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  • 1.
    Domkin, Dmitry
    et al.
    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.
    Forsman, Mikael
    Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.; KTH Royal Institute of Technology, Stockholm, Sweden.
    Richter, Hans O.
    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.
    Effect of ciliary-muscle contraction force on trapezius muscle activity during computer mouse work2019In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 119, no 2, p. 389-397Article in journal (Refereed)
    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.

  • 2.
    Elcadi, Guilherme
    et al.
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, CBF. University of Gävle, Centre for Musculoskeletal Research.
    Forsman, Mikael
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, CBF. University of Gävle, Centre for Musculoskeletal Research. Occupational and Environmental Medicine, Public Health Sciences, Stockholm, Sweden.
    Crenshaw, Albert
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, CBF. University of Gävle, Centre for Musculoskeletal Research.
    The relationship between myoelectric activity and oxygenation during isometric contractions in the forearm and shoulder muscles of healthy males and females2010In: The XVIII Congress of the International Society of Electrophysiology and Kinesiology (ISEK), 2010Conference paper (Refereed)
  • 3.
    Elcadi, Guilherme
    et al.
    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. Department of Community Medicine and Rehabilitation, Rehabilitation medicine, Umeå University, Umeå, Sweden.
    Forsman, Mikael
    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. Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
    Hallman, David
    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.
    Aasa, Ulrika
    5 Department of Community Medicine and Rehabilitation, Physiotherapy, Umeå University, Umeå, Sweden.
    Fahlström, Martin
    Department of Community Medicine and Rehabilitation and Department of Clinical Sciences, Umeå University, Umeå, Sweden .
    Crenshaw, Albert
    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.
    Oxygenation and hemodynamics do not underlie early muscle fatigue for patients with work-related muscle pain2014In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, no 4, p. e95582-Article in journal (Refereed)
    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.

  • 4.
    Elcadi, Guilherme H
    et al.
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, CBF. University of Gävle, Centre for Musculoskeletal Research. University of Umeå, Sweden .
    Forsman, Mikael
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, CBF. University of Gävle, Centre for Musculoskeletal Research. Karolinska Institutet, Stockholm, Sweden .
    Crenshaw, Albert G
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, CBF. University of Gävle, Centre for Musculoskeletal Research.
    The relationship between oxygenation and myoelectric activity in the forearm and shoulder muscles of males and females2011In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 111, no 4, p. 647-58Article in journal (Refereed)
    Abstract [en]

    The aim was to investigate the relationship between oxygen saturation (StO(2)%) measured with near-infrared spectroscopy (NIRS) and myoelectric activity (root mean square, RMS) for the extensor carpi radialis (ECR) and trapezius muscles. In addition, gender differences were examined for submaximal (10-70% MVC) and sustained (10% MVC for 5 min) isometric contractions. Thirteen males and 15 females participated. Changes in StO(2)% (∆StO(2)%) and RMS, expressed as percentages of maximum, were calculated for each submaximal contraction. A good correlation between ∆StO(2)% and RMS was seen for the ECR (r = -0.53) and a moderate correlation seen for the trapezius muscle (r = -0.44). The ANOVA showed a significant decrease in ECR-∆StO(2)% over force with females demonstrating a tendency for larger changes than males. ECR-RMS increased over force with no impact of gender. For the trapezius, ∆StO(2)% decreased over force but was not gender dependent. Trapezius-RMS increased over force with females demonstrating a tendency for greater change than males. For the sustained contraction, ECR-StO(2)% changed over time but was not gender dependent. ECR-RMS increased over time with females showing a greater response than males. Trapezius-StO(2)% changed over time and differed between genders, i.e., males increased while females decreased. RMS increased over time similarly for both genders. In conclusion, our data show that the ECR and trapezius aerobic demands during isometric contractions are negatively correlated to electromyography (EMG) RMS. The present study also suggests some gender specificity for forearm and shoulder myoelectric activity and oxygenation for submaximal and sustained contractions.

  • 5.
    Forsman, Mikael
    et al.
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, CBF. University of Gävle, Centre for Musculoskeletal Research.
    Bernmark, Eva
    Department of Public Health Sciences, Division of Occupational and Environmental Medicine, Karolinska Institutet.
    Nilsson, Birgitta
    Innventia AB.
    Pousette, Sandra
    Innventia AB.
    Mathiassen, Svend Erik
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, CBF. University of Gävle, Centre for Musculoskeletal Research.
    Participative development of packages in the food industry – evaluation of ergonomics and productivity by objective measurements2012In: Work: A journal of Prevention, Assesment and rehabilitation, ISSN 1051-9815, E-ISSN 1875-9270, Vol. 41, p. 1751-1755Article in journal (Refereed)
    Abstract [en]

    Rationalizations generally have a negative effect on health and known risk factors for musculoskeletal disorders. These effects may be reduced by paying attention to modifiers as worker participation and a resonant management style. In this study a participatory approach was used in the food industry in order to improve ergonomics and productivity. The food industry shows a high prevalence of musculoskeletal disorders, and repetitive manual work occurs extensively. Prototypes of new packaging solutions were developed in three cases, and compared in a simulated production to the existing production system through direct measurements of working postures and muscle activity, ratings of physical load, and general productivity data. Measured and rated ergonomic exposures showed that workload was significantly lower for the prototypes, in all three cases. In two cases, the number of handling operations included in the packaging operations were greatly reduced with the prototype package, as were production costs. The impact on disorders of the obtained load reductions is difficult to assess, but we believe that in “critical” situations like this, even small improvements may have an effect. This study shows that workloads during manual handling of packages as well as production costs can be reduced by applying participative development of packages.

  • 6.
    Forsman, Mikael
    et al.
    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.
    Neumann, Patrick
    Ryerson University, Mechanical Engineering, Toronto.
    Palmerud, Gunnar
    Arbets- och miljömedicin, Göteborgs universitet.
    Winkel, Jörgen
    Institutionen för sociologi och arbetsvetenskap, Göteborgs universitet.
    Mechanical exposures in serial flow assembly - a proactive intervention research approach2013In: Ergonomics, ISSN 0014-0139, E-ISSN 1366-5847Article in journal (Refereed)
    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.

  • 7.
    Forsman, Mikael
    et al.
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, CBF. University of Gävle, Centre for Musculoskeletal Research.
    Neumann, Patrick
    Department of Mechanical and Industrial Engineering, Ryerson University, Toronto.
    Palmerud, Gunnar
    Occupational and Environmental Medicine, University of Gothenburg.
    Winkel, Jörgen
    Department of Sociology and Work Science, University of Gothenburg.
    Simulating the effects of efficiency improvement efforts in car disassembly2012Conference paper (Refereed)
  • 8.
    Lodin, Camilla
    et al.
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, CBF. University of Gävle, Centre for Musculoskeletal Research.
    Forsman, Mikael
    Karolinska Institutet.
    Richter, Hans
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, CBF. University of Gävle, Centre for Musculoskeletal Research.
    Sustained periods of binocular load may affect trapezius muscle activity2011In: Wellbeing and innovations through ergonomics: Proceedings of NES2011 / [ed] Juha Lindfors, Merja Savolainen, Seppo Väyrynen, Oulu, Finland: Nordic Ergonomics Society , 2011, p. 158-163Conference paper (Refereed)
    Abstract [en]

    The relationship between activity in ocular muscles and activity in neck and scapular muscles that stabilizes gaze is well known. However, it is uncertain if ocular load per se contributes to increased muscle activity in the neck and scapular area. Sixty-six participants performed a fixation task under three different conditions: binocular with minus lenses (-3.5D) and monocular with minus lens (-3.5D) and neutral lens (±0D). Ocular accommodation and trapezius muscle EMG were measured. Multiple regression analysis showed that response diopters accounted for 11.6% (p=0.009) of the variance in EMG in the binocular condition. In the monocular conditions, there were no significant relationships.

  • 9.
    Mathiassen, Svend Erik
    et al.
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, CBF. University of Gävle, Centre for Musculoskeletal Research.
    Wahlström, Jens
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, CBF. University of Gävle, Centre for Musculoskeletal Research.
    Forsman, Mikael
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, CBF. University of Gävle, Centre for Musculoskeletal Research.
    Bias and imprecision in posture percentile variables estimated from short exposure samples2012In: BMC Medical Research Methodology, ISSN 1471-2288, E-ISSN 1471-2288, Vol. 12, p. 36-Article in journal (Refereed)
    Abstract [en]

    Background. Upper arm postures are believed to be an important risk determinant for musculoskeletal disorder development in the neck and shoulders. The 10th and 90th percentiles of the angular elevation distribution have been reported in many studies as measures of neutral and extreme postural exposures, and variation has been quantified by the 10th-90th percentile range. Further, the 50th percentile is commonly reported as a measure of "average" exposure. These four variables have been estimated using samples of observed or directly measured postures, typically using sampling durations between 5 and 120 min.

    Methods. The present study examined the statistical properties of estimated full-shift values of the 10th, 50th and 90th percentile and the 10th-90th percentile range of right upper arm elevation obtained from samples of seven different durations, ranging from 5 to 240 min. The sampling strategies were realized by simulation, using a parent data set of 73 full-shift, continuous inclinometer recordings among hairdressers. For each shift, sampling duration and exposure variable, the mean, standard deviation and sample dispersion limits (2.5% and 97.5%) of all possible sample estimates obtained at one minute intervals were calculated and compared to the true full-shift exposure value.

    Results. Estimates of the 10th percentile proved to be upward biased with limited sampling, and those of the 90th percentile and the percentile range, downward biased. The 50th percentile was also slightly upwards biased. For all variables, bias was more severe with shorter sampling durations, and it correlated significantly with the true full-shift value for the 10th and 90th percentiles and the percentile range. As expected, shorter samples led to decreased precision of the estimate; sample standard deviations correlated strongly with true full-shift exposure values.

    Conclusions. The documented risk of pronounced bias and low precision of percentile estimates obtained from short posture samples presents a concern in ergonomics research and practice, and suggests that alternative, unbiased exposure variables should be considered if data collection resources are restricted.

  • 10.
    Neumann, W. Patrick
    et al.
    Department of Mechanical and Industrial Engineering, Ryerson University, Toronto, Canada.
    Winkel, Jörgen
    Department of Sociology and Work Science, University of Gothenburg, Gothenburg, Sweden; Department of Management Engineering, Technical University of Denmark, Kongens Lyngby, Denmark.
    Palmerud, Gunnar
    Occupational and Environmental Medicine, University of Gothenburg, Gothenburg, Sweden.
    Forsman, Mikael
    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. Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
    Innovation and employee injury risk in automotive disassembly operations2018In: International Journal of Production Research, ISSN 0020-7543, E-ISSN 1366-588X, Vol. 56, no 9, p. 3188-3203Article in journal (Refereed)
    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.

  • 11.
    Nilsson, Birgitta
    et al.
    Innventia AB.
    Pousette, Sandra
    Innventia AB.
    Forsman, Mikael
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, CBF. University of Gävle, Centre for Musculoskeletal Research.
    Bernmark, Eva
    Department of Public Health Sciences, Karolinska Institutet.
    Mathiassen, Svend Erik
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, CBF. University of Gävle, Centre for Musculoskeletal Research.
    Can producers of packaging contribute to improving the handling of packages for women working in the food industry?2011In: 25th IAPRI Symposium, 2011Conference paper (Refereed)
    Abstract [en]

    Extensive manual handling is a risk factor for work-related musculoskeletal disorders in the lower back and neck-shoulder regions (World Health Organization 2003). In the Swedish food industry, manual handling occurs mainly in production and in packing. The type and structure of packages is a probable determinant of the working conditions. In this research and development project, we investigated whether packages can be redesigned so that workloads during manual handling are reduced.

    The project included the following steps, implemented at three selected production lines different food industry companies:

    - Collection of production data and a description of all manual activities devoted to the handling of packages.

    - Direct measurements of working postures and muscle activity of the upper body, together with ratings of physical load using questionnaires.

    - Collection of general productivity data.

    - Group discussions with workers concerning the packaging characteristics supporting or obstructing easy handling; followed by suggestions for improvements.

    - Interviewing the next step in the value chain, e.g. bakers and shop replenishers, regarding suggestions for improvements to the selected packages.

    - Discussions with packaging producers regarding improvements to the selected packages.

    - Feed-back of results to the participating companies.

    The existing production systems and the manual handling activities observed there were compared to simulated production using prototypes of new packages. Measured and rated ergonomic exposures showed that workload was lower for the prototypes. In one company (N=9), muscular activity decreased by 10.1%  (p<0.05). In the second company (N=4) postures were less inclined during work, and  muscular activity declined by 43.6% . In the third company (N=8), wrist velocity decreased by 7% (p<0.05). In the two latter companies, the number of handling operations included in the packaging operations was greatly reduced with the prototype package. None of the new prototype solutions had negative effects on productivity.

    From these cases, we conclude that workloads during manual handling of packages can be reduced by modifying packages per se. We believe that considerations to the ergonomics effects of a particular package should be included in the planning, design and specifications of that package throughout its value chain.

  • 12.
    Palmerud, Gunnar
    et al.
    Occupational and Environmental Medicine, University of Gothenburg, Sweden.
    Forsman, Mikael
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, CBF. University of Gävle, Centre for Musculoskeletal Research.
    Neumann, Patrick
    Department of Mechanical and Industrial Engineering, Ryerson University, Toronto, Canada.
    Winkel, Jörgen
    Department of Sociology and Work Science, University of Gothenburg, Sweden.
    Mechanical exposure implications of rationalization: A comparison of two flow strategies in a Swedish manufacturing plant2012In: Applied Ergonomics, ISSN 0003-6870, E-ISSN 1872-9126, Vol. 43, no 6, p. 1110-1121Article in journal (Refereed)
    Abstract [en]

    The aim of this case study was to (1) investigate differences in mechanical exposure (i.e. mechanical forces arising in the body of the operator) between two production strategies: long-cycle parallelised flow assembly (OLD) and conventional serial flow assembly (NEW), and (2) estimate potential changes in job exposure as a consequence of waste reduction when rationalising a line system.

    Data on postures, movements and whole body exposure were collected during an ordinary working shift, by means of video recordings synchronised to direct technical measurements of six professional operators.

    The results revealed the machine paced NEW system to have slower movements with less time spent in movements of high velocity compared to the self-paced OLD system. No significant differences were found between time-median posture levels. ‘Disturbances’ in the NEW system offered lower mechanical risk exposures compared to direct assembly work. Modelling the removal of wasteful ‘disturbances’ revealed both an increase in risk-implying fast movements and decrease in recovery-implying periods at low velocity – effectively isolating a work intensification. This study helps expose the complex relationship between rationalizations and mechanical exposure for system operators

  • 13.
    Richter, Hans
    et al.
    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.
    Zetterberg, Camilla
    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.
    Forsman, Mikael
    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. Karolinska Institut, Stockholm, Sweden .
    Temporal Dependence of Trapezius Muscle Activation during Sustained Eye-Lens Accommodation at Near2013In: Lecture Notes in Computer Science, ISSN 0302-9743, E-ISSN 1611-3349, Vol. 8026, no 2, p. 269-275Article in journal (Refereed)
    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.

  • 14.
    Richter, Hans
    et al.
    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.
    Zetterberg, Camilla
    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. Section of Occupational and Environmental Medicine, Department of Medical Sciences, Uppsala University, Uppsala, Sweden.
    Forsman, Mikael
    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. Division of Occupational and Environmental Medicine, Department of Public Health Sciences, Karolinska Institutet, Stockholm, Sweden.
    Trapezius muscle activity increases during near work activity regardless of accommodation/vergence demand level2015In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 115, no 7, p. 1501-1512Article in journal (Refereed)
    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.

  • 15.
    Toomingas, Allan
    et al.
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, CBF. University of Gävle, Centre for Musculoskeletal Research.
    Forsman, Mikael
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, CBF. University of Gävle, Centre for Musculoskeletal Research.
    Mathiassen, Svend Erik
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, CBF. University of Gävle, Centre for Musculoskeletal Research.
    Heiden, Marina
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, CBF. University of Gävle, Centre for Musculoskeletal Research.
    Nilsson, Tohr
    Department of Public Health and Clinical Medicine, Umeå university.
    Variation between seated and standing/walking postures among male and female call centre operators2012In: BMC Public Health, ISSN 1471-2458, E-ISSN 1471-2458, Vol. 12, p. 154-Article in journal (Refereed)
    Abstract [en]

    Purpose: The aim of the present study was to assess variation in gross body posture amongst male and female call centre operators using whole-day registrations of seated and standing/walking periods, analyzed and described by a number of novel variables.

    Methods: Body postures, identified as either seated or standing/walking, were recorded using inclinometers throughout an entire work shift for 43 male and 97 female call centre operators at 16 call centres. Data were analyzed using an extensive set of variables describing occurrence of postures, switches between postures, posture similarities across the day, and compliance with posture recommendations.

    Results: The majority of the operators, both male and female, spent more than 80% of the shift in a seated posture. The average number of switches between seated and standing/walking or vice versa was 10.4 per hour. Female operators spent, on average, 11% of the day in periods of sustained sitting longer than 1 hour; male operators only 4.6% of the day (p=0.013). Only 38% of the operators followed current standard recommendations of having an uninterrupted break from seated work, lasting a minimum of 5minutes within a one hour of work and only 11% of operators had a 10 minute (or longer) uninterrupted break. Substantial variation between operators was observed in many variables. Since work tasks were essentially similar across operators and were expected to be similar across days, this indicates individual differences in working technique.

    Conclusions: The dominance of seated work for extended periods indicates that efforts should be made at call centres to introduce more gross physical variation during the work day. Appropriate and effective initiatives for realizing this intervention need to be identified

  • 16.
    Trask, Catherine
    et al.
    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.
    Mathiassen, Svend Erik
    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.
    Wahlström, Jens
    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.
    Forsman, Mikael
    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.
    Cost-efficient assessment of biomechanical exposure in occupational groups, exemplified by posture observation and inclinometry2014In: Scandinavian Journal of Work, Environment and Health, ISSN 0355-3140, E-ISSN 1795-990X, Vol. 40, no 3, p. 252-265Article in journal (Refereed)
    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.

  • 17.
    Veiersted, Kaj Bo
    et al.
    National Institute of Occupational Health, Oslo.
    Forsman, Mikael
    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.
    Hansson, Gert-Åke
    Division of Occupational and Environmental Medicine, Lund University.
    Mathiassen, Svend Erik
    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.
    Assessment of time patterns of activity and rest in full-shift recordings of trapezius muscle activity - effects of the data processing procedure2013In: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 23, no 3, p. 540-547Article in journal (Refereed)
    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.

  • 18.
    Veiersted, KB
    et al.
    National Institute of Occupational Health, Oslo, Norway.
    Forsman, Mikael
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, CBF. University of Gävle, Centre for Musculoskeletal Research.
    Mathiassen, Svend Erik
    University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, CBF. University of Gävle, Centre for Musculoskeletal Research.
    Sulma-periods or bursts: which risk estimating parameters should be used in analyses of long time EMG recordings2010In: The XVIII Congress of the International Society of Electrophysiology and Kinesiology (ISEK), Aalborg, Denmark, 2010Conference paper (Refereed)
    Abstract [en]

    AIM: Sustained trapezius muscle activity has been shown to increase the risk of neck and shoulder pain: number of eight-minute-periods with sustained low-level muscle activity >0.5% EMGmax (SULMA-periods, (1)), and more than 70% of burst time, i.e. working time above 2% EMGmax (2). Both studies consider the occurrence of continuous muscle activity above a certain discrimination level. The aim of this study was to evaluate the effect of data processing procedures on similar measures of sustained trapezius muscle activity.

    METHODS: Full-day bilateral EMG from upper trapezius muscles were collected from forty subjects (17 men, 23 women, median age 22 years, range 22-26), who had just left technical school and started mainly as hairdressers, electricians and students. Number of periods and total duration of activity above discrimination levels 0.5, 1 and 2% EMGmax were retrieved from data processed by each of six Root Mean Square (RMS) window lengths. Several analyses of patterns of activity and rest were made, and this paper presents some basic descriptives concerning total duration of muscle activity.

    RESULTS: The static muscle activity level (APDF) was 0.3% EMGmax and the mean burst time was 65%. The total time of muscle activity depended largely on the discrimination level (Figure: panel A compared to B). For all discrimination levels, the total activity time increased with an increasing RMS length, and became larger when the demands for a minimum period duration were relaxed (figures A and B).

    CONCLUSION: Thus, muscle activity patterns extracted from EMG are highly sensitive to the data processing procedure and we suggest that a standardized approach should be developed so that future studies will be comparable.

  • 19.
    Zetterberg, Camilla
    et al.
    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.
    Forsman, Mikael
    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. Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
    Richter, Hans
    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.
    Effects of visually demanding near work on trapezius muscle activity2013In: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 23, no 5, p. 1190-1198Article in journal (Refereed)
    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.

  • 20.
    Zetterberg, Camilla
    et al.
    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. Department of Medical Sciences, Section of Occupational and Environmental Medicine, Uppsala University, Uppsala, Sweden..
    Richter, Hans
    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.
    Forsman, Mikael
    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. Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
    Temporal co-variation between eye lens accommodation and trapezius muscle activity during a dynamic near-far visual task2015In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 10, no 5, article id e0126578Article in journal (Refereed)
    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.

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