<p>In many occupational tasks, environmental constraints limit how close a worker can place their body to a desired element of the task. Although this provides an obstacle when performing the task, workplace obstructions can often be used by a worker to externally support their body by means of bracing. The purpose of this thesis was to identify how a worker’s posture would differ when the task must be performed with a constrained reach, compared to having the option to externally support against the thighs. At 4 different task hand Locations, subjects performed 6 exertions, comprised of 2 Loads (27.5 N and 55 N) and 3 Directions (Up, Down, and Pull). Subjects were able to choose if bracing would be used when performing the first 24 trial exertions. After the choice conditions had been collected, trials were performed again with a forced brace or unbraced. The most important finding of this study was that participants were twice as likely to brace when performing a task with a far reach. In addition, average brace forces were approximately 117 N for Up and Pull exertions, and were nearly half that (67 N) for Down exertions. Participants would brace at a lower height at low versus high locations. Flexing the trunk forward and twisting the right shoulder forward, combined with a more flexed task arm and reduced shoulder rotation, allowed participants to adopt a posture where their shoulder was closer to the point of exertion during braced exertions, thereby increasing their functional arm length.</p> / Master of Science in Kinesiology

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.

Tooth cusp radius of curvature (RoC) has been hypothesized to play an important role in food item breakdown, but has remained largely unstudied due to difficulties in measuring and modeling RoC in multicusped teeth. We tested these hypotheses using a parametric model of a four cusped, maxillary, bunodont molar in conjunction with finite element analysis. When our data failed to support existing hypotheses, we put forth and tested the Complex Cusp Hypothesis which states that, during brittle food items breakdown, an optimally shaped molar would be maximizing stresses in the food item while minimizing stresses in the enamel. After gaining support for this hypothesis, we tested the effects of relative food item size on optimal molar morphology and found that the optimal set of RoCs changed as relative food item size changed. However, all optimal morphologies were similar, having one dull cusp that produced high stresses in the food item and three cusps that acted to stabilize the food item. We then set out to measure tooth cusp RoC in several species of extant apes to determine if any of the predicted optimal morphologies existed in nature and whether tooth cusp RoC was correlated with diet. While the optimal morphologies were not found in apes, we did find that tooth cusp RoC was correlated with diet and folivores had duller cusps while frugivores had sharper cusps. We hypothesize that, because of wear patterns, tooth cusp RoC is not providing a mechanical advantage during food item breakdown but is instead causing the tooth to wear in a beneficial fashion. Next, we investigate two possible relationships between tooth cusp RoC and enamel thickness, as enamel thickness plays a significant role in the way a tooth wears, using CT scans from hundreds of unworn cusps. There was no relationship between the two variables, indicating that selection may be acting on both variables independently to create an optimally shaped tooth. Finally, we put forth a framework for testing the functional optimality in teeth that takes into account tooth strength, food item breakdown efficiency, and trapability (the ability to trap and stabilize a food item).

No description available.

INTRODUCTION: Tightness of the hip flexor muscle group may contribute to altered sagittal plane kinematics of the lumbo-pelvic-hip (LPH) complex during dynamic movements. Therefore, the purpose of this study is to analyze the effects of a three-week home-based stretching program on passive hip extension (PHE), as well as on active hip extension (AHE), anterior pelvic tilt (APT), and lumbar spine extension (LSE) when running. METHODS: Twenty healthy subjects with limited PHE underwent a 3D gait analysis both prior (PRE) and following (POST) a three-week static hip flexor stretching program. RESULTS: Following the stretching program, peak PHE increased significantly (P < 0.001), while no significant improvements were reported in AHE, APT, or LSE. In addition, no relationship was found between the change in PHE with either the change in AHE, APT, or LSE. Finally, a high relationship was observed between AHE and APT during running (r = 0.83, p < 0.001), and low relationships were observed between APT and LSE (r = -0.41, p = 0.08) and AHE and LSE (r = -0.34, p = 0.15). CONCLUSION: A three-week static stretching program of the hip flexor musculature resulted in an increase in PHE, but the sagittal plane kinematics of the LPH complex during running remained unchanged. The correlations observed between AHE, APT, and LSE suggest there is a kinematic relationship between the hip, pelvis, and spine.

Previously, it was reported that the morphological changes (pseudopod projection) that circulating neutrophils adopt due to cell activation raises peripheral vascular resistance by disrupting microvascular rheology. Studies utilized murine muscle preparations to link neutrophil pseudopod formation to cell activation and a viscous impact on hemodynamic resistance. But because of the complexity associated with the organization of the vasculature and microvasculature in tissues, it was unclear whether the effects of neutrophil activation on hemodynamic resistance were associated with the macro-/micro- circulation. This research describes an in vitro analysis using viscometry and microvascular network mimics (microporous membranes) to assess the rheological impact of pseudopods on capillary-like flow. Suspensions of neutrophil-like HL-60 promyelocytes (dHL60’s) and human neutrophils, stimulated with 10 nM fMLP were used, with/without hematocrit. Stimulation of dHL60s or human neutrophils with fMLP altered their flow behavior, which was detected as an increase in solution viscosity. Addition of hematocrit negated the effect of neutrophil activation on suspension viscosity. Moreover, cell activation increased the resistance of microporous membranes to flow of neutrophil suspensions with addition of hematocrit exacerbating this effect. Combined, the results of this study provided evidence that activated neutrophils influence microscale flow resistance via a rheological impact.

published_or_final_version / Orthopaedics and Traumatology / Master / Master of Philosophy

No description available.

No description available.

Introduction: Gait biomechanics are associated with knee osteoarthritis (OA) structural progression, but no studies have included: i) all three lower extremity joints, ii) non-frontal plane factors, iii) temporal loading patterns, and iv) progression from structural and symptomatic perspectives. This dissertation addressed gaps in our understanding of lower limb biomechanics and their implication for determining whether we have identified and are targeting the most effective biomechanical variables in the development and evaluation of conservative interventions to slow knee OA structural and symptom progression (progression to TKA). Methods: 54 patients with knee OA underwent baseline gait analysis. Three-dimensional hip, knee, and ankle angles and moments were calculated. Waveform characteristics were determined using Principal Component Analysis (PCA), and knee adduction moment (KAM) peak and impulse were calculated. At follow-up 5-8 years later, 26 patients reported undergoing total knee arthroplasty (TKA). Unpaired Student’s t-tests detected differences in baseline demographic and gait characteristics between TKA and no-TKA groups. Receiver operating curve analysis determined discriminative abilities of these differences. Stepwise discrimination analysis determined which multivariate combination best classified the TKA group. Logistic regression analysis determined the predictive ability of the multivariate model. Results: There were no baseline differences in clinical and spatiotemporal gait characteristics, but the TKA group showed significant gait biomechanical differences, including higher KAM magnitude (KAMPC1), less difference between early and mid-stance KAM (KAMPC2), higher KAM peak and impulse, reduced early stance knee flexion and late stance knee extension moments (KFMPC2), and reduced stance dorsiflexion moments (AFMPC4). The multivariate discriminant function with the highest classification rate (74.1%) combined KAMPC1, KFMPC2, and AFMPC4, with sensitivity of 84.6 and specificity of 71.4. A one-unit increase in the model score increased risk of progression to TKA six-fold. Conclusion: Higher KAMPC1 scores suggest higher overall loading during gait. Lower KFMPC2 and AFMPC4 scores suggest inability to unload the knee and therefore sustained loading. Interventions reducing overall load and altering patterns of loading (i.e. increase unloading) may reduce risk of progression to TKA. Future research should determine how components of the discriminant model can be altered conservatively, and what impact alterations have on the risk of progression to TKA.