For sprint events longer than 100 m, more than half the race is run on the bend, yet bend sprinting has received little attention in biomechanics literature. The aim of this thesis was to understand the effect of the bend on maximal effort sprint performance and technique, using bend radii and surfaces typical of outdoor competition. Three empirical studies were undertaken with experienced bend sprinters. Initial 3D kinematics investigations revealed an approximately 5% velocity decrease on the bend compared to the straight. However, step characteristic changes contributing to this reduction were different for the left and right steps. For the left step there were significant decreases in step frequency (p < 0.05), due to increased ground contact time, which agreed with previously proposed theoretical models. For the right step, however, a significantly reduced flight time resulted in a significant reduction in step length (p < 0.05). Maintaining step length and an ‘active touchdown’ were closely related to an athlete’s ability to better maintain straight line velocity on the bend. Generally, velocity decreased as bend radius decreased, with mean differences of up to 2.3% between lanes 8 and 2. However, changes to athletes’ technique due to different lanes were not conclusive. Ground reaction forces revealed between-limb differences during bend sprinting. Furthermore, frontal plane forces were up to 2.6 times larger on the bend than on the straight. Overall, asymmetries were identified between left and right steps for several performance, technique and force variables, suggesting that bend sprinting induces different functional roles between left and right legs, with the left step contributing more to turning to remain on the bend trajectory. The differences in kinematic and kinetic characteristics between the bend and straight, and between-limb asymmetries mean that athletes should apply the principle of specificity to bend sprinting training and conditioning, without sacrificing straight line technique.

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A large number of studies have concentrated on golf swing biomechanics, ranging from planar rigid-link models to 3D kinematic analysis. A promising technique, instantaneous screw axis (ISA) theory, has not been covered in the literature and could provide a better true segment rotation approximation. The objectives of this study are to identify ISA location and orientation, as well as segment angular velocity, of the major body segments involved in the golf swing. For all subjects, it was found that the magnitude of maximum angular velocities increased from the most proximal segment (the pelvis) to the most distal segment (the left arm), in accordance with the summation of speeds principle. Furthermore, most subjects achieved their maximum angular velocities in the desired kinematic sequence, where the first maxima was achieved by the most proximal segment and followed by the more distal segments in the kinematic chain.

Existe um conceito difundido entre professores de educação física, fisioterapeutas e ortopedistas que o joelho não deve ser demasiadamente anteriorizado em relação à ponta do pé na direção ântero-posterior durante qualquer tipo de agachamento de modo a diminuir a carga mecânica imposta ao joelho. No entanto, são escassas as evidências quantitativas que corroboram este conceito. Este trabalho tem como objetivo estimar forças e torque na articulação do joelho em indivíduos saudáveis durante o exercício de agachamento livre com peso em dois modos diferentes de execução: a) joelho não ultrapassando a linha vertical que passa pelos dedos do pé; b) joelho ultrapassando essa linha vertical. Os sujeitos realizaram o agachamento com o pé direito sobre uma plataforma de força que mensurou os torques e forças de reação do solo. O membro inferior direito dos indivíduos (pé, perna e coxa) foram filmados com cinco câmeras digitais. Visando reconstruir o movimento dos segmentos, nós utilizamos a técnica de calibração do sistema anatômico (CAST), aumentando assim, a acurácia na reconstrução da posição tridimensional dos segmentos. O centro articular do quadril foi determinado pelo método rotacional e as forças e torques articulares internos líquidos foram determinados por dinâmica inversa. Os resultados obtidos mostram que o pico da carga mecânica no joelho, quando esse passa em média 11cm da linha do pé, é cerca de 31% maior na condição em que o joelho ultrapassa a linha do pé. Esses resultados implicam que não passar o joelho da linha do pé diminui a força de compressão patelofemoral, levando assim a uma menor solicitação mecânica nesta articulação. / There is a wide spread notion among health professionals that during a squat exercise the knee should not pass forward the forefoot region in order to not overload the knee joint. However, it seems there isn’t scientific literature to support or negate this concept. The goal of this paper is to investigate the effect of different foot-knee positions on the knee joint moment and on the patelofemoral force during squat, which was performed into two different ways: a) knee do not passing the forefoot region; b) knee passing the forefoot region. The subjects performed the squat exercise with the right foot on a force plate that measured the ground reaction force and moment components. The subject’s right leg (foot, shank, and thigh) and pelvis were filmed with five digital cameras. In order to reconstruct the segments’ movement, we used the Calibrated Anatomical System Technique (CAST), improving the accuracy on three-dimensional reconstruction of segment’s position. The hip center was determined by the rotational method and the internal net forces and torques were estimated by inverse dynamics. The results showed that during the condition were knee passed the forefoot region, the knee passed 11 cm on average, what resulted in a peak of mechanical load on the knee 30% higher in relation to the do not pass condition. Based on these results it is suggested that the knee should not pass the forefoot region during squatting in order to decrease the patelofemoral force.

Près d’un quart de la population mondiale présente au moins un signe de dysfonction de l’appareil manducateur, pour seulement 5 à 12% de prise en charge. Les différents composants de cet appareil fonctionnent en synergie et s’auto-influencent, ce qui entraîne des dysfonctions diverses, encore mal expliquées à ce jour. L’objectif de cette thèse est l’étude des mouvements mandibulaires pour la compréhension du fonctionnement de l’appareil manducateur, avec comme enjeu principal, la création d’un outil de diagnostic pour l’identification de dysfonctions. Pour cela, dans un premier temps, un protocole de mesures cinématiques, dont la précision et la répétabilité ont été caractérisées, a été proposé. Dans un second temps, les mesures cinématiques ont été réalisées sur 29 sujets asymptomatiques et 15 sujets avec dysfonctions mineures. Des mouvements élémentaires de la bouche en ouverture-fermeture, latéralité et propulsion ont été enregistrés. L’analyse des trajectoires des pôles condyliens dans différents plans anatomiques permet d’identifier des tendances générales mais met en évidence une grande variabilité inter-individuelle dans l’exécution des mouvements. L’étude des six mobilités de la mandibule complète cette information et démontre l’activation simultanée de translations et de rotations pour chacun des mouvements étudiés. Ceci constitue la première base de données de l’évolution des mobilités pour la mandibule humaine pour trois types de mouvements élémentaires. La comparaison de sujets présentant des dysfonctions mineures avec cette base de données montre que les mouvements de latéralité et de propulsion peuvent être des révélateurs de ces dysfonctions. Ces premiers résultats sont encourageants pour l’utilisation de l’analyse cinématique dans le cadre du diagnostic et du suivi de patients. / Nearly a quarter of the world's population has at least one sign of temporomandibular disorder, for only 5 to 12% of treatment. The different components of the masticatory system operate in synergy and self-influence, resulting in various dysfunctions which are still not well explained to date.The objective of this thesis is the study of the mandibular movements in order to understand the functioning of the masticatory system. The main challenge is the creation of a diagnostic tool for the identification of dysfunctions. To this end, a protocol of kinematic measurements was first proposed. Moreover, the precision and the repeatability of this protocol have been characterized. In a second step, the kinematic measurements were performed on 29 asymptomatic subjects and 15 subjects with minor dysfunctions. Basic movements of the mouth in opening-closing, lateral and propulsion were recorded. The analysis of condylar pathway in different anatomical planes makes it possible to identify general trends but shows a great interindividual variability in movements execution. The study of the six mobilities of the mandible completes this information and demonstrates the simultaneous activation of translations and rotations for each of the studied movements. This constitutes the first database of the evolution of mobilities for the human mandible for three types of basic movements. The comparison of subjects with minor dysfunctions with this database shows that the lateral and propulsion movements can be revealing of these dysfunctions. These first results are encouraging for the use of kinematic analysis in the diagnosis of temporomandibular disorders and patients monitoring.

Existe um conceito difundido entre professores de educação física, fisioterapeutas e ortopedistas que o joelho não deve ser demasiadamente anteriorizado em relação à ponta do pé na direção ântero-posterior durante qualquer tipo de agachamento de modo a diminuir a carga mecânica imposta ao joelho. No entanto, são escassas as evidências quantitativas que corroboram este conceito. Este trabalho tem como objetivo estimar forças e torque na articulação do joelho em indivíduos saudáveis durante o exercício de agachamento livre com peso em dois modos diferentes de execução: a) joelho não ultrapassando a linha vertical que passa pelos dedos do pé; b) joelho ultrapassando essa linha vertical. Os sujeitos realizaram o agachamento com o pé direito sobre uma plataforma de força que mensurou os torques e forças de reação do solo. O membro inferior direito dos indivíduos (pé, perna e coxa) foram filmados com cinco câmeras digitais. Visando reconstruir o movimento dos segmentos, nós utilizamos a técnica de calibração do sistema anatômico (CAST), aumentando assim, a acurácia na reconstrução da posição tridimensional dos segmentos. O centro articular do quadril foi determinado pelo método rotacional e as forças e torques articulares internos líquidos foram determinados por dinâmica inversa. Os resultados obtidos mostram que o pico da carga mecânica no joelho, quando esse passa em média 11cm da linha do pé, é cerca de 31% maior na condição em que o joelho ultrapassa a linha do pé. Esses resultados implicam que não passar o joelho da linha do pé diminui a força de compressão patelofemoral, levando assim a uma menor solicitação mecânica nesta articulação. / There is a wide spread notion among health professionals that during a squat exercise the knee should not pass forward the forefoot region in order to not overload the knee joint. However, it seems there isn’t scientific literature to support or negate this concept. The goal of this paper is to investigate the effect of different foot-knee positions on the knee joint moment and on the patelofemoral force during squat, which was performed into two different ways: a) knee do not passing the forefoot region; b) knee passing the forefoot region. The subjects performed the squat exercise with the right foot on a force plate that measured the ground reaction force and moment components. The subject’s right leg (foot, shank, and thigh) and pelvis were filmed with five digital cameras. In order to reconstruct the segments’ movement, we used the Calibrated Anatomical System Technique (CAST), improving the accuracy on three-dimensional reconstruction of segment’s position. The hip center was determined by the rotational method and the internal net forces and torques were estimated by inverse dynamics. The results showed that during the condition were knee passed the forefoot region, the knee passed 11 cm on average, what resulted in a peak of mechanical load on the knee 30% higher in relation to the do not pass condition. Based on these results it is suggested that the knee should not pass the forefoot region during squatting in order to decrease the patelofemoral force.

L’impact de la correction chirurgicale de la rupture du ligament croisé crânial (LCC) sur la cinématique 3D du grasset a peu été étudiée chez le chien. Plusieurs techniques tentent de restaurer la fonction normale du grasset suite à la rupture du LCC, mais les succès demeurent mitigés comme en témoignent le retour à une fonction suboptimale et la progression de l’arthrose. L’incapacité de ces techniques à restaurer la cinématique 3D pourrait être un élément clé expliquant ces succès suboptimaux. L’objectif de ce projet de recherche était d’évaluer l’impact d’une des techniques fréquemment utilisées, la stabilisation par suture latérale (SSL), sur la cinématique 3D du grasset. Dix membres pelviens provenant de grands chiens (25-40kg) ont été utilisés avec un montage préalablement validé simulant le trot. Trois situations ont été comparées : i) grasset sain, ii) grasset instable par transsection du LCC, et iii) grasset stabilisé par SSL. Pour chaque situation, la cinématique 3D était enregistrée durant 5 cycles dans le montage. Les courbes ont été analysées en utilisant un test statistique Wilcoxon signed rank test. La SSL a restauré la cinématique du grasset intact sain sur l’entièreté de la phase d’appui pour la translation crânio-caudale, médio-latérale, la flexion et l’abduction. Elle a restauré la translation proximo-distale sur 90% de la phase d’appui. La rotation interne a été limitée par la SSL, mais n’a pas été restaurée. Ces résultats montrent que cette technique chirurgicale reproduit une cinématique 3D globalement semblable à celle du grasset sain. La progression de l’arthrose rapportée suite à la stabilisation du grasset par SSL pourrait donc ne pas résulter d’une cinématique 3D anormale. / The impact of surgical correction of cranial cruciate ligament rupture (CCLR) on 3D kinematics has not been thoroughly evaluated in dogs. The success of current techniques remains limited, as illustrated by suboptimal weightbearing and progression of osteoarthritis. The inability to restore the stifle’s 3D kinematics might be a key element in understanding these suboptimal outcomes. The objective of this study was to evaluate the impact of lateral suture stabilization (LSS) on the 3D kinematics of the canine stifle joint. We hypothesized that LSS would not restore 3D kinematics in our model. Ten pelvic limbs collected from euthanized large dogs (25-40 kg) were tested with a previously validated apparatus that simulates trot. Three experimental conditions were compared: (a) intact stifle; (b) unstable stifle following cranial cruciate ligament transection (CCLt) and (c) CCLt stabilized by LSS. Three-dimensional kinematics were collected through 5 gait cycles and curves were analyzed using a Wilcoxon signed-rank test. LSS restored baseline kinematics for the entire stance phase for cranial and lateromedial translation, sagittal flexion, and abduction. It restored distraction over 90% of the stance phase. Internal rotation was limited, but not restored. This in vitro study had limitations, as it used a simplified model of stifle motion and weight-bearing. The results of this study demonstrate that LSS can restore physiologic 3D kinematics largely comparable to those of healthy stifles. Suboptimal outcome in patients following CCLR stabilization by LSS may therefore result from causes other than immediate postoperative abnormal 3D kinematics.