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Forsman, Mikael
Publications (10 of 20) Show all publications
Domkin, D., Forsman, M. & Richter, H. O. (2019). Effect of ciliary-muscle contraction force on trapezius muscle activity during computer mouse work. European Journal of Applied Physiology, 119(2), 389-397
Open this publication in new window or tab >>Effect of ciliary-muscle contraction force on trapezius muscle activity during computer mouse work
2019 (English)In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 119, no 2, p. 389-397Article in journal (Refereed) Published
Abstract [en]

The present study aimed to identify whether or not an increase in ciliary-muscle contraction force, when the eye-lens is adjusted for viewing at a near distance, result in an increase in trapezius muscle activity, while performing a natural work task. Twelve participants, ranging in age from 21 to 32 years, performed a computer-mouse work task during free gaze conditions. A moving visual target was tracked with a computer mouse on a screen placed at two different distances from the eyes, 25 cm and 50 cm. Tracking performance, eye accommodation, and bilateral trapezius muscle activity were measured continuously. Ciliary-muscle contraction force was computed according to a formula which takes into account the age-dependent, non-linear relationship between contraction force of the ciliary muscle and the produced level of eye accommodation. Generalized Estimating Equations analyses were performed. On the dominant hand side and for the nearest screen distance, there was a significant effect of ciliary-muscle contraction force on the trapezius muscle activity (p<0.001). No other effects were significant (p>0.05). The results support the hypothesis that high visual demands, during computer mouse work, increase ciliary muscle contraction force and contribute to a raise of the sustained level of trapezius muscle activity. The current study specifically clarifies the validity of the relationship between ciliary-muscle contraction force and trapezius muscle activity and demonstrates that this relationship is not due to a general personal trait. We conclude that a high level of ciliary muscle contraction force can contribute to a development of musculoskeletal complaints in the neck-shoulder area.

Keywords
Ciliary-muscle contraction force; Computer mouse work; Electromyography; Eye-accommodation; Trapezius muscle; Visual ergonomics
National Category
Occupational Health and Environmental Health
Identifiers
urn:nbn:se:hig:diva-26194 (URN)10.1007/s00421-018-4031-8 (DOI)000457735500006 ()30430279 (PubMedID)2-s2.0-85056460114 (Scopus ID)
Funder
Forte, Swedish Research Council for Health, Working Life and Welfare, 2009-1761
Available from: 2018-03-01 Created: 2018-03-01 Last updated: 2019-03-12Bibliographically approved
Neumann, W. P., Winkel, J., Palmerud, G. & Forsman, M. (2018). Innovation and employee injury risk in automotive disassembly operations. International Journal of Production Research, 56(9), 3188-3203
Open this publication in new window or tab >>Innovation and employee injury risk in automotive disassembly operations
2018 (English)In: International Journal of Production Research, ISSN 0020-7543, E-ISSN 1366-588X, Vol. 56, no 9, p. 3188-3203Article in journal (Refereed) Published
Abstract [en]

Engineering innovations in car disassembly systems are studied for affects on system operators’ risk of repetitive strain injury (RSI). Objective instrumented measures of injury risk factors with synchronized video-based task analyses were used to examine changes in operators’ RSI risk during two cases of engineering innovation: 1) a shift in industrial model from traditional extracting saleable parts to line-based full material recovery, and 2) the prospective effects of a simulated “Lean” inspired process improvement in the line system.

Both cases of innovation showed significantly increased movement speeds and reduced muscular recovery opportunities, implying increased RSI risk. This case study reveals a mechanism by which innovation may increase RSI risks for operators. Managers responsible for engineering innovation should ensure their teams have the tools and mandate necessary to control injury hazards as part of the development and design process. These cases suggest how failure to manage RSI hazards in the innovation process may allow increases of injury risks that can compromise operational performance. This “innovation pitfall” has implications for operator health and organizational sustainability. Alternative pathways are discussed.

Place, publisher, year, edition, pages
Taylor & Francis, 2018
Keywords
Human Factors, Corporate Social Responsibility, Ergonomics, Disassembly, Design af Production Systems, Workload Control, Closed-loop Supply Chain
National Category
Occupational Health and Environmental Health
Identifiers
urn:nbn:se:hig:diva-26137 (URN)10.1080/00207543.2018.1432910 (DOI)000434401700010 ()2-s2.0-85042937746 (Scopus ID)
Available from: 2018-02-12 Created: 2018-02-12 Last updated: 2018-06-25Bibliographically approved
Zetterberg, C., Richter, H. & Forsman, M. (2015). Temporal co-variation between eye lens accommodation and trapezius muscle activity during a dynamic near-far visual task. PLoS ONE, 10(5), Article ID e0126578.
Open this publication in new window or tab >>Temporal co-variation between eye lens accommodation and trapezius muscle activity during a dynamic near-far visual task
2015 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 10, no 5, article id e0126578Article in journal (Refereed) Published
Abstract [en]

Near work is associated with increased activity in the neck and shoulder muscles, but the underlying mechanism is still unknown. This study was designed to determine whether a dynamic change in focus, alternating between a nearby and a more distant visual target, produces a direct parallel change in trapezius muscle activity. Fourteen healthy controls and 12 patients with a history of visual and neck/shoulder symptoms performed a Near-Far visual task under three different viewing conditions; one neutral condition with no trial lenses, one condition with negative trial lenses to create increased accommodation, and one condition with positive trial lenses to create decreased accommodation. Eye lens accommodation and trapezius muscle activity were continuously recorded. The trapezius muscle activity was significantly higher during Near than during Far focusing periods for both groups within the neutral viewing condition, and there was a significant co-variation in time between accommodation and trapezius muscle activity within the neutral and positive viewing conditions for the control group. In conclusion, these results reveal a connection between Near focusing and increased muscle activity during dynamic changes in focus between a nearby and a far target. A direct link, from the accommodation/vergence system to the trapezius muscles cannot be ruled out, but the connection may also be explained by an increased need for eye-neck (head) stabilization when focusing on a nearby target as compared to a more distant target.

Keywords
Accommodation, Ciliary muscle, Computer work, Electromyography, Eye-neck (head) stabilization, Gaze stabilization, Visual ergonomics
National Category
Occupational Health and Environmental Health
Identifiers
urn:nbn:se:hig:diva-16689 (URN)10.1371/journal.pone.0126578 (DOI)000354542500115 ()25961299 (PubMedID)2-s2.0-84930675377 (Scopus ID)
Funder
Forte, Swedish Research Council for Health, Working Life and Welfare, 2005-0488; 2009-1761
Available from: 2014-05-23 Created: 2014-05-23 Last updated: 2018-03-13Bibliographically approved
Richter, H., Zetterberg, C. & Forsman, M. (2015). Trapezius muscle activity increases during near work activity regardless of accommodation/vergence demand level. European Journal of Applied Physiology, 115(7), 1501-1512
Open this publication in new window or tab >>Trapezius muscle activity increases during near work activity regardless of accommodation/vergence demand level
2015 (English)In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 115, no 7, p. 1501-1512Article in journal (Refereed) Published
Abstract [en]

Aim

To investigate if trapezius muscle activity increases over time during visually demanding near work.

Methods

The vision task consisted of sustained focusing on a contrast-varying black and white Gabor grating. Sixty-six participants with a median age of 38 (range 19–47) fixated the grating from a distance of 65 cm (1.5 D) during four counterbalanced 7-min periods: binocularly through −3.5 D lenses, and monocularly through −3.5 D, 0 D and +3.5 D. Accommodation, heart rate variability and trapezius muscle activity were recorded in parallel.

Results

General estimating equation analyses showed that trapezius muscle activity increased significantly over time in all four lens conditions. A concurrent effect of accommodation response on trapezius muscle activity was observed with the minus lenses irrespective of whether incongruence between accommodation and convergence was present or not.

Conclusions

Trapezius muscle activity increased significantly over time during the near work task. The increase in muscle activity over time may be caused by an increased need of mental effort and visual attention to maintain performance during the visual tasks to counteract mental fatigue.

Keywords
Attention fatigue, Accommodation, Békésy test, Compensatory effort, Contrast threshold tracking, Electromyography, Visual ergonomics
National Category
Occupational Health and Environmental Health
Identifiers
urn:nbn:se:hig:diva-18656 (URN)10.1007/s00421-015-3125-9 (DOI)000355872200011 ()25697148 (PubMedID)2-s2.0-84930575168 (Scopus ID)
Funder
Forte, Swedish Research Council for Health, Working Life and Welfare, 2005-0488; 2009-1761
Available from: 2015-01-01 Created: 2015-01-01 Last updated: 2018-03-13Bibliographically approved
Trask, C., Mathiassen, S. E., Wahlström, J. & Forsman, M. (2014). Cost-efficient assessment of biomechanical exposure in occupational groups, exemplified by posture observation and inclinometry. Scandinavian Journal of Work, Environment and Health, 40(3), 252-265
Open this publication in new window or tab >>Cost-efficient assessment of biomechanical exposure in occupational groups, exemplified by posture observation and inclinometry
2014 (English)In: Scandinavian Journal of Work, Environment and Health, ISSN 0355-3140, E-ISSN 1795-990X, Vol. 40, no 3, p. 252-265Article in journal (Refereed) Published
Abstract [en]

Objectives: This study compared the cost-efficiency of observation and inclinometer assessment of trunk and upper arm inclination in a population of flight baggage handlers, as an illustration of a general procedure for addressing the trade-off between resource consumption and statistical performance in occupational epidemiology.

Methods:  Trunk and upper arm inclination with respect to the line of gravity were assessed for 3 days on each of 27 airport baggage handlers using simultaneous recordings by inclinometers and video.  Labour and equipment costs associated with data collection and data processing were tracked throughout.  Statistical performance, in terms of the inverse of the standard deviation and root mean squared error of the group mean exposure, was computed from the variance components within and between workers, and bias (with inclinometer assumed to produce ‘correct’ inclination angles).  The behavior of the trade-off between cost and efficiency with changed sample size, as well as with changed logistics for data collection and processing, was investigated using simulations.

Results:  At similar total costs, time spent at trunk and arm inclination angles greater than 60 degrees as well as 90th percentile arm inclination were estimated at higher precision using inclinometers, while median inclination and 90th percentile trunk inclination was determined more precisely using observation.  This hierarchy persisted in a scenario where the study was immediately reproduced in another population, while inclinometry was more cost-efficient than observation for all three posture variables in a scenario where data were already collected and only needed to be processed. Observations showed to be biased relative to the –assumed to be correct – inclinometer data, and so inclinometry became the most cost-efficient option for all posture variables and irrespective of scenario when statistical performance was measured by bias and precision combined.

Conclusions: Inclinometers were more cost-efficient in use than observation for two out of three posture metrics investigated when statistical performance was measured only in terms of precision. Since observations were biased, inclinometers consistently outperformed observation when both bias and precision were included in statistical performance. The presented general model for assessing cost-efficiency may be used for designing exposure assessment strategies with considerations not only to statistical criteria, but even to costs. The empirical data provide a specific basis for planning assessments of working postures in occupational groups.

Keywords
Ergonomics, cost-efficiency, posture, shoulder, back, inclinometry, observation, questionnaire, work-related musculoskeletal disorders, baggage handling
National Category
Occupational Health and Environmental Health
Identifiers
urn:nbn:se:hig:diva-14743 (URN)10.5271/sjweh.3416 (DOI)000335288600006 ()2-s2.0-84899829766 (Scopus ID)
Funder
Forte, Swedish Research Council for Health, Working Life and WelfareAFA Insurance
Available from: 2013-06-25 Created: 2013-06-25 Last updated: 2018-03-13Bibliographically approved
Elcadi, G., Forsman, M., Hallman, D., Aasa, U., Fahlström, M. & Crenshaw, A. (2014). Oxygenation and hemodynamics do not underlie early muscle fatigue for patients with work-related muscle pain. PLoS ONE, 9(4), e95582
Open this publication in new window or tab >>Oxygenation and hemodynamics do not underlie early muscle fatigue for patients with work-related muscle pain
Show others...
2014 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, no 4, p. e95582-Article in journal (Refereed) Published
Abstract [en]

Patients suffering from work-related muscle pain (WRMP) fatigue earlier during exercise than healthy controls. Inadequate oxygen consumption and/or inadequate blood supply can influence the ability of the muscles to withstand fatigue. However, it remains unknown if oxygenation and hemodynamics are associated with early fatigue in muscles of WRMP patients. In the present study we applied near-infrared spectroscopy (NIRS) on the extensor carpi radialis (ECR) and trapezius (TD) muscles of patients with WRMP (n = 18) and healthy controls (n = 17). Our objective was to determine if there were group differences in endurance times for a low-level contraction of 15% maximal voluntary contraction (MVC) – sustained for 12-13 min, and to see if these differences were associated with differences in muscle oxygenation and hemodynamics. At baseline, oxygen saturation (StO2%) was similar between groups for the ECR, but StO2% was significantly lower for TD for the WRMP patients (76%) compared to controls (85%) (P < 0.01). Also, baseline ECR blood flow was similar in the two groups. For both muscles there were a larger number of patients, compared to controls, that did not maintain the 15% MVC for the allotted time. Consequently, the endurance times were significantly shorter for the WRMP patients than controls (medians, ECR: 347 s vs. 582 s; TD: 430 s vs. 723 s respectively). Responses in StO2% during the contractions were not significantly different between groups for either muscle, i.e. no apparent difference in oxygen consumption. Overall, we interpret our findings to indicate that the early fatigue for our WRMP patients was not associated with muscle oxygenation and hemodynamics.

Keywords
Near Infrared Spectroscopy, Electromyography, muscle pain, trapezius, extensor carpi radialis, oxygenation, hemodynamics, fatigue
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:hig:diva-16596 (URN)10.1371/journal.pone.0095582 (DOI)000335240300056 ()24755957 (PubMedID)2-s2.0-84899705131 (Scopus ID)
Available from: 2014-04-30 Created: 2014-04-30 Last updated: 2018-03-13Bibliographically approved
Veiersted, K. B., Forsman, M., Hansson, G.-Å. & Mathiassen, S. E. (2013). Assessment of time patterns of activity and rest in full-shift recordings of trapezius muscle activity - effects of the data processing procedure. Journal of Electromyography & Kinesiology, 23(3), 540-547
Open this publication in new window or tab >>Assessment of time patterns of activity and rest in full-shift recordings of trapezius muscle activity - effects of the data processing procedure
2013 (English)In: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 23, no 3, p. 540-547Article in journal (Refereed) Published
Abstract [en]

The purpose of this paper was to compare the effects of different data reduction procedures on the values of variables characterizing the time pattern of trapezius muscle activity during full work shifts. Surface electromyography (EMG) of the right and left upper trapezius muscles were obtained from 40 young subjects in different occupations, mainly electricians, hairdressers and students. The target EMG variables were gap frequency, muscle rest, and the number and duration of episodes with sustained muscle activity (from 0.13 s to 30 min as minimum duration). These variables were derived from the EMG recordings using different Root Mean Square (RMS) windows (from 0.13 to 6.38 s), and discrimination levels between "activity" and "rest" (0.5, 1 and 2 % of maximal EMG). The results give basis for practical suggestions for EMG analyses of full work shifts. For most variables, a discrimination level of 0.5% EMGmax showed to be preferable. The time proportion of muscle rest and sustained muscle activity should, in general, be preferred over the corresponding frequency measures. Sustained muscle activity should be calculated using a RMS window between 1 and 3 s, and preferably be stated in terms of variables describing time proportions of activity. Uninterrupted activity episodes longer than 10 min proved not to be a useful variable due to limited occurrence in many work shifts.

Keywords
electromyography, muscle activity, data processing, exposure, time variation
National Category
Occupational Health and Environmental Health
Identifiers
urn:nbn:se:hig:diva-12523 (URN)10.1016/j.jelekin.2012.12.004 (DOI)000318905600003 ()2-s2.0-84876976445 (Scopus ID)
Available from: 2012-08-02 Created: 2012-08-02 Last updated: 2018-03-13Bibliographically approved
Zetterberg, C., Forsman, M. & Richter, H. (2013). Effects of visually demanding near work on trapezius muscle activity. Journal of Electromyography & Kinesiology, 23(5), 1190-1198
Open this publication in new window or tab >>Effects of visually demanding near work on trapezius muscle activity
2013 (English)In: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 23, no 5, p. 1190-1198Article in journal (Refereed) Published
Abstract [en]

Poor visual ergonomics is associated with visual and neck/shoulder discomfort, but the relation between visual demands and neck/shoulder muscle activity is unclear. The aims of this study were to investigate whether trapezius muscle activity was affected by: (i) eye-lens accommodation; (ii) incongruence between accommodation and convergence; and (iii) presence of neck/shoulder discomfort. Sixty-six participants (33 controls and 33 with neck pain) performed visually demanding near work under four different trial-lens conditions. Results showed that eye-lens accommodation per se did not affect trapezius muscle activity significantly. However, when incongruence between accommodation and convergence was present, a significant positive relationship between eye-lens accommodation and trapezius muscle activity was found. There were no significant group-differences. It was concluded that incongruence between accommodation and convergence is an important factor in the relation between visually demanding near work and trapezius muscle activity. The relatively low demands on accommodation and convergence in the present study imply that visually demanding near work may contribute to increased muscle activity, and over time to the development of near work related neck/shoulder discomfort.

Keywords
Accommodation, Computer work, Electromyography, Gaze stabilization, Visual ergonomics
National Category
Occupational Health and Environmental Health
Identifiers
urn:nbn:se:hig:diva-15261 (URN)10.1016/j.jelekin.2013.06.003 (DOI)000324024800027 ()2-s2.0-84882875082 (Scopus ID)
Available from: 2013-09-16 Created: 2013-09-16 Last updated: 2018-03-13Bibliographically approved
Forsman, M., Neumann, P., Palmerud, G. & Winkel, J. (2013). Mechanical exposures in serial flow assembly - a proactive intervention research approach. Ergonomics
Open this publication in new window or tab >>Mechanical exposures in serial flow assembly - a proactive intervention research approach
2013 (English)In: Ergonomics, ISSN 0014-0139, E-ISSN 1366-5847Article in journal (Refereed) Submitted
Abstract [en]

The EU End of Life Vehicle (ELV) Directive 2000/53/EC has prompted rationalization initiatives to facilitate recycling of material and components from ELVs. In the present study, technical recordings were used to assess operators' mechanical exposures in a new serial flow system for full material recovery in car disassembly as compared with those of a previous study of traditional craft-type-parallel disassembly. Estimated task-specific mechanical exposures served as a base to simulate how further rationalisation may affect ergonomics in car disassembly. The time proportion of ‘direct work’ (deemed value-adding tasks) was about 30% in both systems, i.e. substantially lower than in modern forward factories. Movement velocities were higher in the new serial system, implying a higher risk for musculoskeletal disorders, while mixed results were found in the comparison of postures.

Simulations revealed increased mechanical exposures, illustrated by increased time in high risk conditions, and decreased duration in low-exposure conditions, when indirect tasks and disturbances (deemed non-value-adding) were removed.

This may illustrate the underlying mechanism of how rationalisations to eliminate "waste" can reduce valuable recovery time and increase employee injury risk over time.

Keywords
Industrial ergonomics, Task analysis, Human-Machine Systems, Organisational Ergonomics, Health risks
National Category
Occupational Health and Environmental Health
Identifiers
urn:nbn:se:hig:diva-13831 (URN)
Available from: 2013-02-13 Created: 2013-02-13 Last updated: 2018-03-13Bibliographically approved
Richter, H., Zetterberg, C. & Forsman, M. (2013). Temporal Dependence of Trapezius Muscle Activation during Sustained Eye-Lens Accommodation at Near. Paper presented at HCI 2013. Lecture Notes in Computer Science, 8026(2), 269-275
Open this publication in new window or tab >>Temporal Dependence of Trapezius Muscle Activation during Sustained Eye-Lens Accommodation at Near
2013 (English)In: Lecture Notes in Computer Science, ISSN 0302-9743, E-ISSN 1611-3349, Vol. 8026, no 2, p. 269-275Article in journal (Refereed) Published
Abstract [en]

In this experimental study different levels of oculomotor load were induced via optical trial lenses. The aim was to investigate the temporal dependence of a moderate visual load on trapezius muscle activity. Trapezius muscle activity was measured with bipolar surface electromyography (EMG). Sixty-six subjects with a median age of 36 (range 19–47, std 8) viewed a black and white Gabor grating (5 c/deg) through 0 D, and -3.5 D lenses, in periods of 7-min. An auto refractor was used to continuously sample data on eye-lens accommodation during the vision tasks. Response-diopters were used as a dichotomous high/low accommodation grouping variable. For these groups EMG amplitudes during minutes 1-7 per each lens trial were studied separately with Generalized Estimating Equations (GEE). The analysis results showed significant increases in trapezius muscle activity over time for both viewing conditions. For the binocular -3.5 D condition response-diopters gave a significant positive contribution to the EMG amplitude. The results indicate that sustained eye-lens accommodation at near, during ergonomically unfavorable viewing conditions, may increase the risk for trapezius muscle myalgia.

Place, publisher, year, edition, pages
Springer Publishing Company, 2013
Keywords
Visual ergonomics
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:hig:diva-15182 (URN)10.1007/978-3-642-39182-8_32 (DOI)2-s2.0-84879910212 (Scopus ID)
Conference
HCI 2013
Funder
FAS, Swedish Council for Working Life and Social Research, Dnr 2009-1761
Available from: 2013-09-10 Created: 2013-09-10 Last updated: 2018-03-13Bibliographically approved
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