| 1. |
- Elcadi, Guilherme H.
(författare)
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Near infrared spectroscopy for assessing oxygenation and hemodynamics in the upper extremities of healthy subjects and patients with work-related muscle pain
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The prevalence of work-related muscle pain (WRMP) is large in the general population in the industrialized world. Despite significant advances over recent years in some research areas, the mechanisms of why WRMP occurs and the pathophysiological mechanisms behind the disorders are still unclear. One suggested explanation is that WRMP is caused initially by a limitation of the local muscle circulation and oxidative metabolism. There is a lack of objective methods to gauge the development and diagnosis of WRMP. Near infrared spectroscopy (NIRS) is a non-invasive technique that allows for determinations of oxygenation and blood flow. The purpose of this thesis was to evaluate NIRS (1) as a method for measuring muscle oxygenation and hemodynamics for the extensor carpi radialis (ECR) and trapezius descendens muscles (TD), and (2) to investigate whether variables measured by NIRS differed between patients diagnosed with WRMP and healthy subjects. Several variables of NIRS were produced and investigated. These included muscle oxygenation (StO2%), changes during contractions (∆StO2%) and StO2% recovery (Rslope), total hemoglobin (HbT) as an indication of blood volume and its changes during contractions (∆HbT). In addition, for the ECR, by applying an upper arm venous occlusion (VO) HbTslope increase as a surrogate of blood flow, and for both VO and arterial occlusion (AO) HHbslope increase (i.e. deoxyhemoglobin slope) as a surrogate of oxygen consumption were variables of interest. A first objective was to determine how StO2% and HbT responded to various contraction forces and how it related to muscle activation measured by electromyography (EMG). For both muscles isometric contractions of 10, 30, 50 and 70% of maximal voluntary contraction (MVC) were maintained for 20 s each by healthy males and females; additionally a 10% MVC contraction was sustained for 5 min. For the different contraction levels, predictable relationships were seen between ∆StO2% and force, and between ∆StO2% and EMG RMS amplitude. The general trend was a decrease in ∆StO2% with increasing force and increasing EMG. Females showed a tendency for a higher oxygen use (i.e., drop in StO2%) for the ECR over force levels than males and a higher RMS% MVC for the TD. For the 10% MVC contraction sustained for 5 min gender specific changes over time for HbT and RMS for the ECR, and for StO2% for the TD muscle were seen. A second objective was to determine the day-to-day reliability of NIRS variables for the ECR and TD muscles at group level (Pooled data) and at gender level (males and females). Measurements were performed on two occasions separated by 4-6 days and intraclass correlation coefficients (ICC) and limits of agreement (LOA) were determined as reliability and reproducibility indicators, respectively. Variables tested were ∆StO2% during submaximal isometric contractions of 10, 30, 50 and 70% MVC and StO2% recovery (Rslope) after contractions and after AO. For the ECR, HbTslope as an indication of blood flow (using VO) and HHbslope as a surrogate of oxygen consumption for both VO and AO were computed. For ∆StO2% for the ECR the highest ICC was at 30% MVC for both the pooled data and at gender level. For the TD ICCs were comparably high for 30, 50, 70 % MVC (for both muscles the ∆StO2% at 10% MVC showed the lowest ICC). Further, females showed a higher ICC than males for contraction levels of 50 and 70% MVC. For both muscles, LOA for ∆StO2% was lowest at 10% and highest at 50 and 70% MVC. For the ECR Rslope ICCs were high for all contraction levels, but was lower for AO; LOA was lowest at 70% MVC. For the TD, Rslope ICCs were also high for all contraction levels and LOA was lowest at 30 % MVC. ICC for HbTslope was the lowest of all variables tested. For HHbslope ICC was higher for AO than for VO, and LOA was lower for AO. A third objective was to determine if there were differences between healthy subjects and patients diagnosed with WRMP in ∆StO2% and ∆HbT responses during varying submaximal contractions (10, 30, 50 and 70% MVC), and StO2% recovery (Rslope) immediately after contractions and AO. Additional variables tested in the ECR at rest were HHbslope to indicate oxygen consumption (using AO) and HbTslope as an indication of blood flow. There were no differences between groups in ∆StO2% and ∆HbT variables during the contractions or Rslope in the recovery after contractions or AO. Furthermore, HbTslope was not different between groups However, oxygen consumption for the ECR and StO2% for the TD at rest were significantly greater for healthy subjects compared to patients. A fourth objective was to determine if there were differences in StO2% and HbT between healthy subjects and WRMP patients during a 12 min sustained contraction of 15 % MVC. In addition, the protocol included a recovery period of 30 min. Prior to contraction, as well as during the recovery period, HbTslope as a surrogate of blood flow was determined for the ECR. Neither the ECR nor the TD exhibited significant differences between groups for StO2% and HbT during the contraction. For the TD patients showed a lower StO2% value at rest and throughout the contraction than healthy subjects. For the ECR HbT during the sustained contraction the general trend was an initial decrease with gradual increase throughout the contraction for both groups. For HbTslope no differences were seen between patients and healthy subjects before the sustained contraction and during the recovery period for both muscles.NIRS is deemed a suitable technique for assessing physiological measurements of the upper extremity, including for day-to-day testing.NIRS was not able to distinguish between the patients with WRMP and controls. A concern in the thesis is the characteristics of the patient group in being equally active in recreational sports, actively working, and similar in muscle strength as controls. Thus, applying NIRS for studying a more severe patient group could yield different results.
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| 2. |
- Eliasson, Kristina, 1979-
(författare)
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Ergonomists’ risk assessments : From guesstimates to strategic approaches
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Musculoskeletal disorders are among the most prevalent causes of work-related ill-health, consequently risk assessments of hazardous factors related to these disorders are important for prevention. Occupational Health Services (OHS) providers are independent experts, supporting employers regarding work environment issues and rehabilitation. Ergonomists represents one of the professions within OHS, and risk assessment regarding musculoskeletal disorders is within the scope of their work tasks. The overall objective was to explore Swedish ergonomists’ practices and approaches with risk assessments, in order to contribute new knowledge about how ergonomists’ work methods can be further developed to improve prevention of work-related musculoskeletal disorders. Paper I explored the process of risk assessment assignments and the ergonomists’ use of observation-based risk-assessment tools. The result showed a lack of systematic approaches regarding risk assessment assignments and limited use and knowledge of observation-based risk-assessment tools. In Paper II inter-observer and intra-observer reliability of risk assessments, without the use of an explicit observational method were assessed. The results showed a non-acceptable reliability. Paper III explored ergonomists experiences of an e-learning concept for knowledge translation in the OHS context. The e-learning concept was considered as feasible. The knowledge translation inspired increased use of risk-assessment tools, changes in the risk assessment procedures, e.g. selection of tools, and employing a participatory approach. Paper IV described the development of a process model for occupational health surveillance for workers exposed to hand-intensive work (HIW-model), and the studies that will explore the model. Paper V explored company representatives’ experiences of the HIW-model, and factors which facilitated the execution of the model. The model contributed to increased risk awareness and understanding of how individual workers’ musculoskeletal ill-health relates to exposures in work. Facilitating factors were: a joint start-up meeting in which the process was planned, clear communication, and clarity regarding the ownership of the process. In conclusion, the findings showed that ergonomists’ expertise is needed in the entire risk management process and not only in the risk assessment phase. In this process, the ergonomists need to be active and take the expert role (which includes a stocked toolbox) and support the employer through the whole risk management process from initiation to evaluation of risk controlling measures.
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| 3. |
- Forsman, Mikael, 1963
(författare)
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Applications of Magnetic Tracers in the Human Lung and Gastrointestinal Tract
- 1995
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The use of ferrimagnetic material as a tracer represents a noninvasive approach in physiological measurements. Concerning the lung, magnetopneumography, MPG, is a unique technique to estimate retained dust in the lung, using the magnetizable dust fraction as a tracer. First a strong constant magnetic field is briefly applied to the thorax. After the field has been removed, the weak remanent field of the magnetized particles is measured outside the body. The sampled data include information not only about the amount and distribution, but also about the random rotation, of the tracer- particles. In the present work, the MPG method was used in vivo, and developed through model studies toward improved accuracy. Furthermore, applications of the MPG principle (and instrument) in the field of gastrointestinal motility were developed and evaluated. Such applications may constitute future alternatives to clinically established radiological methods, especially for subjects for whom radiation is of particular concern. Previous investigations have shown large inter-individual variations of lung dust retention among arc welders with similar fume exposure history. Here, repeated MPG measurements were used to monitor the retention build-up in a group of eight, previously unexposed, trainees during a welding course. Already after 30 days of exposure there were inter-individual differences in estimated retention of more than a factor of two. A first-order retention model was suggested, including estimated individual dust exposure profiles. The inverse problem of finding the amount and distribution of the source of a measured magnetic field has no unique solution. Anatomical differences of lung and chest shapes are important sources of error when total amounts of lung dust are estimated and inter-individual variations are studied. Multipole analysis involves estimation of a number of coefficients in a truncated sum; one of these represents the total dipole moment, which is proportional to the total amount of dust. In comparison, the commonly used mean value method showed much larger bias error than the multipole methods. Multipole orders up to and including octupoles were needed to describe the field from a magnetized thorax. This model is well suited when measuring total dust load in subjects where dust translocation is of concern, e.g. in studies of human lung dust clearance. Gastric emptying measurements were carried out magnetically on 16 healthy male volunteers. The early part of the mean emptying curve decreased slightly faster than the curve of a corresponding previous scintigraphic study. Rotations (due to intraluminal movements) were studied by measuring the field decay outside the abdomen after magnetization. After a low activity phase of almost linear flux density decay, the mean rotation gradually increased, and the decay became bi-exponential. Moreover, by measuring field maps repeatedly after ingestion, the transit of a swallowed small permanent magnet was followed through the gut. It is concluded that measurements of magnetic fields from ferrimagnetic tracers prove a valuable and promising tool in estimations of retained dust in the lungs, as well as in studies of gastric motility.
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| 4. |
- Jackson, Jennie
(författare)
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Bias and Precision in Biomechanical Exposure Assessment : Making the Most of our Methods
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 5. |
- Mazaheri, Ava, 1992-
(författare)
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Beyond the Force: Redefining load exposure assessments of nutrunners for improved power tool ergonomics
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Reaction force exposure from handheld tightening tools (also known as nutrunners) constitutes an acknowledged contributor to musculoskeletal disorders among assembly operators, and are today not regulated by explicit limits. The research presented in this thesis aimed at contributing to the development of recommended exposure limits for, and assessments of, reaction loads from handheld right-angle and pistol-grip tightening tools.In order to address the thesis objectives, four research studies were conducted. A literature review was conducted to provide an overview of the current state of knowledge within the topic area. Knowledge gaps were identified by mapping available publications and based on those suggesting directions for further research. Thereafter, two psychophysically based experimental studies were conducted where acceptability limits related to load exposure from handheld tightening tools were derived for right-angle and pistol-grip tightening tools. Finally, an automotive manufacturer’s approach to evaluating and managing the use of handheld tightening tools was outlined by means of an interview study.As found through the literature review, four of the forty included publications had stated exposure limits (general recommendations) or acceptability limits (load acceptance as assessed by study participants) for reaction load exposure from handheld tightening tools. However, some of the reported limits did not consider relevant physical parameters, and some did not comply with modern power tool technologies. Based on this, it was suggested that researchers should emphasize physical quantities relevant to the reaction load such as impulse, express exposure limits in terms of reaction load relevant parameters (and not only the tightening torque), and further study modern power tool technologies.The experimental studies resulted in acceptability limits for right-angle and pistol-grip tightening tools expressed as screw-joint tightening torque (i.e. a task-related factor), where acceptable tightening torque limits were higher for the inertia-controlled tightening program compared to the continuous drive tightening program, in both studies. In addition, corresponding acceptable reaction load levels (i.e. the exposure) were derived, indicating load levels resulting from the tool use that the study participants assessed as acceptable for an 8-hour workday. It should be noted that the experimental times on which the acceptability limits are based were limited, and that the acceptability limits therefore should not be prescribed to full workdays.From the interview study, three main topic categories were identified based on the interviewees’ responses: ‘A holistic approach’, ‘Information and knowledge availability’ and ‘Negotiating criteria’. Within the studied automotive organization, a comprehensive approach to ergonomics assessments is incorporate, where both objective and subjective evaluations form the basis for addressing physically demanding tool use situations. Further, it was found that there are different instances where the employees lack sufficient knowledge related to the tools, and which can influence the employment of handheld tightening tools. In addition, it was found that criteria such as safety and quality could in some situations compete with ergonomics efforts. In conclusion, the findings from this thesis can contribute to the development of recommended exposure limits and evaluation methods for reaction load exposure from handheld tightening tools. Policymakers could utilize the insights presented in this thesis to form general guidelines directed at power tool manufacturers as well as tool using organizations. Through standardized guidelines, reaction loads from handheld tightening tools, which is one of the contributors to MSDs within assembly work, can be managed and reduced.
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| 6. |
- Palm, Peter, 1975-
(författare)
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Methods to assess physical load at work : With a focus on the neck and upper extremities
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To prevent work-related musculoskeletal disorders (MSDs), useful, reliable and valid methods for assessing physical workload and risks for MSDs are needed. Ergonomists often assess work by short visual observations without a specific tool. A branch-specific tool was developed for assessing working technique during cash register work (BAsiK observation protocol).Inclinometers are an alternative for assessing upper arm postures - over several days. Ergonomists need guidelines explaining how to analyze and interpret such data.The aim was to examine and investigate methods for assessing physical load at work, with focus on the neck and upper extremities.In Paper:I, the reliability and criterion validity of the BAsIK observation protocol were assessed.II, the reliability of risk assessments of repetitive work, based on visual observations performed by 21 ergonomists without a specific tool, was assessed.III, whole-day inclinometer measurements of upper arm elevation were compared between work and leisure, across 13 different occupations – before and after arm elevations during sitting time was excluded.IV, the association between inclinometer-based upper arm elevation and neck/shoulder pain was assessed among 654 blue-collar workers. The intra-observer reliability of the BAsIK protocol was deemed acceptable, but only 3 of 10 questions in the protocol showed acceptable inter-observer reliability, and 3 showed acceptable criterion validity.Neither the inter- or intra-observer reliability of risk assessment without any specific method was acceptable for any upper body regions.None of the occupation groups, in paper III, had higher proportion of time with arm elevation during work than leisure. However, when arm elevation during sitting was excluded, 8 occupation groups had higher proportion of time with elevated arms during work than leisure.Whole-workday inclinometer-based upper arm elevation was not associated with neck/shoulder pain within the assessed population. The results indicate that, in most cases, a single visual observation of a work sequence is not a reliable means of assessing repetitive work. A large proportion of arm elevation may derive from sitting time. At low exposure levels, arm elevation per se may not be a risk factor for neck/shoulder pain.This must be taken into account when evaluating the risk for MSDs.
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| 7. |
- Rhén, Ida-Märta
(författare)
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Ergonomics risk assessment methods for creating healthy work environments
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Risk assessments of ergonomic conditions in pre-production and in field are necessary to prevent work-related musculoskeletal disorders and to increase productivity and quality. Methods for such assessments include simulations, direct measurements and observations. In order to carry out correct ergonomic assessments, which is an important part in the work of creating healthy workplaces, it is vital that these methods are user-friendly, accurate and reliable. However, several methods are insufficiently tested with respect to these factors.The aim of this thesis was to increase the knowledge of some relevant risk assessment methods for the prevention of musculoskeletal disorders. The methods include risk assessments in both planned and existing work environments.A risk assessment approach for digital human modelling was developed. The approach included a reference database of epidemiological relationships between directly measured exposure and related musculoskeletal disorders. For illustration, a case in manual assembly was simulated; exposures were calculated and compared to the reference data to indicate the risk of work-related musculoskeletal disorders. The application and detailed assessment would be helpful to prioritise among different design solutions.A 3D digital prototype of a laparoscopic robotic open console was ergonomically evaluated using the simulation tool Intelligently Moving MAnikins (IMMA); twelve manikins representing anthropometries of the Swedish and US populations were used. The work-ranges of the console and the manikins were calculated and compared. The ergonomics was evaluated using a US checklist and the Swedish standard for computer work. The assessment criteria, which are related to the adjustability of the screen, the armrests, and the pedals, were not fulfilled. The result showed that IMMA, with its built-in functions, provides the opportunity for risk assessment of planned static work tasks. With some improvements, tools like IMMA may increasingly be used efficiently for early assessments of planned products or work environments.The inter- and intra-rater reliability and validity of six observation-based assessment methods, ART, HARM, SI, QEC, OCRA and SWEA, were studied through twelve ergonomists' and an expert group's repeated risk assessments of ten videotaped tasks. The results showed a low to moderate inter- and intra-rater reliability. Both the percent agreement and the reliability differed for the assessments of the methods' overall risk levels. Using a standardised task duration of 3.75 hours (rather than different durations for the different tasks) in the statistical calculations, the reliability of all methods decreased, except for OCRA. The decrease was most evident for HARM and ART, which was due to the fact that the duration of the task has a large impact in the methods' calculation of the total risk level. The validity was similar to the inter-rater reliability for each method.This thesis emphasizes the importance of detailed quantification of exposure and reliable methods to draw accurate conclusions about the risk of musculoskeletal disorders, both in planned and existing work environments.Today's technology, with small and wireless devices for direct measurements and methods for analysing physical exposure, provides opportunities to perform accurate and reliable ergonomic assessments. The possibility of using similar measurement strategies in digital human modelling, allows the discrimination of small differences in exposure which simplifies comparisons of different design solutions as well as between planned and existing work environment. Although the reliability of several observation-based methods was found to be low, observational methods are still important in the risk assessments of physical exposure, in order to include parts of the work environment that are not yet possible to measure. However, observational methods should preferably be used for screening and in combination with technical measurements.
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| 8. |
- Yang, Liyun, 1992-
(författare)
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Ergonomic Risk Assessment and Intervention through Smart Workwear Systems
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The rapid development of wearable technology has provided opportunities to ergonomics research and practice with new ways for workload measurements, data analytics, risk assessment and intervention. This thesis aims at developing and evaluating methods using wearable technologies to assess physical risk factors at work, and further to give feedback to employees to improve their work techniques.One smartphone application (ErgoArmMeter) was developed for the assessment of upper arm postures and movements at work. The application uses integrated signals of the embedded accelerometer and gyroscope, and processes and presents the assessment results directly after a measurement. Laboratory validation with 10 participants was performed using an optical tracking system as standard measurement. The results showed that the application had similar accuracy compared to standard inclinometry for static postures and improved accuracy in dynamic conditions. With its convenience and low cost, the application may be used by researchers and practitioners in various scenarios for risk assessment.Three models for assessment of work metabolism (WM) using heart rate (HR) and accelerometers (ACCs) were evaluated during simulated work tasks with 12 participants against indirect calorimetry as standard measurement. The HR + arm-leg ACC model showed best accuracy in most work tasks. The HR-Flex model showed a small bias for the average of all tasks. For estimating WM in the field using wearable technologies, the HR-Flex model or the HR + arm-leg ACC model may be chosen depending on the need for accuracy level and resource availabilities. Further improvement of the classification algorithm in the HR + arm-leg ACC model is needed in order to suit various types of work.Two smart workwear systems were developed and evaluated. Smart workwear system 1.0 consisted of a sensorized vest, an inertial measurement unit (IMU) and an Android tablet application. It assessed risks of high physiological workload and prolonged occupational sitting/standing. The results were visualized by color-coded risk levels. The system was evaluated with 8 participants from four occupations in a field study. It was perceived as useful, comfortable and not disturbing by most participants. Further development is required for the system for automated risk assessment of various ergonomic risk factors in real work situations.Smart workwear system 2.0 consisted of an instrumented t-shirt with IMUs, vibration units and an Android smartphone application. It provided vibrotactile feedback to users’ upper arm and trunk when predefined angular thresholds were exceeded. The system was evaluated for work postures intervention in industrial order picking among 15 participants. It showed to be effective in improving the trunk and dominant upper arm postures. The system was perceived as comfortable and useful. The vibrotactile feedback was evaluated as supportive for learning regarding workplace and task design among the participants.In conclusion, the research in this thesis showed that wearable technologies can be used both in the laboratory and field for assessment of physical risk factors at work and intervention in work technique improvement. With further research and development, smart workwear systems may contribute to automated risk assessment, prevention of work-related ill health, and improvement of the design and overall quality of work.
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| 9. |
- Zetterberg, Camilla, 1970-
(författare)
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The impact of visually demanding near work on neck/shoulder discomfort and trapezius muscle activity : Laboratory studies
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Introduction: Musculoskeletal discomfort in the neck and shoulders is common among workers performing visually demanding near work, e.g., on a computer screen, and sustained low-level muscle activity during such work can lead to work-related pain. The relationships between visual demands and muscle activity and discomfort in the neck/shoulder region are at present unclear. Aim: The aims of this thesis were to determine whether neck/shoulder discomfort and trapezius muscle activity increases during visually demanding experimental near work, and to investigate whether eye-lens accommodation is a mediating mechanism behind increased trapezius muscle activity. Methods: The four papers included are based on two experiments with different visually demanding near work tasks (duration 5 and 7 min). Trial lenses of different diopters were used to manipulate the visual demands (i.e., induce more or less accommodation) and thereby create different viewing conditions. Monocular viewing, which does not require active convergence, was used to examine the isolated effect of accommodation. Eye-lens accommodation and trapezius muscle activity were measured continuously during the visual tasks, and in one experiment the participants rated their eye and neck/shoulder discomfort at baseline and after each visual task. Results: Neck/shoulder discomfort and trapezius muscle activity increased during the visually demanding near work and participants experiencing a greater increase in eye discomfort (compared with baseline) also developed more neck/shoulder discomfort with time. There were no significant differences in muscle activity among the viewing conditions, and no effect of isolated accommodation response within the monocular viewing conditions. Conclusion: These findings indicate that accommodation per se is unlikely to mediate trapezius muscle activity. Instead, the increase in trapezius muscle activity observed here may be due to a combination of high visual attention and enhanced requirement for eye-neck (head) stabilisation. Since these results suggest that neck/shoulder discomfort may aggravate with time when the visual demands are high, it is important to provide good visual conditions in connection with visually demanding occupations.
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