Studies have shown that modeling errors due to unaccounted for soft-tissue deformations – known as soft-tissue artifact (STA) – can reduce the efficacy and usefulness of musculoskeletal simulations. Recent work has proven that adding degrees of freedom (DOF) to the joint definitions of a musculoskeletal model’s lower limbs can significantly change the prediction of an individual’s kinematics and dynamics while simultaneously improving estimates of their mechanical work. This indicates that additional modeling complexity may mitigate the effects of STA. However, it remains to be determined whether adding DOF to the lower limb joints can impact a model’s satisfaction of Newton’s Second Law of Motion, or whether a specific number of DOF must be incorporated in order to produce the most biomechanically accurate simulations. To investigate these unknowns, I recruited ten subjects of variable body-mass-indices (BMI) and recorded subject walking data at three speeds normalized by Froude number (Fr) using optical motion capture and an instrumented treadmill (eight male, two females; mean ± s.d.; age 21.6 ± 2.87 years; BMI 25.1 ± 5.1). Then, I added DOF to the lower limb joints of OpenSim’s 23 DOF lower body and torso model until it minimized the magnitude of the pelvis residual forces and moments for a single, representative subject trial (BMI = 24.0, Fr = 0.15). These artificial residual forces and moments are applied at the pelvis to maintain the model’s orientation in space by satisfying Newton’s Second Law. Finally, I simulated all 30 trials with both the original and the edited model and observed how the biomechanical predictions of the two models differed over the range of subject BMIs and walking speeds. After applying both the original and the edited model to the entire data set, I found that the edited model resulted in statistically lower (α = 0.05) residual forces and moments in four of the six directions. Then, after investigating the impact of changes in BMI and Froude number on these residual reductions, I found that two of the six directions exhibited statistically significant correlations with Froude number while none of the six possessed correlations with BMI. Therefore, adding DOF to the lower limb joints can improve a model’s dynamic consistency and combat the effects of STA, and simulations of higher speed behaviors may benefit more from additional DOF. For BMI, it remains to be determined if a higher BMI indicates greater potential for residual reduction, but it was shown that this method of tuning the model for one representative subject was agnostic to BMI. Overall, the method of tuning the model for one representative subject was found to be quite limited. There were multiple subject trials for which reduced residuals corresponded to drastic changes in kinematic and dynamic estimates until they were no longer representative of normal human walking. Therefore, it is possible to improve dynamic consistency by adding DOF to the lower limb joints. But, for biomechanically relevant estimates to be consistently preserved and soft-tissue artifact to be completely minimized, subject-specific model tuning is likely necessary. / Mechanical Engineering

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Locomotion is one of the most important qualities of man and has always been associated with survival, foraging ans subsistence. During the course of evolution, men and women developed some form of gender specialization which resulted in different level of mobility between the sexes. Throughout history, the types of subsistence have changed and the degree of sedentism has increased. However, despite all the changes in subsistence, gender specialization and bone robusticity sexual dimorphism in the robusticity of the lower limb bones remained surprisingly stable. Is it possible that women load lower limb bones differenty than men (e.i. due to different body proportions)? The aim of this work is to determine wheter there is sexual dimorphism between the sexes of the recent living population in the cross-sectional properties of the tibia and in the load on the tibia during running. In this work we used images of the tibia from magnetic resonance imaging and kinematic and kinetic data during the run of 20 probands. By using musculoskeletal modeling we estimated the bending moment acting at 50 % of the tibial length as well as the angle of action of this moment. After adjusting for size, no significant difference was found in the results of cross-sectional geometry of the bone in any of the monitored...

L’étude de la biomécanique de la locomotion en fauteuil roulant manuel (FRM) a pour objectif de limiter le risque d’apparitions de blessures du membre supérieur, en optimisant la facilité à se déplacer. De nombreuses études ont montré qu’un ajustement des réglages du FRM avait un impact sur la mobilité. Néanmoins, les modèles utilisés dans la littérature pour représenter les interactions « sujet-FRM » et « FRM-environnement » possédaient plusieurs limitations. Ainsi, l’objectif premier de la thèse était la mise en place d’un modèle musculo-squelettique du membre supérieur permettant de modéliser l’interaction entre le sujet et le FRM, en utilisant des méthodes expérimentales adaptées pour appliquer ce modèle. Le second objectif était de construire un modèle mécanique du FRM en mouvement permettant de calculer les forces de réaction entre le sol et les roues du FRM. Le dernier objectif était d’appliquer une procédure d’optimisation numérique des réglages du FRM incluant les modèles développés durant la thèse. Le modèle musculo-squelettique développé a permis d’analyser la biomécanique du membre supérieur lors de la locomotion en FRM chez les sujets recrutés lors des campagnes de mesures. L’optimisation des réglages du FRM a été mise en place à partir du modèle mécanique du FRM, permettant de confirmer l’influence de plusieurs réglages sur la mobilité en FRM. Enfin, des perspectives d’amélioration de la procédure d’optimisation des réglages ont été explorées, à partir d’algorithmes de génération prédictive du mouvement. / The study of manual wheelchair (MWC) locomotion biomechanics aims at lowering the risk of upper limbs injuries, by optimizing mobility. Several studies have showed that adjusting MWC settings had an impact on MWC mobility. However, the models used in the literature to depict the « user-MWC » and « MWC-floor » interactions had several limitations. Thus, the first aim of this thesis was to develop a musculoskeletal model of the upper limbs allowing to describe the « user-MWC » interaction, by using adapted experimental methods to apply this model. The second aim of the thesis was to implement a mechanical model of the MWC allowing to compute ground reaction forces during locomotion. The final aim of the thesis was to apply a numerical optimisation procedure, including the models developed during the thesis, to optimize MWC settings. The musculoskeletal model developed during the thesis allowed to analyze biomechanics of the upper limbs during MWC locomotion among subjects recruited during experimental sessions. The MWC settings optimization was implemented with the mechanical model developed during the thesis and confirmed the influence of various MWC settings on mobility. Eventually, improvement perspectives for the numerical optimization procedure of MWC settings were explored, based on predictive movement generation with optimal control algorithms.

The muscle force determines the energy costs of locomotion and the loading of the musculoskeletal system. As the body size increases, the muscle force increases too. The observed less joint flexion in larger individuals could be a moderating mechanism to reduce muscle force when walking. To date, there is a lack of knowledge about the effect of body size and joint angles on muscle force. The aim of this study was to investigate how body size affects muscle force in the stance phase of walking and whether larger individuals can effectively compensate for the increase in muscle force through postural changes. We acquired kinematic, kinetic and electromyographic data for 19 men during normal walking and carrying additional 20 % of body weight. We estimated muscle force using the method of musculoskeletal modeling. We emploeyd the multiple linear regression to asses independent effect of body mass, lower limb length, biiliac breadth and joint flexion angle on total (iF) and maximum (maxF) lower limb muscle force. The body mass had a great positive effect on the gluteus medius muscle force (maxF and iF) but did not affect the iliopsoas muscle force (maxF and iF) nor the vasti muscles force (iF). The lower limb length had a positive effect on the gluteus maximus muscle force (maxF) and a negative effect...

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One of the causes of work-related Musculoskeletal Disorders (MSDs) is the manual handling of heavy objects. To reduce the risk of such injuries, workers are instructed to follow general guidelines on how to lift and carry objects depending on their mass. Current ergonomic assessments using wearable sensors can differentiate correct from incorrect body postures but are limited. Being able to estimate the mass of an object during ergonomic assessment would be a great improvement. This work investigates a combination of Inertial Measurement Units (IMUs) and Electromyography (EMG) sensors for offline estimation of an object’s mass for different movements. 10 participants performed 26 lifting and carrying trials with loads from 0 to 19 kg, while wearing a 17IMU motion capture system and EMG sensors on both biceps brachii and both erector spinae. Two methods were considered to estimate the carried mass: (1) supervised machine learning and (2) musculoskeletal modeling. First, the data was used to select features, train, and compare regression models. The lowest Mean Squared Error (MSE) for 10-fold cross-validation for lifting and carrying combined was 5.8113 for a Gaussian Process Regression (GPR) model with an exponential kernel function. Then, a MSE of 4.42 and a Mean Absolute Error (MAE) of 1.63 kg were obtained also with a GPR for Leave-One-Subject-Out Cross-Validation (LOSOCV) only for lifting and frontal carrying trials. For the same trials, the upper-extremity musculoskeletal model, scaled to each participant, estimated the mass with a MSE of 1.78 and a MAE of 0.95 kg. The study was restricted to lifting and frontal carrying, but the combination of the two technologies showed great potential for object mass estimation.

Le corps humain possède une grande redondance musculo-squelettique, se traduisant par une infinité de coordinations musculaires possibles pour produire un effort résultant. Lors d'un mouvement, le système nerveux central est confronté à la gestion de cette redondance. A travers l’analyse de cohérence entre les signaux électromyographiques, ce travail de thèse étudie le rôle fonctionnel du couplage intermusculaire et explore la contribution des mécanismes nerveux impliqués dans la régulation de la redondance musculaire en termes de contrôle de l’activité des muscles agonistes, et antagonistes impliqués dans le phénomène de co-contraction. Nos résultats ont révélé que le couplage intermusculaire entre deux muscles agonistes est modulé en présence de fatigue et en fonction de l’expertise sportive. De plus, le couplage entre muscles agonistes et antagonistes dépend des contraintes mécaniques et du rôle fonctionnel des muscles, et semble directement lié au niveau de co-contraction. La cohérence intermusculaire est modulée dans plusieurs bandes de fréquence, témoignant de l’implication de différentes commandes centrales communes d’origines spinales et supra-spinales. Nos conclusions amènent à penser que la coordination musculaire est en partie contrôlée par des commandes nerveuses communes dont la contribution est modulée suivant les propriétés fonctionnelles des muscles concernées, pour s’adapter de manière optimale aux contraintes internes ou externes de la tâche. Les travaux déjà engagés proposent de contribuer à une meilleure compréhension des mécanismes sous-jacents l’altération de la fonction motrice chez des patients cérébro-lésés. / The human motor system is characterized by high musculoskeletal redundancy, implying that a given resultant effort can result from infinity of feasible muscle coordinations. During a movement, the central nervous system has to manage such redundancy. Through coherence analysis between electromyographic signals, this thesis work aims at investigating the functional role of intermuscular coupling and at better understanding the contribution of central nervous mechanisms responsible for the regulation of muscle redundancy, in terms of agonist muscle activity and also antagonist muscles activity involved in co-contraction. Our results revealed that intermuscular coupling between agonist muscles is modulated according to both the fatigue level and the training status. We also showed that the coupling between agonist and antagonist muscles depends on the mechanical configuration and functional role of muscle pairs, and seems directly related to co-contraction. The modulation of intermuscular coherence occurs in several frequency bands, suggesting the involvement of different common central drives of spinal and supra-spinal origins according to task constraints. Taken together, our results lead us to conclude that common neural drives take part in the control of muscular coordination, with different relative contribution according to the functional properties of recruited muscles, in order to optimally adapt to both internal and external task contraints. Work already undertaken proposes to provide a better understanding of the mechanisms underlying impairment of motor function in brain-injured patients.