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  • 1.
    Coenen, Pieter
    et al.
    Vrije Universiteit Amsterdam, Department of Public and Occupational Health, Amsterdam Public Health Research Institute, Amsterdam, The Netherlands.
    van der Beek, Allard J.
    Vrije Universiteit Amsterdam, Department of Public and Occupational Health, Amsterdam Public Health Research Institute, Amsterdam, The Netherlands.
    Jackson, Jennie
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbetshälsovetenskap och psykologi, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Mathiassen, Svend Erik
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbetshälsovetenskap och psykologi, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Calibration of self-reported physical behaviours among office workers: A compositional data analysis2019Inngår i: ICAMPAM 2019: Oral Abstracts, Maastricht: ICAMPAM , 2019, artikkel-id O.11.2Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The aim of this study was to develop and evaluate calibration models to predict objectively measured time spent sitting, standing and walking during office work from self-reported time-use compositions using a compositional data analysis (CoDA) approach. Ninety-nine office workers (49 women) at the Swedish Transport Administration participated in an intervention study on relocation to activity-based offices. At baseline and at a 3-months follow-up, physical behaviours (sitting, standing and walking) at work were assessed for five days using a thigh-mounted accelerometer (Actigraph) and by self-report (IPAQ). The time-use composition of the three behaviours was expressed in terms of isometric log-ratios (ILR). Calibration models predicting accelerometry-based time-use from self-reported compositions were constructed using linear regression on baseline data, and then validated using follow-up data. The accelerometer data showed that, on average, workers spent 69.9% of their day sitting, 23.7% standing, and 6.4% walking. The corresponding percentages for self-reports were 71.7%, 21.6%, and 7.4%, respectively. Non-calibrated self-reports were biased: the RMS errors obtained from the ILRs expressing sitting, standing and walking were 0.73, 1.09 and 1.05, respectively. Calibration models reduced these errors by 45% (sitting), 56% (standing), and 76% (walking). Validation of the calibration models using follow-up data from the same workers showed calibration remained equally effective; RMS errors were reduced by 55% (sitting), 58% (standing), and 75% (walking). In conclusion, calibration models for compositional time-use data were effective in reducing bias in self-reported physical behaviours at work, and the models remained effective when used on new data from the same workers. Calibrated self-reports may represent a cost-effective method for obtaining physical behaviour data with a satisfying accuracy in large-scale cohort and intervention studies.

  • 2.
    Dempsey, Patrick G.
    et al.
    Liberty Mutual Research Institute for Safety, Massachusetts, USA.
    Mathiassen, Svend Erik
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, CBF. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Jackson, Jennie A.
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, CBF. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    O'Brien, Niall V
    Liberty Mutual Research Institute for Safety, Hopkinton MA, USA.
    Influence of three principles of pacing on the temporal organisation of work during cyclic assembly and disassembly tasks2010Inngår i: Ergonomics, ISSN 0014-0139, E-ISSN 1366-5847, Vol. 53, nr 11, s. 1347-1358Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A study was conducted to investigate the influence of different approaches to arranging the pace and temporal organisation of repetitive assembly and disassembly tasks on both average performance and its variability and to compare assembly and disassembly times derived with psychophysical methods to a more traditional methods-time measurement (MTM) approach. The conditions studied were a traditional assembly line arrangement, where assemblies were started at a pace of 110 MTM (repeated on two occasions), a batch condition, where subjects were required to complete 36 assemblies within the total amount of time allowed at 110, MTM and a psychophysical condition, where subjects were allowed to choose their pace (repeated on two occasions). Overall, the results suggest that the mean time spent working in each cycle (the 'on-time') remained fairly constant across conditions, while the idle 'off-time' in between on-times was shorter and of less varied duration in the more autonomous batch and psychophysical conditions. During the second psychophysical (self-paced) condition, subjects completed a significantly higher number of assemblies than during the 110 MTM line condition. The higher pace was achieved through reduction in mean off-times and the potential implications for musculoskeletal risk are discussed. Statement of Relevance: Higher levels of autonomy over work pace, which intuitively would be beneficial from an ergonomics standpoint, actually led to subjects selecting to organise work such that off-times (idle times) were reduced. In contrast, active 'on' times were not affected much by autonomy. These results point to a reason that piecework would be associated with increased risk for musculoskeletal disorders.

  • 3.
    Hallman, David
    et al.
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbetshälsovetenskap och psykologi, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Mathiassen, Svend Erik
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbetshälsovetenskap och psykologi, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    van der Beek, Allard
    Department of Public and Occupational Health, Amsterdam UMC, Vrije Universiteit Amsterdam.
    Jackson, Jennie
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbetshälsovetenskap och psykologi, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Coenen, Pieter
    Department of Public and Occupational Health, Amsterdam UMC, Vrije Universiteit Amsterdam.
    Calibration of self-reported time spent sitting, standing and walking among office workers: a compositional data analysis2019Inngår i: International Journal of Environmental Research and Public Health, ISSN 1661-7827, E-ISSN 1660-4601, Vol. 16, nr 17, artikkel-id 3111Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We developed and evaluated calibration models predicting objectively measured sitting, standing and walking time from self-reported data using a compositional data analysis (CoDA) approach. A total of 98 office workers (48 women) at the Swedish Transport Administration participated. At baseline and three-months follow-up, time spent sitting, standing and walking at work was assessed for five working days using a thigh-worn accelerometer (Actigraph), as well as by self-report (IPAQ). Individual compositions of time spent in the three behaviors were expressed by isometric log-ratios (ILR). Calibration models predicting objectively measured ILRs from self-reported ILRs were constructed using baseline data, and then validated using follow-up data. Un-calibrated self-reports were inaccurate; root-mean-square (RMS) errors of ILRs for sitting, standing and walking were 1.21, 1.24 and 1.03, respectively. Calibration reduced these errors to 36% (sitting), 40% (standing), and 24% (walking) of those prior to calibration. Calibration models remained effective for follow-up data, reducing RMS errors to 33% (sitting), 51% (standing), and 31% (walking). Thus, compositional calibration models were effective in reducing errors in self-reported physical behaviors during office work. Calibration of self-reports may present a cost-e_ective method for obtaining physical behavior data with satisfying accuracy in large-scale cohort and intervention studies.

  • 4.
    Jackson, Jennie A.
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning. Uppsala universitet.
    Bias and Precision in Biomechanical Exposure Assessment: Making the Most of our Methods2017Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Background: Insufficient exposure assessment is a suggested contributing factor to the current lack of clearly characterised relationships between occupational biomechanical risk factors and musculoskeletal disorders. Minimal attention has been paid to the potential bias of measurement tools from expected true values (i.e. accuracy) or between measurement tools, and empirical data on the magnitudes of variance contributed by methodological factors for measurement tool precision are lacking.

    Aim: The aim of this thesis was to quantify aspects of bias and precision in three commonly employed biomechanical risk factor assessment tools - inclinometry, observation, and electromyography (EMG) - and provide recommendations guiding their use. Methods: Upper arm elevation angles (UAEAs) were assessed using inclinometers (INC) and by computer-based posture-matching observation, and bias relative to true angles was calculated. Calibration models were developed for INC data, and their efficacy in correcting measurement bias was evaluated. The total variance of trapezius and erector spinae (ES) EMG recordings during cyclic occupational work was partitioned into biological and methodological sources, including the variance uniquely attributable to sub-maximal normalisation. Using algorithms to estimate the precision of a group mean, the efficacy of different trapezius EMG study designs was evaluated. Using precision criteria, the efficacy of different normalisation methods was assessed for ES EMG recordings.

    Results and Discussion: Inclinometer measured UAEAs were biased from true angles, with increasing bias at higher angles. In contrast, computer based posture-matching observations were not biased from true angles. Calibration models proved effective at minimizing INC data bias. The dispersion of estimates between- and within- observers at any given set angle underlined the importance of repeated observations when estimating UAEAs. For EMG, a unique but relatively small component of the total variance was attributable to the methodological process of normalisation. Performing three repeats of the trapezius EMG normalisation task proved optimal at minimizing variance for one-day EMG studies, while two repeats sufficed for multi-day EMG studies. A prone normalisation task proved superior for maximizing normalised lumbar ES EMG precision.

    Conclusion: Key aspects of measurement tool accuracy, bias between tools, and tool precision were quantified, and recommendations were made to guide future research study design.

  • 5.
    Jackson, Jennie A.
    et al.
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Mathiassen, Svend Erik
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Callaghan, Jack
    Department of Kinesiology, University of Waterloo, Ontario, Canada.
    Dempsey, Patrick
    National Institute for Occupational Safety and Health, Pittsburgh, USA.
    Precision based guidelines for sub-maximal normalisation task selection for trunk extensor EMG2017Inngår i: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 37, s. 41-51Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Aim: The object of this study was to quantify the contribution of sub-maximal normalisation to the overall variance of exposure parameters describing erector spinae (ES) activity, and to provide guidelines for task selection which minimize methodological variance. Methods: ES EMG was measured from three locations (T9, L1 and L5 levels) on fifteen men performing a manual materials handling task in the laboratory on three separate days. Four repeats of each of eleven sub-maximal normalisation tasks (eight static, three dynamic) were collected, work data were normalised to each task and repeat, and exposure parameters calculated. The unique contribution of normalisation to the overall variance was determined for each task and exposure parameter using variance component analyses. Normalisation tasks were scored according to their relative contributions to the overall variance and coefficients of variation.

    Results: A prone task, similar to the Biering-Sørensen test posture, was the most repeatable for all electrode locations and across all exposure parameters. Thoracic level normalisation typically showed poorer repeatability than lumbar normalisation.

    Discussion: We recommend that future ES EMG studies employing sub-maximal normalisation utilise said prone task. An alternate normalisation task specific to thoracic level ES muscles may be warranted.

  • 6.
    Jackson, Jennie A
    et al.
    Högskolan i Gävle, Centrum för belastningsskadeforskning. Department of Kinesiology, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada ; Liberty Mutual Research Institute for Safety, Hopkinton, USA.
    Mathiassen, Svend Erik
    Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Dempsey, Patrick G.
    Liberty Mutual Research Institute for Safety, Hopkinton, USA.
    Methodological variance associated with normalization of occupational upper trapezius EMG using submaximal reference contractions2009Inngår i: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 19, nr 3, s. 416-427Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Objectives: To quantify the variance introduced to trapezius electromyography (EMG) through normalization by submaximal reference voluntary exertions (RVE), and to investigate the effect of increased normalization efforts as compared to other changes in data collection strategy on the precision of occupational EMG estimates. Methods: Women performed four RVE contractions followed by 30 minutes of light, cyclic assembly work on each of two days. Work cycle EMG was normalized to each of the RVE trials and seven exposure parameters calculated. The proportions of exposure variance attributable to subject, day within subject, and cycle and normalization trial within day were determined. Using this data, the effect on the precision of the exposure mean of altering the number of subjects, days, cycles and RVEs during data collection was simulated. Results: For all exposure parameters a unique component of variance due to normalization was present, yet small: less than 4.4% of the total variance. The resource allocation simulations indicated that marginal improvements in the precision of a group exposure mean would occur above three RVE repeats for EMG collected on one day, or beyond two RVEs for EMG collected on two or more days.

  • 7.
    Jackson, Jennie A.
    et al.
    Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Mathiassen, Svend Erik
    Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Dempsey, Patrick G.
    Liberty Mutual Research Institute for Safety, Hopkinton MA, USA.
    Methodological variance associated with normalization of trapezius EMG using submaximal reference contractions2006Inngår i: Proceedings of the 16th World Congress of the International Ergonomics Association / [ed] Ernst Koningsveld, 2006Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    While electromyography (EM G) is commonly used to quantify levels of muscle activity in different jobs and tasks, less attention has been paid to the size and sources of exposure variability between and within individuals at work. In particular , few attempts have been made to discriminate between biological sources of variabilityand methodological uncertainty, including the effects of the EMG normalization procedure. The present study aimed to quantify the testretest repeatability of reference voluntary effort (R VE) contractions of the upper trapezius and the amount of variance introduced to EMG exposure parameters due to normalization trial variance.

    EMG data was collected from the right trapezius muscle of 15 female subjects during 36 work cycles of simulated industrial assembly work on t wo separate days. For all cycles, EMG was norrnalized to each of the four RVE calibration trials collected on the day. From the normalized data the following exposure parameters were calculated for all cycles and norrnalizations: 1 St, 10th, 50th, 90th, and 99th percentile APDF values; mean EMG amplitude; time spent at 'rest' « 6.7% RVE); and time spent at 'large activation levels' (> 100% RVE). Exposure variability due to subjects, day within subject, work cycle within day, and normalization trial was determined using a variance component analysis based on ANOV A algorithms. For all parameters, the dominate source of variance occurred between subjects. For all parameters, except the 1 st APDF percentile and the time spent at rest, the proportions of variance due to norrnalization and cycle were no more than 5% of the sum of all variance components. The betweenday variance for mean and all APDF parameters besides the 1 st APDF percentile ranged from 7 -19% of the total variance, indicating changes in work style or activation patters between days do exist. The effects of normalization reported here are likely at the low end of the range (test-retest coefficient of variation = 0.07) compared to the expected effects when data are collected in the field using less meticulously controIled RVE trials.

  • 8.
    Jackson, Jennie A.
    et al.
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Mathiassen, Svend Erik
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Liv, Per
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning. Centre for Research and Development, Uppsala University/Region Gävleborg, Gävle.
    Observer performance in estimating upper arm elevation angles under ideal viewing conditions when assisted by posture matching software2016Inngår i: Applied Ergonomics, ISSN 0003-6870, E-ISSN 1872-9126, Vol. 55, s. 208-215Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Selecting a suitable body posture measurement method requires performance indices of candidate tools. Such data are lacking for observational assessments made at a high degree of resolution. The aim of this study was to determine the performance (bias and between- and within-observer variance) of novice observers estimating upper arm elevation postures assisted by posture matching software to the nearest degree from still images taken under ideal conditions. Estimates were minimally biased from true angles: the mean error across observers was less than 2°. Variance between observers was minimal. Considerable variance within observers, however, underlined the risk of relying on single observations. Observers were more proficient at estimating 0°and 90° postures, and less proficient at 60°. Thus, under ideal visual conditions observers, on average, proved proficient at high resolution posture estimates; further investigation is required to determine how non-optimal image conditions, as would be expected from occupational data, impact proficiency.

  • 9.
    Jackson, Jennie A.
    et al.
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Mathiassen, Svend Erik
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Srinivasan, Divya
    Grado Department of Industrial and Systems Engineering, Virginia Polytechnic Institute and State University.
    Identification of individual working styles in a long-cycle assembly task using kinematic and EMG variables2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Background.Increased motor variability while performing repetitive tasks has been suggested to decrease the risk of developing musculoskeletal disorders. However, support for this positive effect is lacking outside of short, simple, highly controlled tasks. It is also currently unknown whether or not existing motor variability metrics are viable for characterising occupational tasks. The purpose of this study was to assess motor variability during a long-cycle simulated occupational task. Using metrics previously validated for short-cycle tasks, this study aimed to determine the extent to which: (1) individuals dif-fered in motor variability with respect to kinematics and/or EMG activation; (2) individual motor variability was consistent across days; and (3) kinematics and EMG motor variability were correlated.

    Methods.Following a stringent, three-day training regime, 15 females proved sufficiently proficient to participate. On two occasions, participants performed 36 cycles of an assembly task (combining gross and fine motor skills) at 110 MTM pacing (51 s per cycle). For each cycle, multiple upper arm kinematic and trapezius EMG summary mean and SD variables were calculated; for each variable, the variability across the 36 cycles was assessed. The relative size of variability across individuals, and the consistency of each individual’s motor behaviour across days were assessed using kinematic and EMG vari-ables. The correlation between kinematic and EMG variables was also assessed.

    Results.Distinct individual behaviours were observed across days: some participants were clearly more consistent in their motor behaviour than others. Further, a high correlation was found between some kinematic and muscle activation variables.

    Discussion. Using previously validated upper arm assessment metrics, we were able to differentiate between individuals performing a long-cycle assembly task based on their degree of motor variability. Given the nature of our study task, we believe the metrics that we found to be successful at identifying individual behaviours could be used for assessing field tasks.

  • 10.
    Jackson, Jennie
    et al.
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning. Uppsala University.
    Banerjee-Guénette, Priyanka
    University of Waterloo, Department of Kinesiology, Faculty of Applied Health Sciences.
    Gregory, Diane
    Wilfrid Laurier University, Health Sciences Program and Department of Kinesiology.
    Callaghan, Jack
    University of Waterloo, Department of Kinesiology, Faculty of Applied Health Sciences.
    Should we be more on the ball?: The efficacy of accommodation training on lumbar spine posture, muscle activity, and perceived discomfort during stability ball sitting2013Inngår i: Human Factors, ISSN 0018-7208, E-ISSN 1547-8181, Vol. 55, nr 6, s. 1064-1076Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Objective: To evaluate the efficacy of a nine-day accommodation protocol on reducing perceived discomfort while sitting on a stability ball (SB); trunk muscle activity levels and lumbar spinal postures were also considered.

    Background: Previous studies have compared SB sitting to office chair sitting with few observed differences in muscle activity or posture; however, greater discomfort during SB sitting has been reported.  These findings may indicate an accommodation period is necessary to acclimate to SB sitting.

    Methods: Six males and six females completed two separate, two-hour sitting sessions on an SB.  Half the participants completed a nine-day accommodation period between the visits while the other half did not use an SB during the time. On both occasions, self-reported perceived discomfort ratings were collected along with erector spinae and abdominal muscle activity and lumbar spinal postures.

    Results: Discomfort ratings were reduced in female participants following the accommodation; no effects on muscle activation or lumbar spine postures were observed.

    Conclusion: Accommodation training may reduce perceived low back discomfort in females. Trunk muscle activity and lumbar spine postures during seated office work on an SB did not differ between groups; however, greater sample power was required to conclusively address these variables.

    Application: When deciding whether to use an SB in place of a standard office chair, this study indicates females electing to use an SB can decrease discomfort by following an accommodation protocol; no evidence was found to indicate SB chair use will improve trunk strength or posture, even following an accommodation period. 

  • 11.
    Jackson, Jennie
    et al.
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Forsman, Mikael
    Institutet för miljömedicin, Karolinska institutet, Stockholm.
    Heiden, Marina
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Waleh Åström, Amanda
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Mathiassen, Svend Erik
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Symposium: Measuring posture in working life: Observation or inclinometry? [Mätning av arbetsställningar: observation eller inklinometri?]2018Inngår i: FALF KONFERENS 2018 Arbetet – problem eller potential för en hållbar livsmiljö?   10-12 juni 2018 Gävle: Program och abstracts / [ed] Lindberg, Per, Gävle: Gävle University Press , 2018, s. 38-40Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Quantifying postures during work is a key aspect of understanding the physical loads experienced by the body at work. Two commonly used tools to assess posture are observation and inclinometry. Observation can be performed in many ways, from real-time observations made at the worksite assessing gross body postures, to estimates of individual joint angles made by observers assessing still images taken from video recorded at the work site. Inclinometry is a direct technical measurement tool which typically uses tri-axial accelerometers to determine angles of specific body segments with respect to the line of gravity. Regardless of which tool is used, it will introduce some variability between repeated measurements of a same posture – this is called method-logical variability. Over the past ten years we have worked extensively in our Cost-efficient measurement of physical exposures research program to quantify the magnitude of error resulting from different measurement strategies – both in terms of bias (that is, the difference between the truth and the measured values) and precision (that is, how different repeated estimates of a same posture are). Further, we have compared the monetary costs and relative performances (in terms of measurement quality) of different measurement strategies. From these studies we have developed a set of recommendations to guide effective posture assessment.

    We assessed bias in both observation and inclinometry to determine how close posture estimates were to the true body segment angles. Under ideal observation conditions, observers were not biased in estimating upper arm elevation angles (1). Conversely, we found a systematic underestimation of upper arm elevation angles made using inclino-metry, particularly for angles at or above 60° (2). We developed a simple, on-body incli-nometry calibration procedure, and determined it was effective at reducing inclinometer bias (2).

    We investigated how data sampling should be distributed within and across days, and how much data was required to obtain a specific level of precision. Regardless of the tool, we found that efficiency was improved by distributing shorter sampling periods using a fixed-interval strategy across an entire day or days rather than collecting one longer period (3,4). Precision of inclinometer data is high and thus a single measurement of an event is sufficient. In contrast, observation requires repeated estimates of an image, even under ideal conditions (1, 5). For observation of still images from videos, we determined that efficiency was improved by assessing images extracted at set intervals across the recorded data (i.e. a work sampling approach) rather than making estimates based on continuously viewed intervals of video data (5). Further, repeated observations by one or more observers of a smaller number of frames of data improved the precision of angle estimates compared with a single observer rating a larger number of frames (6). In the case that a worker is obstructed from the camera view, additional frame analysis may be required and the uncertainty of the angle estimate may increase (7).

    We developed models to assess the net cost of each method, including equipment acquisition, data collection and data analysis. While the initial expense may seem higher for inclinometers, cost gains are made during collection and analysis stages compared to the work-intensive post-collection efforts required for observation. We found that inclinometry was more cost efficient than observation in certain settings (8), but that uncertainty exists even in cost assessment models and thus that cost-efficiency is situation-dependent (9).

    There are strengths and weaknesses to both tools and one must evaluate the goals of each data collection and the relative merits of each tool when determining the appropriate assessment method. Observation may be preferable for studies seeking a general impression of a working day, identifying the tasks comprising a working day, assessing twisting during work, or assessing whether anatomical segments are loaded or supported during work. Inclinometers may be preferred for studies requiring full day or multi-day assessments, a high degree of accuracy and precision in angle estimates, information on segmental movement velocities, and/or studies where workers cannot be adequately filmed. Rapid advances in inclinometer technology and smart phone analogues will serve to further minimise set-up times and acquisition costs, making direct technical measurement increasingly feasible.

    1. Jackson, J. A., Mathiassen, S. E. & Liv, P. Observer performance in estimating upper arm elevation angles under ideal viewing conditions when assisted by posture matching software. Appl. Ergon. 55, 208–215 (2016).

    2. Jackson, J. A., Mathiassen, S. E., Wahlström, J., Liv, P. & Forsman, M. Is what you see what you get? Standard inclinometry of set upper arm elevation angles. Appl. Ergon. 47, 242–252 (2015).

    3. Liv, P., Mathiassen, S. E. & Svendsen, S. W. Theoretical and empirical efficiency of sampling strategies for estimating upper arm elevation. Ann. Occup. Hyg. 55, 436–449 (2011).

    4. Liv, P., Mathiassen, S. E. & Svendsen, S. W. Accuracy and precision of variance components in occupational posture recordings: A simulation study of different data collection strategies. BMC Med. Res. Methodol. 12, 58–68 (2012).

    5. Rezagholi, M., Mathiassen, S. E. & Liv, P. Cost efficiency comparison of four video-based techniques for assessing upper arm postures. Ergonomics 55, 350–360 (2012).

    6. Liv, P., Mathiassen, S. E. & Wahlström, J. Statistical power and measurement requirements in studies comparing observed postures between groups. (PhD Thesis, Umeå University, 2012).

    7. Trask, C., Mathiassen, S. E., Rostami, M. & Heiden, M. Observer variability in posture assessment from video recordings: The effect of partly visible periods. Appl. Ergon. 60, 275–281 (2017).

    8. Trask, C., Mathiassen, S. E., Jackson, J.A. & Wahlström, J. Data processing costs for three posture assessment methods. BMC Med. Res. Methodol. 13, 124–137 (2013).

    9. Waleh Åström, A., Heiden, M., Mathiassen, S. E. & Strömberg, A. Uncertainty in monetary cost estimates for assessing working postures using inclinometry, observation or self-report. in review, (2018).

  • 12.
    Jackson, Jennie
    et al.
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, CBF. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Mathiassen, Svend Erik
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, CBF. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    The trade-off between meticulousness and methodological variance in normalization of low back EMG2012Inngår i: Work: A journal of Prevention, Assesment and rehabilitation, ISSN 1051-9815, E-ISSN 1875-9270, Vol. 41, nr Suppl. 1, s. 2307-2314Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Background: Normalization of surface electromyography (EMG) is a common and recommended practice, however this methodological step itself introduces variability to a data set. Quantification of this variance is necessary to correctly interpret overall EMG variability. This information is also paramount to identifying experimentally and clinically relevant normalization task(s) which minimize induced variance yet are time-efficient. Purpose: The goal of this study was to quantify the within-day variance of two commonly reported, sub-maximal tasks utilised for low back EMG normalization: one collected with a high degree of meticulousness, and the other collected in a more rapid manner. Results: Only minimal differences were seen between tasks in the magnitude of within-day variance for EMG amplitude at all recording sites, save the right-side L5 location, which showed a significant difference (p=0.020). For trunk posture, within-day variance for the highly meticulous tasks was significantly higher than for the less-meticulous task (p=0.011). Conclusion: A less meticulous sub-maximal normalization task performed in a standing position was equal or superior to a more meticulously collected task in terms of kinematic task repeatability and within-day EMG variance. These findings are encouraging for field study applications where meticulous methods are not feasible, and provide a time saving strategy for lab studies.

  • 13.
    Jackson, Jennie
    et al.
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Mathiassen, Svend Erik
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Wahlström, Jens
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning. Department of Public Health and Clinical Medicine, Occupational and Environmental Medicine, Umeå University, Umeå, Sweden .
    Liv, Per
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning. Centre for Research and Development, Uppsala University/County Council of Gävleborg, Gävle, Sweden .
    Forsman, Mikael
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning. Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden .
    Digging deeper into the assessment of upper arm elevation angles using standard inclinometry2015Inngår i: Applied Ergonomics, ISSN 0003-6870, E-ISSN 1872-9126, Vol. 51, s. 102-103Artikkel i tidsskrift (Annet vitenskapelig)
  • 14.
    Jackson, Jennie
    et al.
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Mathiassen, Svend Erik
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Wahlström, Jens
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning. Department of Public Health and Clinical Medicine, Umeå University.
    Liv, Per
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning. Centre for Research and Development, Uppsala University/County Council of Gävleborg.
    Forsman, Mikael
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning. Institute of Environmental Medicine, Karolinska Institutet.
    Is what you see what you get? Standard inclinometry of set upper arm elevation angles2015Inngår i: Applied Ergonomics, ISSN 0003-6870, E-ISSN 1872-9126, Vol. 47, s. 242-252Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Previous research suggests inclinometers (INC) underestimate upper arm elevation. This study was designed to quantify possible bias in occupationally relevant postures, and test whether INC performance could be improved using calibration.

    Participants were meticulously positioned in set arm flexion and abduction angles between 0° and 150°. Different subject-specific and group-level regression models comprising linear and quadratic components describing the relationship between set and INC-registered elevation were developed using subsets of data, and validated using additional data.

    INC measured arm elevation showed a downward bias, particularly above 60°.  INC data adjusted using the regression models were superior to un-adjusted data; a subject-specific, two-point calibration based on measurements at 0° and 90° gave results closest to the ‘true’ set angles.

    Thus, inclinometer measured arm elevation data required calibration to arrive at ‘true’ elevation angles. Calibration to a common measurement scale should be considered when comparing arm elevation data collected using different methods.

  • 15.
    Jackson, Jennie
    et al.
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, CBF. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Punnett, Laura
    Department of Work Environment, University of Massachusetts Lowell.
    Mathiassen, Svend Erik
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, CBF. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Statistical precision of categorical PATH observations of trunk posture2012Inngår i: Work: A journal of Prevention, Assesment and rehabilitation, ISSN 1051-9815, E-ISSN 1875-9270, Vol. 41, nr Suppl. 1, s. 5519-5521Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Background: Field studies assessing biomechanical occupational exposures frequently utilize direct observation. PATH (Postures, Activities, Tools, and Handling) is a tool for systematically observing occupational exposures during non-cyclic or long, irregular-cycle jobs. While PATH has been used in many studies, its statistical performance under different data collection strategies has not yet been investigated. The purpose of the current study was to examine this issue. Methods: Data from labourers performing the four tasks comprising a ‘Jacking Pit Construction’ operation was extracted from a previously collected data set. Using a probability based re-sampling bootstrap approach, categorical trunk posture exposure data was compared across nine simulated data collection strategies. Results/Conclusion: At the operational level, dispersion curves showed consistent trends of increased precision with increased sizes of the data set and curves tended to intersect at the expected value seen in the parent data set. At the task level, curves did not always follow the predicted pattern, highlighting the potential pitfalls of using PATH for infrequent tasks and the striking effect that individual workers can have on group exposure estimates of such tasks.

  • 16.
    Jackson, Jennie
    et al.
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbetshälsovetenskap och psykologi, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Srinivasan, Divya
    Department of Industrial and Systems Engineering, Virginia Tech, Blacksburg, Virginia, USA.
    Mathiassen, Svend Erik
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbetshälsovetenskap och psykologi, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Consistent individual motor variability traits demonstrated by females performing a long-cycle assembly task under conditions differing in temporal organisation2019Inngår i: Applied Ergonomics, ISSN 0003-6870, E-ISSN 1872-9126Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Low motor variability (MV) during repetitive work has shown association with higher risk for developing work-related musculoskeletal disorders (MSDs). Whether consistent individual MV characteristics exist across working conditions remains unknown. This study aimed to determine if individual MV traits were consistent during complex assembly work performed under conditions differing in temporal organisation.

    Fifteen women performed cyclic-assembly under four conditions differing in pace and organisation (line-type, batch-type). Variability of trapezius muscle activity and upper arm elevation was quantified. Total MV variance was partitioned into components attributable to subjects, days and conditions.

    For all metrics, a non-zero between-subjects variance was found, indicating consistent individual MV traits across conditions. Variance between subjects was higher for EMG MV metrics compared with kinematic metrics.

    Our results showed individuals exhibited consistent MV traits across working conditions differing in pace and production process, and support continued research into MV as a possible individual risk factor for MSDs.

  • 17.
    Jackson, Jennie
    et al.
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Srinivasan, Divya
    Mathiassen, Svend Erik
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Is movement variability a consistent personal trait? Kinematic evidence from long-cycle assembly work2018Konferansepaper (Fagfellevurdert)
  • 18.
    Mathiassen, Svend Erik
    et al.
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Jackson, Jennie
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Punnett, Laura
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning. Department of Work Environment, University of Massachusetts Lowell, USA.
    Statistical performance of observational work sampling for assessment of categorical exposure variables: A simulation approach illustrated using PATH data2014Inngår i: Annals of Occupational Hygiene, ISSN 0003-4878, E-ISSN 1475-3162, Vol. 58, nr 3, s. 294-316Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Objectives. Observational work sampling is often used in occupational studies to assess categorical biomechanical exposures and occurrence of specific work tasks. The statistical performance of data obtained by work sampling is, however, not well understood, impeding informed measurement strategy design. The purpose of this study was to develop a procedure for assessing the statistical properties of work sampling strategies evaluating categorical exposure variables, and to illustrate the usefulness of this procedure to examine bias and precision of exposure estimates from samples of different sizes.

    Methods. From a parent data set of observations on 10 construction workers performing a single operation, the probabilities were determined for each worker of performing four component tasks and working in four mutually exclusive trunk posture categories (neutral, mild flexion, severe flexion, twisted). Using these probabilities, 5000 simulated data sets were created via probability-based re-sampling for each of six sampling strategies, ranging from 300 to 4500 observations. For each strategy, mean exposure and exposure variability metrics were calculated at both the operation- and task-levels and, for each of these, bias and precision were assessed across the 5000 simulations.

    Results. Estimates of exposure variability were substantially more uncertain at all sample sizes than estimates of mean exposures and task proportions. Estimates at small sample sizes were also biased. With only 600 samples, proportions of the different tasks and of working with a neutral trunk posture (the most common) were within 10% of the true target value in at least 80% of all the simulated data sets; rarer exposures required at least 1500 samples. For most task-level mean exposure variables and for all operation- and task-level estimates of exposure variability, performance was low, even with 4500 samples. In general, the precision of mean exposure estimates did not depend on the exposure variability between workers.

    Conclusions. The suggested probability-based simulation approach proved to be versatile and generally suitable for assessing bias and precision of data collection strategies using work sampling to estimate categorical data. The approach can be used in both real and hypothetical scenarios, in ergonomics as well as in other areas of occupational epidemiology and intervention research. The reported statistical properties associated with sample size are likely widely relevant to studies using work sampling to assess categorical variables.

  • 19.
    Trask, Catherine
    et al.
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning. University of Saskatchewan, College of Medicine, Centre for Health & Safety in Agriculture, Saskatoon, SK S7N 0W8, Canada.
    Mathiassen, Svend Erik
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Jackson, Jennie
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Wahlström, Jens
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning. Umea University, Department of Public Health & Clinical Medical Occupational & Environmental Medicine, SE-90185 UmeåSweden.
    Data processing costs for three posture assessment methods2013Inngår i: BMC Medical Research Methodology, ISSN 1471-2288, E-ISSN 1471-2288, Vol. 13, nr 1, s. 124-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Objectives. Data processing contributes a non-trivial proportion to total research costs, but documentation of these costs is rare. This paper employed a priori cost tracking for three posture assessment methods (self-report, observation of video, and inclinometry), developed a model describing the fixed and variable cost components, and simulated additional study scenarios to demonstrate the utility of the model. 

    Methods. Trunk and shoulder postures of aircraft baggage handlers were assessed for 80 working days using all three methods. A model was developed to estimate data processing phase costs, including fixed and variable components related to study planning and administration, custom software development, training of analysts, and processing time.   

    Results. Observation of video was the most costly data processing method with total cost of 31,433, and was 1.2-fold more costly than inclinometry (€ 26,255), and 2.5-fold more costly than self-reported data (€ 12,491). Simulated scenarios showed altering design strategy could substantially impact processing costs. This was shown for both fixed parameters, such as software development and training costs, and variable parameters, such as the number of work-shift files processed, as well as the sampling frequency for video observation.  When data collection and data processing costs were combined, the cost difference between video and inclinometer methods was reduced to 7%; simulated data showed this difference could be diminished and, even, reversed at larger study sample sizes. Self-report remained substantially less costly under all design strategies, but produced alternate exposure metrics. 

    Conclusions. These findings build on the previously published data collection phase cost model by reporting costs for post-collection data processing of the same data set.  Together, these models permit empirically based study planning and identification of cost-efficient study designs.

  • 20.
    Wahlström, Jens
    et al.
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning. Department of Public Health and Clinical Medicine, Occupational and Environmental Medicine, Umeå University, Umeå, Sweden.
    Bergsten, Eva
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Trask, Catherine
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning. Centre for Health and Safety in Agriculture, College of Medicine, University of Saskatchewan, Saskatoon, SK, Canada.
    Mathiassen, Svend Erik
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Jackson, Jennie
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Forsman, Mikael
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning. IMM Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
    Full-shift trunk and upper arm postures and movements among aircraft baggage handlers2016Inngår i: Annals of Occupational Hygiene, ISSN 0003-4878, E-ISSN 1475-3162, Vol. 60, nr 8, s. 977-990Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Objectives: The present study assessed full shift trunk and upper arm postural exposure amplitudes, frequencies, and durations among Swedish airport baggage handlers, and aimed to determine whether exposures differ between workers at the ramp (loading and unloading aircraft) and baggage sorting areas.

    Methods: Trunk and upper arm postures were measured using inclinometers during three full work shifts on each of 27, male baggage handlers working at a large Swedish airport. Sixteen of the baggage handlers worked on the ramp and 11 in the sorting area. Variables summarizing postures and movements were calculated, and mean values and variance components between subjects and within subject (between days) were estimated using restricted maximum likelihood algorithms in a one-way random effect model.

    Results: In total, data from 79 full shifts (651 hours) were collected with a mean recording time of 495 minutes per shift (range 319-632). On average, baggage handlers worked with the right and left arm elevated >60° for 6.4% and 6.3% of the total workday, respectively. The 90th percentile trunk forward projection (FP) was 34.1° and the 50th percentile trunk movement velocity was 8°s-1. For most trunk (FP) and upper arm exposure variables, between-subject variability was considerable, suggesting that the flight baggage handlers were not a homogeneously exposed group. A notable between-days variability pointed to the contents of the job differing on different days. Peak exposures (>90°) were higher for ramp workers than for sorting area workers (trunk 0.6% ramp vs 0.3% sorting; right arm 1.3% ramp vs 0.7% sorting).

    Conclusions: Trunk and upper arm postures and movements among flight baggage handlers measured by inclinometry were similar to those found in other jobs comprising manual material handling, known to be associated with increased risks for musculoskeletal disorders. The results showed that full-shift trunk (FP), and to some extent peak arm exposures, were higher for ramp workers compared to sorting workers.

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