lift in 8h task, respectively. The effects of lifting with an extended horizontal reach decreased MAW 22% and 18% for the mid and center lift and the effects of the 20 lifts/min frequency resulted in a MAW that was 47% of a 1 lift/min MAW. Incorporating these results in future guidelines should improve the design of MMH tasks for female workers.

Psychophysically determined horizontal and vertical forces of dynamic pushing on high and low coefficient of friction floors for female industrial workers

The purpose of this experiment was to investigate horizontal and vertical components of maximum acceptable initial and sustained forces while performing pushcart tasks on high and low coefficient of friction (COF) floors. Eleven female industrial workers performed two sessions of 120 pushcart tasks on a high COF (.68) floor and one session of 120 pushcart tasks on a low COF (.26) floor. Each pushcart task was 7.6 meters long and initiated once a minute. A psychophysical methodology was employed whereby the workers were asked to select a work load they could sustain for 8 hours without "straining themselves or without becoming unusually tired, weakened, overheated, or out of breath." The results revealed that maximum acceptable weights of the pushcart task on the low COF floor were significantly lower (20%) than the maximum acceptable weights on the high COF floor, which coincided with a significant reduction in the initial and sustained horizontal forces of push (28% and 29%, respectively) on a low COF floor. Push durations on the low COF floor were also significantly longer (36%) than on the high COF floor. Vertical forces and ratios of the vertical to horizontal forces were not significantly different comparing both floors. Calculated probabilities of slipping were supported by observations of repeated slipping by some workers during pushing on the low COF floor. Ergonomic strategies should include the maintenance of sufficient COF on floors to maximize the psychophysical pushing capabilities of the industrial worker.

Reviewing ambulance design for clinical efficiency and paramedic safety

This study aimed to review the layout of the patient compartment in a UK ambulance for paramedic efficiency and safety using: (1) link analysis; (2) postural analysis. Paramedics were observed over 16 shifts (130 h) carrying out a range of clinical tasks. The most frequently occurring clinical tasks were checking blood oxygen saturation, oxygen administration, monitoring the heart and checking blood pressure. Access to the equipment and consumables to support these tasks had been designed for the attendant seat (head end of the stretcher), however, a link analysis found that paramedics preferred to sit along side the stretcher which resulted in increased reach distances. The higher frequency tasks were found to include over 40% of working postures which required corrective measures. It was concluded that future ambulance design should be based on an ergonomics analysis (including link analysis and postural analysis) of clinical activities.

Development of risk filter and risk assessment worksheets for HSE guidance--'Upper Limb Disorders in the Workplace' 2002

Upper limb disorders (ULDs) in the workplace represent a significant cause of ill health in Great Britain. As part of the Health and Safety Commission's strategy for the prevention of musculoskeletal disorders (MSDs), the well known guidance document on ULDs--"Work-related Upper Limb Disorders: a Guide to Prevention" (HSG60), (HMSO, London.), has been extensively revised. This revision (Upper limb disorders in the workplace. HSG60 (rev), HSE Books, Sudbury.) includes the development of new risk assessment tools that can be used by employers to identify ULD risk factors in work activities and more importantly to take action to reduce or eliminate ULD risks. The risk assessment tools form part of a seven stage management approach that underpins the new guidance. This paper outlines the development of the risk assessment tools contained in the revised guidance.

Assessment of work postures and movements using a video-based observation method and direct technical measurements

The aim was to study postures and movements during repetitive work using video-based observations and direct technical measurements (inclinometers and goniometers). A total of 21 healthy women from a poultry processing plant volunteered. Neck flexion > 20 degrees was registered during 92% of the recorded time with the observation method, while the corresponding value measured with the inclinometer was 65%. Different reference positions and different measured variables apparently contributed to the differences between the methods. Mean wrist position was measured to be 0 degrees in flexion-extension and 19 degrees in ulnar deviation. Differences between the methods in the registered hand positions were small. The number of repetitive movements/minute and mean power frequency (MPF) of the electrogoniometer data was significantly related, showing both variables to be relevant measures of repetitiveness. In conclusion, the observation method and the technical measurements supplemented each other well. A reduction in class categories was suggested for future observation methods.

Validity of fixed-interval observations for postural assessment in construction work

While observing six simulated construction tasks in the field, trained analysts recorded arm, trunk and leg postures categorically with two fixed-interval observational protocols. Observations were compared to measurements obtained with an electronic postural assessment system coupled with video analysis. The electronic postural assessment system consisted of electronic inclinometers to measure upper arm posture, knee flexion and trunk flexion, coveralls to house the inclinometer wiring, and an eletrogoniometric system to measure trunk lateral bending and twisting. Video analysis included frozen-frame analysis that corresponded to the moment of observation and simulated real-time analysis. Measurements were made on five male participants who each performed three tasks representative of construction laborers' work. Agreement among the observational and reference methods was generally high, although significant differences in measured frequency of exposure existed for knee flexion, trunk lateral bending and trunk twisting. The results suggest that, under appropriate conditions, discrete observations can be used to obtain reasonably accurate estimates of exposure frequency for broad categories of certain body postures.

Comparison of self-report, video observation and direct measurement methods for upper extremity musculoskeletal disorder physical risk factors

The prevention of work-related musculoskeletal disorders has become a national priority in many countries. Increasingly, attempts are made to quantify those exposures that increase risk in order to set exposure limit values. This study used commonly employed field measurement methods and tools in order to perform an inter-method comparison between three primary methods of risk factor exposure assessment: self-report questionnaires, observational video analysis and direct measurement. Extreme posture duration, repetition, hand force (estimated from electromyography) and movement velocity were assessed for 18 subjects while performing each of three jobs processing tree seedlings. Results indicated that self-reports were the least precise assessment method, which consistently overestimated exposures for each of the measured risk factors. However, adjustment of the reports as psychophysical scales may increase agreement on a group level. Wrist flexion/extension duration and repetition were best measured by electrogoniometer. Electrogoniometric measures of wrist deviation duration and frequency were less precise than video analysis. Forearm rotation duration and repetition, grip force and velocity appeared to be best quantified by direct measurement as measured by electrogoniometer and electromyography (EMG) (as root-mean-square amplitude). The results highlight the fact that it is as important to consider and report estimated measurement error in order to reduce potential exposure misclassification in epidemiologic studies.

Questioning validity in the area of ergonomics/human factors

This paper focuses on the analysis of deviation in findings within ergonomics/human factors (E/HF) research. The current terms used to address the analysis of deviation in empirical research revolve around the notion of validity. In E/HF research papers, 'validity' is widely interpreted and includes its common parlance usage. More importantly, analysis frequently limits 'validation' to the equivalent of 'verification', eventually resulting in 'validity' as a label of little significance. To clarify the analysis of deviation, 'investigative syntaxes' are introduced to show what exactly should or can be questioned when deviation is observed, i.e. either empirical findings or propositions, and how this questioning can be structured. The possibility is discussed that, with or without the help of these syntaxes, validation may become a method of inquiry; a productive means of generating significant theoretical questions which bear directly on empirical work.

Current techniques for assessing physical exposure to work-related musculoskeletal risks, with emphasis on posture-based methods

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.

Maximum acceptable forces of dynamic pushing: comparison of two techniques

The purpose of this experiment was to investigate maximum acceptable initial and sustained forces while performing a push of 7.6 m, performed at a frequency of 1 push min-1 on a magnetic particle brake treadmill and a high-inertia push-cart. Eight male industrial workers performed a 40 min treadmill pushing task in the context of a larger experiment and two, 2 h push-cart tasks with a unique water loading system. A psychophysical methodology was employed, whereby the subjects were asked to select a workload they could sustain for 8 h without straining themselves or without becoming unusually tired, weakened, overheated or out of breath. The results revealed that maximum acceptable initial and sustained forces of pushing on the high inertia cart were significantly higher (28 and 23%, respectively) than pushing forces on the magnetic particle brake treadmill. It was concluded that adjustments to the pushing and pulling data bank by Snook and Ciriello (1991) may be appropriate if verification of this experiment yields similar results.

Validation of Portable Ergonomic Observation (PEO) method using optoelectronic and video recordings

The validity of the 'Portable Ergonomic Observation' method (PEO) was investigated against posture measurements based on continuous optoelectronic and video recordings made simultaneously with the observation. Work postures and actions during different frequently changing tasks were analyzed using both methods. In general, a high agreement between measured and observed data was achieved for the duration of clearly identifiable sustained postures and actions (such as repetitive movements of hands when typing), as well as for the frequency of clearly distinguishable actions (such as lifts). The agreement between observations and measurements was low for neck postures. In dynamic tasks the agreement was generally low. This was probably because of high levels of simultaneous information for the observer. No improvement in the agreement between measured and observed events could be achieved by leaving parts of the PEO categories unobserved at a time. Playback of video tapes to observe each category separately would increase the reliability of the observations but at the expense of increased time for the analysis.

Arm and trunk posture during work in relation to shoulder and neck pain and trapezius activity

OBJECTIVE: To investigate work technique in relation to work-related shoulder and neck pain (SNP) and upper trapezius muscle activity. DESIGN: A matched pair, case-control field study of female employees with and without SNP. BACKGROUND: It has proved difficult to distinguish subjects with SNP from those without by vocational electromyographic recordings from the upper trapezius muscle. Other potential risk indicators include psychosocial factors and work technique. This study focuses on the latter. METHODS: Manual (14 pairs) and office workers (24 pairs) were recorded during a 30-min work period. Simultaneous recordings of upper trapezius activity by surface electromyography and arm and upper back postures by inclinometers were analysed. RESULTS: Cases and controls were not differentiated on the basis of arm elevation or of trunk posture in the sagittal plane. No significant correlations were found between variables averaging the muscle activity and the arm elevation over the recording period. Statistically significant correlations were, however, found between these variables when analysing recordings at high time resolution (0.2 s) and adjusting for the delay in arm elevation relative to the upper trapezius muscle activity (r = 0.43, manual group; r = 0.32, office group). CONCLUSIONS: Factors other than arm elevation probably contribute more significantly to the load in the upper trapezius muscle, and to the development of work-related SNP in work situations with moderate arm elevation. RELEVANCE: The study suggests that arm and trunk posture recordings are not a sensitive indicator of risk of shoulder and neck complaints in work with low to moderate biomechanical demands.

A video-based method for evaluation of low-back load in long-cycle jobs

A method for evaluation of the physical load on the lumbar spine in industrial work is presented. It is suitable for identification of high spinal loads and their time duration. The method is based on biomechanical analysis of video-recordings. It takes into account the posture of the body as such, as well as the possible occurrence of external load and support. Compression of the L5-S1 intervertebral disc and strain on the lumbodorsal fascia is determined at 5-s intervals in each work task.

A portable ergonomic observation method (PEO) for computerized on-line recording of postures and manual handling

A new portable ergonomic observation method (PEO) is presented. It is applicable to most professions and work tasks and requires only moderate human resources for data collection and analysis. Observations are made in real time directly at the workplace using a portable personal or hand-held computer, and data are accessible for immediate analysis and presentation. Duration and number of events are calculated for postures at four body regions (arms, neck, trunk and knee) as well as for manual handling. An evaluation of the PEO method, assessing some important aspects of internal validity as well as intra- and inter-observer reliability, was carried out using video recordings. It showed acceptable validity for some types of physical exposure, and high intra- and inter-observer reliability. Practical experiences from using the PEO method in a field study and further improvements of the method are discussed.

Direct measurements and systematic observations of physical workload among medical secretaries, furniture removers and male and female reference populations

The aim of this investigation was to collect quantitative information about the occurrence of manual materials handling and working postures in working life. Direct technical recordings and systematic observations by trained ergonomists were used throughout a whole working day on 12 male furniture removers, 13 female medical secretaries, 27 males and 45 females randomly sampled from the working population in the Stockholm area. A quantitative job exposure profile was obtained by weighting together exposure data obtained by observation of tasks occurring during a normal working week. The results showed no major differences in physical exposures between the male and female reference populations. The medical secretaries spent less time than the female population kneeling/squatting and longer time than any other group with repetitive hand movements. Exposure data for task and job should be clearly distinguished.