This study examined an existing industrial workstation at an automobile assembly plant using computer aided ergonomics and digital human models. The purpose of this evaluation was the development of a methodology useful for evaluating workstations to identify potential design issues that could result in musculoskeletal injury in a real work environment. An ergonomic risk assessment was conducted on a lifting task while being performed both manually and using an assist device. JACK digital human modeling and ergonomics software were used to conduct a computer-based ergonomic analysis. Four analysis tools in JACK (static strength analysis, rapid upper limb assessment, metabolic energy expenditure analysis and NIOSH lift analysis) were used to evaluate the potential injury risk of the current method of task performance and there is any difference between using and not using the assist device. Muscle activity was measured by electromyography (EMG) to identify physiological indicators of fatigue. Also, Borg¡¯s Rate of Perceived Exertion (RPE) scale was administered to obtain psychophysical data. Results of this study revealed that there were relative stresses on the trunk and arm areas when the task was performed manually. The results also suggest although using the assist device decreased injury risk potentially, use of the assist device had an adverse impact on the productivity of the assembly line. Based on the findings of this study, the methodology used appears to be an appropriate ergonomic analysis tool for assessing and predicting potential risks associated with the design of industrial workstations. Furthermore this methodology can be extended to designing and redesigning industrial workstations.

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Prior studies have reported differences in lower back biomechanics during activities of daily living between individuals with and without chronic low back pain (LBP). Nevertheless, the literature on lower back biomechanics of patients with non-chronic LBP is scant. Therefore, the objective of this study, as the first step towards future prospective studies, was to investigate the lower back biomechanics in patients with non-chronic LBP. Case-control studies were conducted wherein measures of lumbo-pelvic coordination during bending and return tasks as well as measures of mechanical demand on the lower back during lifting tasks in the sagittal plane were investigated between patients with non-chronic LBP and matched asymptomatic individuals. Patients were enrolled into the study at the non-chronic stage of their LBP. We found distinct difference in measures of lumbo-pelvic coordination as well as mechanical demands on the lower back between patients with non-chronic LBP and controls. Reduced lumbar range of flexion and slower task pace as well as the more in-phase and less variable lumbo-pelvic coordination observed in patients with non-chronic low back pain, may be the result of a neuromuscular adaptation to reduce the forces and deformation in the lower back tissues and avoid pain aggravation. Such a neuromuscular adaptation, however, resulted in a larger shearing demand on the lower back. Persistent abnormal lumbo-pelvic coordination might play a role in transition to chronic stage or recurrence of LBP. However, such inferences need to be further investigated using prospective studies as well as clinical trials involving a combination of physical and psychological treatments aimed at correction of lumbo-pelvic coordination.

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Thèse de doctorat à mi-chemin entre la recherche fondamentale et appliquée. Les champs disciplinaires sont principalement la biomécanique, l'ergonomie physique ou encore l'anatomie. Réalisé en cotutelle avec le professeur Paul Allard et Mickael Begon. / An occupation that requires handling loads combined with large elevation of the arms is associated with the occurrence of shoulders musculoskeletal disorder. The analysis of these joint movements is essential because it helps to quantify the stress applied to the musculoskeletal structures. This thesis provides an innovative model which allows the estimation of the shoulder complex kinematics and used it to analyze the joints kinematics during lifting tasks. It is organized into three sub-objectives. The first aim is the development and validation of a kinematic model the most representative as possible of the shoulder complex anatomy while correcting soft tissue artifacts through the use of global optimization. This model included a scapulothoracic closed loop, which constrains a scapular dot contact to be coincident with thoracic gliding plane modeled by a subject-specific ellipsoid. In the validation process, the reference model used the gold standard for direct measurements of bone movements. In dynamic movements, the closed loop model developed generates barely more kinematic errors that errors obtained for the study of standard movements by existing models. The second aim is to detect and quantify the shoulder articular movements influenced by the combined effects of two risk factors: task height and load weight. The results indicate that many peaks of joint angles are influenced by the interaction of height and weight. According to the different initial and deposits heights when the weight increases, the kinematics changes are substantial, in number and magnitude. The kinematic strategies of participants are more consistent when the weight of load increase for initial height lift at hips level compared to shoulders level, and for a deposit at eye level compared to shoulders. The third aim is to investigate the magnitude and temporality of the maximum peak vertical acceleration of the box. The significant joints movements are characterized with a principal component analysis of joint angle values collected at this instant. In particular, this study highlights that elbow flexion and thoraco-humeral elevation are two correlated invariant joint movements to all lifting tasks whatever the initial and deposit height, and weight of the load. The realism of the developed shoulder model and kinematics analyzes open perspectives in occupational biomechanics and contribute to risk prevention efforts in health and safety. / Une activité professionnelle qui exige de manipuler des charges combinée à de grandes élévations des bras augmente les chances de développer un trouble musculo-squelettique aux épaules. L’analyse de ces mouvements articulaires est essentielle car elle contribue à quantifier les contraintes appliquées aux structures musculo-squelettiques. Cette thèse propose un modèle innovant qui permet l’estimation de la cinématique du complexe de l’épaule, et l’utilise ensuite afin d’analyser la cinématique de levers de charge. Elle s’organise en trois sous-objectifs. Le premier concerne le développement et la validation d’un modèle cinématique le plus représentatif possible de l’anatomie du complexe de l’épaule tout en corrigeant les artéfacts des tissus mous par une optimisation multi-segmentaire. Ce modèle avec une fermeture de boucle scapulo-thoracique, impose à un point de contact scapulaire d’être coïncident au plan de glissement thoracique modélisé par un ellipsoïde mis à l’échelle pour chaque sujet. Le modèle qui a été utilisé comme référence lors des comparaisons du processus de validation bénéficie du « gold standard » de mesures directes des mouvements osseux. Le modèle développé en boucle fermée génère à peine plus d’erreurs cinématiques lors de mouvements dynamiques que les erreurs obtenues par les modèles existants pour l’étude de mouvements standards. Le second identifie et quantifie les mouvements articulaires de l’épaule influencés par la combinaison des effets de deux facteurs de risques : les hauteurs importantes d’agencement de la tâche (hauteurs de saisie et de dépôt) et les masses de charges (6 kg, 12 kg et 18 kg). Les résultats indiquent qu’il existe de nombreux pics d’angles articulaires qui sont influencés par l’interaction des deux effets. Lorsque la masse augmente, les modifications cinématiques sont plus importantes, en nombre et en amplitude, selon les différentes hauteurs de saisies et de dépôts de la charge. Les participants varient peu leur mode opératoire pour une saisie à hauteur des hanches en comparaison des épaules, et pour un dépôt à hauteur des yeux en comparaison aux épaules avec une charge plus lourde. Un troisième s’intéresse au pic maximal d’accélération verticale de la charge dans son intensité et sa temporalité. Basée sur une analyse en composante principale des valeurs d’angles articulaires à cet instant, elle permet de caractériser les mouvements articulaires significatifs. Cette étude met notamment en évidence que la flexion du coude et l’élévation thoraco-humérale sont deux mouvements articulaires corrélés invariants à toutes les tâches de lever en hauteur quelles que soient la hauteur de dépôt et la masse de la charge. Le souci de réalisme du modèle développé et les analyses cinématiques menées ouvrent des perspectives en biomécanique occupationnelle et participent à l’effort de prévention des risques en santé et sécurité.