Thèses sur le sujet « Mechanical movements Biomechanics »

Study of physical phenomena by means of mathematical models is common in various branches of engineering and science. In biomechanics, modelling often involves studying human motion by treating the body as a mechanical system made of interconnected rigid links. Robotics deals with similar cases as robots are often designed to imitate human behavior. Modelling human movements is a complicated task and, therefore, requires several simplifications and assumptions. Available computational resources often dictate the nature and the complexity of the models. In spite of all these factors, several meaningful results are still obtained from the simulations.

One common problem form encountered in real life is the movement between known initial and final states in a pre-specified time. This presents a problem of dynamic redundancy as several different trajectories are possible to achieve the target state. Movements are mathematically described by differential equations. So modelling a movement involves solving these differential equations, along with optimization to find a cost effective trajectory and forces or moments required for this purpose.

In this study, an algorithm developed in Matlab is used to study dynamics of several common human movements. The main underlying idea is based upon temporal finite element discretization, together with optimization. The algorithm can deal with mechanical formulations of varying degrees of complexity and allows precise definitions of initial and target states and constraints. Optimization is carried out using different cost functions related to both kinematic and kinetic variables.

Simulations show that generally different optimization criteria give different results. To arrive on a definite conclusion on which criterion is superior over others it is necessary to include more detailed features in the models and incorporate more advanced anatomical and physiological knowledge. Nevertheless, the algorithm and the simplified models present a platform that can be built upon to study more complex and reliable models.

La biomécanique du sport décrit le mouvement humain dans le but d'améliorer la performance et de réduire les blessures. Dans ce contexte, le but des experts des sciences sportives est de fournir aux entraîneurs et médecins des informations fiables sur la technique des athlètes. Le manque de méthodes permettant l'évaluation des athlètes sur le terrain ainsi que l'estimation précise des efforts articulaires représente, à ce jour, une limitation majeure pour atteindre ces objectifs. Les travaux effectués dans la thèse vise à contribuer au développement des ces méthodes. Deux approches complémentaires ont été adoptées: une Approche à Basse Résolution - relative à l'évaluation de la performance - où l'utilisation de capteurs inertiels portables est exploitée au cours des différentes phases de la course de vitesse, et une Approche à Haute Résolution - lié à l'estimation des efforts articulaires pour la prévention des blessures - où des contraintes personnalisées pour la modélisation cinématique du genou dans le contexte des techniques d'optimisation multi-corps ont été définies. Les résultats obtenus par l'Approche à Basse Résolution indiquent que, en raison de leur portabilité et leur faible coût, les capteurs inertiels sont une alternative valable aux instrumentations de laboratoire pour l'évaluation de la performance pendant la course de vitesse. En utilisant les données d'accélération et de vitesse angulaire, l'inclinaison et la vitesse angulaire du tronc, la vitesse horizontale instantanée et le déplacement du centre de masse, ainsi que la durée de la phase d'appui et du pas ont été estimés. En ce qui concerne l'Approche à Haute Résolution, les résultats ont montré que les longueurs du ligament antérieur croisé et du latéral externe diminuaient, alors que celle du faisceau profond du ligament latéral interne augmentait de manière significative lors de la flexion. Les variations de longueur du ligament croisé postérieur et du faisceau superficiel du ligament latéral médial étaient de l'ordre de l'indétermination expérimentale. Un modèle mathématique a été fourni qui a permis l'estimation des longueurs ligamentaires personnalisées en fonction de la flexion du genou et qui peuvent être intégrées dans une procédure d'optimisation multi-corps.

Is osteoarthritis a fate unconditionally vested in genetic makeup, or are joints aggravated into inflammation by the way they are treated? Humans are a complicated conglomeration of experiences, decisions, and inheritance. Osteoarthritis, likewise, has evaded simplicity in any explanation of its causation, so it necessitates a multi-dimensional perspective. This research considers the relevance of Alexander Technique in filling a void in which treatment and management of osteoarthritis is not equally equipped to answer this multi-dimensional causation. Alexander Technique is classified as a movement therapy, but this does not quite encompass the mindset of it—that it is indeed largely a mindset about movement. More concisely, Alexander Technique emphasizes self-awareness about how a person uses his or her body to perform daily tasks. It is physical minimalism, and involves continual recognition of muscle tension along with the ability to let go of any tension that is burdensome and unnecessary. This technique has diminished pain and increased the ease of movement for those who have experienced it, even people with osteoarthritis. To build the argument that osteoarthritis can be hindered through a heightened consideration of how joints are treated, the initial component of this research investigated the vast amount of information already gleaned about the pathogenesis of this disease. The fields of physiology, genetics, immunology, and clinical practice already have much to share, and this knowledge has been combined with studies about the benefits and goals of Alexander Technique to discover the common ground of osteoarthritis treatment. The experimental component assesses the association of Alexander Technique to the minimization of pain from osteoarthritis. An online survey asks osteoarthritis cohorts about the history of their disease, the effect it has had on their pain levels and activities of daily living, and about the efficacy of their management strategies. Because each participant will be asked if he or she has received Alexander Technique lessons, the survey can be used to analyze each respondent’s experience of osteoarthritis with respect to that. It was found that participants who had received Alexander Technique lessons reported an average of one more pain-free day per week, and experienced diminished pain levels for daily physical activities such as walking. Management strategies also indicated the benefit of Alexander Technique; those who had taken lessons less frequently used pain and anti-inflammatory medications and were able to be more physically active than the unexposed group. No statistical significance was achieved from the data, largely owing to small sample size (Alexander Technique, n=12, no Alexander Technique, n=25). This study is a step in the direction of better osteoarthritis management, promoting prevention-minded awareness of joint use and providing preliminary fuel for more extensive research.

Cell migration involves complex mechanical interactions between cells or between cells and the underlying substrate. Using a newly developed technique, "traction force microscopy", I have been able to visualize the dynamic characteristics of mechanical forces exerted by migrating fibroblasts such as magnitude, direction, and shear. For NIH 3T3 fibroblasts, I found that the lamellipodium provides nearly all of the force necessary for cell migration. A high shear zone separates the lamellipodium from the remainder of the cell body, suggesting that they are mechanically distinct entities. The timing of the tractions at the leading edge, as well as the spatial distribution, bears no apparent relationship to concurrent local protrusive activities, yet changes in traction force patterns often precede changes in migration direction. In H-ras transformed cells I found isolated regions of weak, transient traction forces in pseudopods all along the cell that appeared to act against one another. The resulting shear pattern suggested that there were multiple disorganized mechanical domains. These results support a frontal towing model for cell migration where the dynamic traction forces at the leading edge served to actively pull the cell body forward. In H-ras transformed cells, the weak poorly coordinated traction forces coupled with weak cell substrate-adhesions were likely responsible for the abnormal motile behavior of these cells. To probe the mechanical interactions beneath various regions of migrating fibroblasts, a cell substrate inhibitor (GRGDTP peptide) was locally applied while imaging stress distribution on the substrate utilizing traction force microscopy. I found that both spontaneous and GRGDTP induced detachment of the trailing edge resulted in extensive cell shortening with no change in overall traction force magnitude or cell migration. Conversely, leading edge disruption resulted in a dramatic global loss of traction forces pnor to any significant cell shortening. These results suggested that fibroblasts transmit their contractile forces to the substrate through two distinct types of adhesions. Leading edge adhesions were unique in their ability to transmit active propulsive forces whereas trailing end adhesions created passive resistance during cell migration and readily redistributed their loads upon detachment. I have also investigated how fibroblasts regulate traction forces based on mechanical input. My results showed that stretching forces applied through the flexible substrate induced increases in both intracellular calcium concentration and traction forces in fibroblasts. Treatment with gadolinium, a well known stretch-activated ion channel inhibitor, was found to inhibit both traction forces and cell migration without inhibiting cellular spread morphology or protrusive activities. Gadolinium treatment also caused a pronounced decrease in vinculin and phosphotyrosine concentrations from focal adhesions. Local application of gadolinium to the trailing region had no detectable effect on overall traction forces or cell migration, whereas local application to the leading edge caused a global inhibition of traction forces and an inhibition of migration. These observations suggest that stretch activated entry of calcium ions in the frontal region serves to regulate the organization of focal adhesions and the output of mechanical forces. Together my experiments elucidate how fibroblasts exert mechanical forces to propel their movements, and how fibroblasts utilize mechanical input to regulate their movements.

The majority of previous research investigating the role of vision in controlling adaptive gait has predominantly focused on over-ground walking or obstacle negotiation. Thus there is a paucity of literature investigating visuomotor control of step descent. This thesis addressed the importance of the lower visual field (lvf) in regulating step descent landing control, and determined when visual feedback is typically used in regulating landing control prior to/during step descent. When step descents were completed from a stationary starting position, with the lvf occluded or degraded, participants adapted their stepping strategy in a manner consistent with being uncertain regarding the precise location of the foot/lower leg relative to the floor. However, these changes in landing control under conditions of lvf occlusion were made without fundamentally altering stepping strategy. This suggests that participants were able to plan the general stepping strategy when only upper visual field cues were available. When lvf was occluded from either 2 or 1 step(s) prior to descending a step during on-going gait, stepping strategy was only affected when the lvf was occluded in the penultimate step. Findings suggest that lvf cues are acquired in the penultimate step/few seconds prior to descent and provide exproprioceptive information of the foot/lower leg relative to the floor which ensures landing is regulated with increased certainty. Findings also highlight the subtle role of online vision used in the latter portion of step descent to 'fine tune' landing control.

Le développement et la médiatisation du sport de haut niveau, notamment en fauteuil roulant, ont changé l 'image du handicap et favorisé le développement d'infrastructures permettant la pratique handisport, reconnue comme bénéfique pour la santé physique et psychique des personnes handicapées...Dans ce contexte, en partenariat avec un joueur de tennis fauteuil de haut niveau, l'objet de ces travaux a été d'étudier l'influence des réglages du fauteuil roulant sur son comportement en match, afin de l'optimiser pour le sport concerné. Ces travaux se concentrent d'abord sur les résistances au mouvement, en particulier dans les paliers des roues, lors du roulement en ligne droite et en rotation. La méthode consiste à créer d'abord un modèle mécanique représentatif du mouvement pour ensuite le valider avec une série d'expérimentations et l'exploiter. L'étude du sportif en mouvement sur son fauteuil a nécessité l'adaptation d'un modèle volumique à une personne assise, avec estimation des paramètres inertiels par mesures rapides. Ce modèle a été appliqué à l'étude de la propulsion à vitesse maximale, pour vérifier l'influence de la position du siège sur ce mouvement. Enfin une étude expérimentale des paramètres influant sur la rotation du fauteuil a mis en avant la forte influence de la position du centre de gravité du sujet sur la rotation, corroborée par un modèle mécanique.Les résultats issus de ces travaux ont permis de mieux comprendre les influences des réglages sur le comportement du fauteuil, de modifier certains réglages pour le sportif et d'orienter la conception d'un nouveau fauteuil. Ces études ont par ailleurs eu des retombées sur les fauteuils conventionnels et entre temps, notre sportif est devenu N°1 mondial
The development of Paralympics has done a lot for a more positive image of handicap and has opened up new opportunities for the practice of disability sport, known to be highly beneficial for the physical and psychological health of disabled people. Conducted in close partnership with a high level tennis player, this study focuses on the influence of the wheelchair settings on its behavior in order to adapt this behavior to wheelchair tennis playing. The study first highlighted the forces of resistance to straight line or rotating wheelchair movements, thanks to mechanical models validated by experiments. Then, the inertial parameters of the seated player's body segments were assessed by adapting a volumic model to the sitting position, and his propulsion at maximal velocity was studied, in order to understand the effect of the seat fore-and-aft position on this movement. Then, an experimental study proved the major influence of the center of gravity position on free rotation, which was modelized too.In a nutshell, this research work has led to a better understanding of the effects of the wheelchair settings on its behavior, its results have allowed to modify various settings on our partner's wheelchair and can be used as a basis for future wheelchair conception/design. They have also proved useful for conventional wheelchairs and in the meantime, our tennis player partner has become wheelchair tennis world champion…

Exoskeletons for rehabilitation commonly focus on gait training, despite the variety of human movements and functional assistance needed. Cable-driven exoskeletons have an advantage in addressing a variety of movements by being non-restrictive in their design. Additionally, these devices do not require complex mechanical joints to apply forces on the user or hinder the user's mobility. This accommodation of movement makes these cable-driven architectures more suitable for everyday movement. However, these flexible cable-driven exoskeletons often actuate a reduced number of actuated degrees-of-freedom to simplify their mechanical complexity. There is a need to design flexible and low-profile cable-driven exoskeletons to accommodate the movement of the user and be more flexible in their ability to actuate them. This thesis presents cable-driven exoskeleton designs that are used during walking and or squatting. These exoskeletons can be reconfigured to apply forces that are appropriate for these functional tasks. The three designs presented in this thesis are non-restrictive cable-driven designs that add minimal weight to the user. The first design shown is the cable-driven active leg exoskeleton previously developed by the Robotics and Rehabilitation Laboratory (C-ALEX, 10kg). The second and third designs are novel cable-driven architectures: (i) the modular C-ALEX (mC-ALEX, 3kg) and (ii) the soft C-ALEX (SC-ALEX, <1kg). A preliminary evaluation of the latter two devices was performed, and the results of these studies are presented to better understand the limitations and abilities of each design. The functionalities added to the latter two designs include the ability to reconfigure the robot's cable routing and attachment geometry, allowing the devices to apply torques through cables in the non-sagittal plane. These features will enable the robot to assist in tasks other than gait while still using the original C-ALEX design methods. Another feature added to the exoskeleton controller is to allow visual feedback through an Augmented Reality headset (the HoloLens) to incorporate visual feedback during tasks better. This feature is currently missing from the rehabilitation field using exoskeletons. The effects of using the C-ALEX with post-stroke participants were carried out to ascertain the efficacy of using a cable-driven system for gait adaptations in persons with gait impairments and compare their effectiveness against rigid-linked exoskeletons. The C-ALEX was assessed to induce a change in the walking patterns of ten post-stroke participants using a single-session training protocol. The ability of C-ALEX to accurately provide forces and torques in the desired directions was also evaluated to compare its design performance to traditional rigid-link designs. Participants were able to reach 91% ± 12% of their target step length and 89% ± 13 % of their target step height. The achieved step parameters differed significantly from participant baselines (p <0.05). To quantify the performance, the forces in each cable's out-of-the-plane movements were evaluated relative to the in-plane desired cable tension magnitudes. This corresponded to an error of under 2Nm in the desired controlled joint torques. This error magnitude is low compared to the system command torques and typical adult biological torques during walking (2-4%). These results point to the utility of using non-restrictive cable-driven architectures in gait retraining, in which future focus can be on rehabilitating gait pathologies seen in stroke survivors. Visual and force feedback are common elements in rehabilitation robotics, but visual feedback is difficult to provide in over-ground mobile exoskeleton systems. A preliminary study was carried out to assess the effects of providing force-only, force and visual, or visual-only feedback to three independent groups, each containing 8 participants. The groups showed an increase in normalized step height, (force and visual: 1.10 ± .13, force-only: 1.03 ± .23 visual-only: 1.61 ± .52) and decreased normalized trajectory tracking error (force and visual: 42.8% ± 23.4%, force: 47.6% ± 18.4% , visual-only: 114.2% ± 60.0%). Visual normalized step height differed significantly from force and visual and force-only normalized step height (p<0.005). Lap-wise normalized tracking error differed significantly ($p < 0.005$) within participants. The mC-ALEX and the HoloLens were used to test the effectiveness of robot force feedback compared to visual feedback with a squat task. The squat task aimed to have the user reach targets of 25%, 75%, and 125% of baseline squats depths through each feedback modality. The kinematic and foot loading effects were considered to establish the differences in user behavior when receiving both types of feedback. The results show that visual feedback has lower errors from targets with similar lower variability in user performance. The force feedback changed joint flexion profiles without changing foot loading biomechanics. When looking at the sessions in sequence, both feedback modalities reduced depth error magnitudes further along with the sessions time-wise. This is the first study where augmented in-field-of-view visual feedback and robotic feedback are used with the aim of changing the kinematics of a squatting task. Overall, this thesis contributes to expanding the capabilities of cable-driven exoskeletons in lower limb rehabilitative tasks. Three designs are evaluated to understand their on-user performance, with the latter two devices being novel designs. The devices are used in protocols that include visual feedback to ascertain their effects on movement adaptation through the two feedback modalities.

General body discomfort increases over time during prolonged sitting and it is typically accepted that no single posture can be comfortably maintained for long periods. Despite this knowledge, workplace exposure to prolonged sitting is very common. Sedentary occupations that expose workers to prolonged sitting are associated with an increased risk of developing low back pain (LBP), disc degeneration and lumbar disc herniation. Given the prevalence of occupations with a large amount of seated work and the propensity for a dose-response relationship between sitting and LBP, refining our understanding of the biomechanics of the lumbar spine during sitting is important. Sitting imposes a flexed posture that, when held for a prolonged period of time, may cause detrimental effects on the tissues of the spine. While sitting is typically viewed as a sedentary and constrained task, several researchers have identified the importance of investigating movement during prolonged sitting. The studies in this thesis were designed to address the following two global questions: (1) How do the lumbar spine and pelvis move during sitting? (2) Can lumbar spine movement and postures explain LBP and injury associated with prolonged sitting? The first study (Study 1) examined static X-ray images of the lower lumbo-sacral spine in a range of standing and seated postures to measure the intervertebral joint angles that contribute to spine flexion. The main finding was that the lower lumbo-sacral joints approach their total range of motion in seated postures. This suggests that there could be increased loading of the passive tissues surrounding the lower lumbo-sacral intervertebral joints, contributing to low back pain and/or injury from prolonged sitting. Study 2 compared external spine angles measured using accelerometers from L3 to the sacrum with corresponding angles measured from X-ray images. While the external and internal angles did not match, the accelerometers were sensitive to changes in seated lumbar posture and were consistent with measurements made using similar technology in other studies. This study also provided an in-depth analysis of the current methods for data treatment and how these methods affect the outcomes. A further study (Study 3) employed videofluoroscopy to investigate the dynamic rotational kinematics of the intervertebral joints of the lumbo-sacral spine in a seated slouching motion in order to determine a sequence of vertebral motion. The pelvis did not initiate the slouching motion and a disordered sequence of vertebral rotation was observed at the initiation of the movement. Individuals performed the slouching movement using a number of different motion strategies that influenced the IVJ angles attained during the slouching motion. From the results of Study 1, it would appear as though the lowest lumbar intervertebral joint (L5/S1) contribute the most to lumbo-sacral flexion in upright sitting, as it is at approximately 60% of its end range in this posture. However, the results from Study 3 suggest that there is no consistent sequence of intervertebral joint rotation when flexing the spine from upright to slouched sitting. When moving from standing to sitting, lumbar spine flexion primarily occurs at the lowest joint (i.e. L5/S1); however, a disordered sequence of vertebral motion the different motion patterns observed may indicate that different joints approach their end range before the completion of the slouching movement. In order to understand the biomechanical factors associated with sitting induced low back pain, Study 4 examined the postural responses and pain scores of low back pain sufferers compared with asymptomatic individuals during prolonged seated work. The distinguishing factor between these two groups was their respective time-varying seated lumbar spine movement patterns. Low back pain sufferers moved more than asymptomatic individuals did during 90 minutes of seated work and they reported increased low back pain over time. Frequent shifts in lumbar spine posture could be a mechanism for redistributing the load to different tissues of the spine, particularly if some tissues are more vulnerable than others. However, increased movement did not completely eliminate pain in individuals with pre-existing LBP. The LBP sufferers’ seated spine movements increased in frequency and amplitude as time passed. It is likely that these movements became more difficult to properly control because LBP patients may lack proper lumbar spine postural control. The results of this study highlight the fact that short duration investigations of seated postures do not accurately represent the biological responses to prolonged exposure. Individuals with sitting-induced low back pain and those without pain differ in how they move during seated work and this will have different impacts on the tissues of the lumbar spine. A tissue-based rational for the detrimental effects on the spinal joint of prolonged sitting was examined in Study 5 using an in vitro spine model and simulated spine motion patterns documented in vivo from Study 4. The static protocol simulated 2 hours of sitting in one posture. The shift protocol simulated infrequent but large changes in posture, similar to the seated movements observed in a group of LBP sufferers. The fidget protocol replicated small, frequent movements about one posture, demonstrated by a group of asymptomatic individuals. Regardless of the amount of spine movement around one posture, all specimens lost a substantial amount of disc height. Furthermore, the passive range of motion of a joint changed substantially after 2 hours of simulated sitting. Specifically, there were step-like regions of reduced stiffness throughout the passive range of motion particularly around the adopted “seated flexion” angle. However, small movements around a posture (i.e. fidgeting) may mitigate the changes in the passive stiffness in around the seated flexion angle. The load transferred through the joint during the 2-hour test was varied either by changing postures (i.e. shifting) or by a potential creep mechanism (i.e. maintaining one static posture). Fidgeting appeared to reduce the variation of load carriage through the joint and may lead to a more uniform increase in stiffness across the entire passive range of motion. These changes in passive joint mechanics could have greater consequences for a low back pain population who may be more susceptible to abnormal muscular control and clinical instability. Nevertheless, the observed disc height loss and changes in joint mechanics may help explain the increased risk of developing disc herniation and degeneration if exposure to sitting is cumulative over many days, months and years. In summary, this work has highlighted that seated postures place the joints of the lumbar spine towards their end range of motion, which is considered to be risky for pain/injury in a number of tissue sources. In-depth analyses of both internal and external measurements of spine postures identified different seated motion patterns and self-selected seated postures that may increase the risk for developing LBP. The model of seated LBP/discomfort development used in this thesis provided evidence that large lumbar spine movements do not reduce pain in individuals with pre-existing LBP. Tissue-based evidence demonstrated that 2 hours of sitting substantially affects IVJ mechanics and may help explain the increased risk of developing disc herniation and degeneration if exposure to sitting is cumulative over many days, months and years. The information obtained from this thesis will help develop and refine interventions in the workplace to help reduce low back pain during seated work.

abstract: The development of advanced, anthropomorphic artificial hands aims to provide upper extremity amputees with improved functionality for activities of daily living. However, many state-of-the-art hands have a large number of degrees of freedom that can be challenging to control in an intuitive manner. Automated grip responses could be built into artificial hands in order to enhance grasp stability and reduce the cognitive burden on the user. To this end, three studies were conducted to understand how human hands respond, passively and actively, to unexpected perturbations of a grasped object along and about different axes relative to the hand. The first study investigated the effect of magnitude, direction, and axis of rotation on precision grip responses to unexpected rotational perturbations of a grasped object. A robust "catch-up response" (a rapid, pulse-like increase in grip force rate previously reported only for translational perturbations) was observed whose strength scaled with the axis of rotation. Using two haptic robots, we then investigated the effects of grip surface friction, axis, and direction of perturbation on precision grip responses for unexpected translational and rotational perturbations for three different hand-centric axes. A robust catch-up response was observed for all axes and directions for both translational and rotational perturbations. Grip surface friction had no effect on the stereotypical catch-up response. Finally, we characterized the passive properties of the precision grip-object system via robot-imposed impulse perturbations. The hand-centric axis associated with the greatest translational stiffness was different than that for rotational stiffness. This work expands our understanding of the passive and active features of precision grip, a hallmark of human dexterous manipulation. Biological insights such as these could be used to enhance the functionality of artificial hands and the quality of life for upper extremity amputees.
Dissertation/Thesis
Ph.D. Mechanical Engineering 2013