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Bias and Precision in Biomechanical Exposure Assessment: Making the Most of our Methods
University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, Occupational health science. University of Gävle, Centre for Musculoskeletal Research. Uppsala universitet.ORCID iD: 0000-0003-2939-0236
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
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.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. , p. 90
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 1329
Keywords [en]
measurement strategy, accuracy, inclinometry, electromyography, EMG, upper arm, shoulder, low back, lumbar, thoracic
National Category
Occupational Health and Environmental Health
Research subject
Health-Promoting Work
Identifiers
URN: urn:nbn:se:hig:diva-23952ISBN: 978-91-554-9902-0 (print)OAI: oai:DiVA.org:hig-23952DiVA, id: diva2:1092199
Public defence
2017-06-02, Krusenstjernasalen, Biblioteket, Kungsbäcksvägen 47, Gävle, 13:00 (English)
Opponent
Supervisors
Funder
Forte, Swedish Research Council for Health, Working Life and Welfare, 2009-1761Available from: 2017-05-23 Created: 2017-05-02 Last updated: 2024-01-26Bibliographically approved
List of papers
1. Is what you see what you get? Standard inclinometry of set upper arm elevation angles
Open this publication in new window or tab >>Is what you see what you get? Standard inclinometry of set upper arm elevation angles
Show others...
2015 (English)In: Applied Ergonomics, ISSN 0003-6870, E-ISSN 1872-9126, Vol. 47, p. 242-252Article in journal (Refereed) Published
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.

Keywords
measurement error, observation, working postures
National Category
Occupational Health and Environmental Health
Identifiers
urn:nbn:se:hig:diva-16159 (URN)10.1016/j.apergo.2014.08.014 (DOI)000347663600028 ()25479994 (PubMedID)2-s2.0-84919663729 (Scopus ID)
Available from: 2014-01-24 Created: 2014-01-24 Last updated: 2022-10-25Bibliographically approved
2. Observer performance in estimating upper arm elevation angles under ideal viewing conditions when assisted by posture matching software
Open this publication in new window or tab >>Observer performance in estimating upper arm elevation angles under ideal viewing conditions when assisted by posture matching software
2016 (English)In: Applied Ergonomics, ISSN 0003-6870, E-ISSN 1872-9126, Vol. 55, p. 208-215Article in journal (Refereed) Published
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.

Keywords
measurement error, working postures, observation
National Category
Occupational Health and Environmental Health
Identifiers
urn:nbn:se:hig:diva-19420 (URN)10.1016/j.apergo.2016.01.012 (DOI)000374074600021 ()26995050 (PubMedID)2-s2.0-84959471678 (Scopus ID)
Funder
Forte, Swedish Research Council for Health, Working Life and Welfare, 2009-1761
Available from: 2015-06-01 Created: 2015-06-01 Last updated: 2024-01-26Bibliographically approved
3. Methodological variance associated with normalization of occupational upper trapezius EMG using submaximal reference contractions
Open this publication in new window or tab >>Methodological variance associated with normalization of occupational upper trapezius EMG using submaximal reference contractions
2009 (English)In: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 19, no 3, p. 416-427Article in journal (Refereed) Published
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.

Keywords
Exposure Variability, Variance Components, Assembly work, Trapezius, EMG
National Category
Occupational Health and Environmental Health
Identifiers
urn:nbn:se:hig:diva-1958 (URN)10.1016/j.jelekin.2007.11.004 (DOI)000265508900007 ()18155593 (PubMedID)2-s2.0-62649167005 (Scopus ID)
Available from: 2008-06-11 Created: 2008-06-11 Last updated: 2024-01-26Bibliographically approved
4. Precision based guidelines for sub-maximal normalisation task selection for trunk extensor EMG
Open this publication in new window or tab >>Precision based guidelines for sub-maximal normalisation task selection for trunk extensor EMG
2017 (English)In: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 37, p. 41-51Article in journal (Refereed) Published
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.

Keywords
Exposure variability, variance components, low back, lumbar, erector spinae
National Category
Occupational Health and Environmental Health
Research subject
Health-Promoting Work
Identifiers
urn:nbn:se:hig:diva-23351 (URN)10.1016/j.jelekin.2017.07.001 (DOI)000415646600007 ()28918109 (PubMedID)2-s2.0-85029353680 (Scopus ID)
Funder
Forte, Swedish Research Council for Health, Working Life and Welfare, 2009-1761
Available from: 2017-01-20 Created: 2017-01-20 Last updated: 2024-01-26Bibliographically approved

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