Workers experience combined physical and mental demands in their daily jobs, yet the contribution of these concurrent demands in the development of work-related musculoskeletal disorders (WMSDs) is not clearly understood. There is a need to understand how concurrent demands interact with different work parameters, such as force levels, muscles employed, and types of exertion, to influence physiological responses. Furthermore, whether muscle capacity is altered with these concurrent demands remains unclear. The current research was conducted to address these needs through three experimental studies that evaluated changes in physiological, performance, and subjective measures. The first study investigated muscle-specific responses to concurrent physical and mental demands during intermittent static work. Mental demands adversely affected physiological responses with increasing physical demand. Furthermore, greater motor and mental performance impairment was observed at either end of the physical demand spectrum. Finally, these interactions were muscle-dependent, with postural (shoulder and torso) muscles indicating a greater propensity to interference due to concurrent demands than executive (wrist) muscles. The aim of the second study was to evaluate differential effects of exertion type (static and dynamic) during concurrent physical and mental work. Concurrent physical and mental demands adversely affected physiological responses during static exertions compared to dynamic exertions. Furthermore, static exertions were more susceptible to decrements in muscle output and mental task performance than dynamic exertions, specifically at higher force levels. The last study quantified the effects of concurrent physical and mental demands on muscle capacity (endurance, fatigue, and recovery) during intermittent static work. Additional mental processing was associated with shorter endurance times, greater strength decline, increased fatigability, and slower cardiovascular recovery. Concurrent demand conditions were also associated with higher levels of perceived fatigue, and rapid increases in rates of perceived exertion, time pressure, mental load, and stress. Overall, the current research provides a comprehensive understanding of the interactive effects of physical and mental demands on physiological responses and task performance. These findings may facilitate the development of task design strategies to help reduce the risk of workplace injuries and to increase worker performance. Finally, outcomes from this research can contribute towards the revision of current ergonomic guidelines to incorporate concurrent assessment of physical and mental demands. / Ph. D.

Workload is defined as the cost incurred by an individual, given their capacities, while achieving a particular level of performance on a task with specific demands. Demands of a task or combination of tasks may include maintaining postural stability, executing physical actions, and/or performing cognitive tasks. While there have been attempts to establish a physiological measure of concurrent physical and mental workload, as yet there has been no work towards developing a single subjective method of evaluation. Select subjective assessment methodologies were evaluated quantitatively during laboratory-based experiments. Concurrent execution of mental and physical activity was required at various levels, since it was desired to be able to measure mental workload, physical workload, and also evaluate their interaction. Measurements of task performance were investigated to evaluate the effects of combined mental and physical demands and establish which subjective assessments were accurate and sensitive to changes in workload. The utility of existing subjective assessment tools created for one domain appeared to be limited when evaluating multi-task situations requiring substantial mental and physical activity. Further clarification of the impact of different types of physical demand on cognitive processing, performance and subjective workload assessment of a constant mental task was addressed in the second experiment. This experiment investigated the effect of several activity types, specifically global versus localized effort, changes in load, and different task frequencies. The results provided support that the type of activity, load and frequency of task influence subjective mental workload assessment scores and performance. Not all existing assessment tools accurately represented an individual's ability to perform a task when there was a combination of physical and mental demands. A unidimensional tool is suggested as a screening tool to identify situations requiring excessive or increased mental workload. Alternative methods, possibly a new multidimensional tool, should be developed to obtain more detailed information so ratings of workload for different tasks may be compared. Effectiveness of a subjective stability assessment tool was evaluated in situations demanding mental activity while maintaining an upright posture. Tests were performed over a wide range of conditions, including various mental loads, sensory conditions, and postural stances. The purpose was to determine the effects of each task variation on the perception of postural stability. Postural sway increased with task difficulty, regardless of the source (i.e. postural stance, visual condition, mental workload). The addition of mental workload did not alter the non-linear relationship between objective measures of postural sway and perceptions of postural stability. Since decrements in balance are well perceived, subjective assessment tools may be incorporated in control strategies to minimize falls. / Ph. D.

Ce travail de recherche s'inscrit dans le contexte d'une étude épidémiologique de cohorte. De septembre 1999 à décembre 2003, une vaste étude longitudinale comportant 2 ans de suivi avait été lancée en Belgique grâce à un financement de la Politique Scientifique Fédérale (PSF). Elle sintitulait: "Etude de cohorte des déterminants étiologiques et pronostiques des maux de dos liés à la profession". Cette étude était conduite par plusieurs centres de recherche . Dans un souci de visibilité internationale, elle porte le nom de BELCOBACK Study (BELgian COhort study on low BACK pain). Comme toute étude épidémiologique, l'étude BELCOBACK vise à mettre en relation l'exposition à une série de facteurs de risque et l'apparition de plaintes en relation avec une problématique de santé. Ainsi, la précision de cette relation dépend à la fois de la précision de l'estimation de l'exposition et de la précision de l'estimation de l'effet santé. Dans le contexte présent, l'effet santé correspond à l'apparition d'un épisode de lombalgie dont l'objectivation est davantage basée sur le symptôme que sur des critères cliniques. Ainsi, en épidémiologie, le questionnaire est bien la méthode de choix pour évaluer la lombalgie. La précision avec laquelle l'exposition est évaluée est moins consensuelle et plus complexe car un plus grand choix de méthodes est possible. Dans ce domaine, les méthodes les plus précises, comme les mesures directes par instrumentation du sujet, sont aussi les plus coûteuses et les plus difficiles à appliquer à un large effectif. Or, dans toute étude épidémiologique, l'effectif doit être important pour des raisons de puissance statistique. En sachant qu'il existe un cadre budgétaire limitatif, il est donc généralement nécessaire d'aboutir à un compromis de "coût-précision" dans le choix des méthodes d'évaluation à mettre en uvre. L'étude BELCOBACK ne faisant pas exception à cette règle, le choix des méthodes d'évaluation est donc au centre de ce travail. L'objectif de celui-ci consiste à évaluer l'exposition professionnelle aux facteurs de risque mécaniques de la lombalgie, en utilisant une méthodologie qui présente une précision suffisante tout en restant dans des limites de coûts acceptables. Un état de la question sera dabord présenté. Il vise à résumer lépidémiologie de la lombalgie dans la population générale et dans la population active, les méthodes dévaluation de la lombalgie, les facteurs de risque professionnels de la lombalgie et leurs méthodes dévaluation. Dans létude BELCOBACK, les deux instruments de mesures retenus pour lévaluation des risques mécaniques de la lombalgie étaient le questionnaire auto-administré et les observations directes. Les deux premiers chapitres sont dès lors consacrés au développement et à la validation de ces instruments. Le dernier chapitre est, quant à lui, consacré à létude des relations entre lincidence des lombalgies et le niveau dexposition évalué par les méthodes développées.

<p><i>Objectives.</i> To study the prevalence of musculoskeletal symptoms among farmers as compared to rural referents and to evaluate the effects of physical work exposures, psychosocial factors, lifestyle and comorbidity.</p><p><i>Material and methods.</i> A cross-sectional population-based survey of 1013 farmers and 769 matched referents was performed. Data on various symptoms, consultations and sick leave and information on primary health care and hospital admissions were obtained along with information on physical workload, psychosocial factors and lifestyle. </p><p><i>Results.</i> The farmers reported higher lifetime prevalence of symptoms from hands and forearms, low back and hips as compared to the referents. However, the farmers did not seek medical advice more often than the referents, and they reported significantly fewer sick leaves. After adjustment for the influence of physical work exposure, farmers still had a excess rate of low back pain (LBP) and hip symptoms as compared with the referents, while a lower rate of neck-shoulder symptoms was revealed. Several of the psychosocial variables were associated with LBP but the difference in LBP prevalence between farmers and referents could only be explained to some extent. LBP was associated with musculoskeletal symptoms other than LBP and with chest discomfort, dyspepsia, symptoms from mucous membranes, skin problems, work-related fever attacks, and primary care for digestive disorders. Presence of both respiratory and digestive disorders doubled the LBP prevalence.</p><p><i>Conclusions.</i> Symptoms from hips and low back were more frequent among farmers than among referents, but farmers did not seek more health care and reported fewer sick leaves than referents. Physical work exposure and psychosocial factors did not explain the differences in low back and hip symptoms between the two groups. Significant associations between LBP and digestive and respiratory disorders might indicate that these disorders may have etiological factors in common.</p>

Objectives. To study the prevalence of musculoskeletal symptoms among farmers as compared to rural referents and to evaluate the effects of physical work exposures, psychosocial factors, lifestyle and comorbidity. Material and methods. A cross-sectional population-based survey of 1013 farmers and 769 matched referents was performed. Data on various symptoms, consultations and sick leave and information on primary health care and hospital admissions were obtained along with information on physical workload, psychosocial factors and lifestyle. Results. The farmers reported higher lifetime prevalence of symptoms from hands and forearms, low back and hips as compared to the referents. However, the farmers did not seek medical advice more often than the referents, and they reported significantly fewer sick leaves. After adjustment for the influence of physical work exposure, farmers still had a excess rate of low back pain (LBP) and hip symptoms as compared with the referents, while a lower rate of neck-shoulder symptoms was revealed. Several of the psychosocial variables were associated with LBP but the difference in LBP prevalence between farmers and referents could only be explained to some extent. LBP was associated with musculoskeletal symptoms other than LBP and with chest discomfort, dyspepsia, symptoms from mucous membranes, skin problems, work-related fever attacks, and primary care for digestive disorders. Presence of both respiratory and digestive disorders doubled the LBP prevalence. Conclusions. Symptoms from hips and low back were more frequent among farmers than among referents, but farmers did not seek more health care and reported fewer sick leaves than referents. Physical work exposure and psychosocial factors did not explain the differences in low back and hip symptoms between the two groups. Significant associations between LBP and digestive and respiratory disorders might indicate that these disorders may have etiological factors in common.

Surgeons have been identified as one of the highest risk groups in healthcare to develop work-related musculoskeletal disorders (WMSDs). Especially the neck and shoulders are found to be at high musculoskeletal risk due to surgeons commonly operating in a static and awkward posture for a prolonged time. Raising ergonomic awareness has been found to favour postural improvement among healthcare professionals. This thesis therefore aimed to design and evaluate an individual ergonomic report as means for risk assessment and ergonomic education for surgeons. Hereby, two surgeons and two ergonomists were included in the design process for early user feedback. Thematic analysis was applied to analyse the user feedback and potential improvements were identified and performed. The final individual ergonomic report was evaluated as a material used in an individual educational session (i.e., the intervention group) and compared against the use of an ergonomic guideline (i.e., the control group). Each group consisted of two surgeons. Both questionnaire and semi-structured interview were used to evaluate the session. The results from the questionnaire showed similarly positive ratings on the user experience of both groups, but higher ratings were given on the perceived impact by the intervention group. The interview results also showed more positive responses by the intervention group in terms of the usability. Furthermore, facilitators and barriers for adopting ergonomic principles were collected from the surgeons. Multiple ways to improve surgical ergonomics as perceived by the surgeons were also identified, e.g., the use of ergonomic equipment, and implementation of stretch breaks in the OR. The results show the potential of an individual ergonomic assessment report as ergonomic intervention for surgeons to raise their awareness and knowledge about ergonomic principles which can contribute to decreasing their risk of developing WMSDs as well as improved surgical performance and patient safety. Future studies can regard further ergonomic risk parameters and incorporate practical instructions on ergonomic principles into educational ergonomic intervention. / Kirurger har identifierats som en av de högsta riskgrupperna inom hälso- och sjukvården att utveckla arbetsrelaterade belastningsskador. Särskilt nacke och axlar har visat sig ha hög risk för belastningsskador på grund av att kirurger ofta arbetar i en statisk och ogynnsam kroppsställning under en längre tid. Att öka den ergonomiska medvetenheten har visat sig gynna en förbättring av arbetsställning bland vårdpersonal. Denna avhandling syftade därför till att utforma och utvärdera en individuell ergonomisk rapport som ett medel för riskbedömning och ergonomisk utbildning bland kirurger. Två kirurger och två ergonomer deltog i designprocessen och tidig användarfeedback samlades. Tematisk analys användes för att analysera användarfeedback och potentiella förbättringar identifierades och genomfördes. Den slutliga individuella ergonomirapporten utvärderades som ett material som användes i en individuell utbildningssession (dvs interventionsgruppen) och jämfördes med användningen av en broschyr på kirurgergonomi (dvs kontrollgruppen). Varje grupp bestod av två kirurger. Både frågeformulär och semistrukturerad intervju användes för att utvärdera utbildningssessionen. Resultaten från frågeformuläret visade lika positiva användarupplevelse betyg från båda grupperna, men högre betyg gavs på den upplevda effekten av interventionsgruppen. Dessutom identifierades faciliteter och barriärer för att anta ergonomiska principer från kirurgerna. Flera sätt att förbättra kirurgisk ergonomi som uppfattades av kirurgerna identifierades också, till exempel användning av ergonomisk utrustning och implementering av sträcknings pausar i operationssalen. Resultaten visar att individuell ergonomisk bedömningsrapport som ergonomisk intervention för kirurger har potential för att öka medvetenhet och kunskap om ergonomiska principer. Detta kan bidra till att minska kirurgers risk att utveckla arbetsrelaterade belastningsskador samt förbättrad kirurgisk prestanda och patientsäkerhet. Framtida studier kan ta hänsyn till ytterligare ergonomiska riskparametrar och införliva praktiska instruktioner om ergonomiska principer i pedagogisk ergonomisk intervention.