Introduction: Claims that foot orthoses can resolve low-back pain are common in the marketing of these devices. The claims are based on the notion that wearing the orthoses will limit excess pronation at the subtalar joint thus reducing excessive internal tibial and femoral rotations. Excess leg rotations increase the anterior tilt of the pelvis and subsequently the degree of lumbar lordosis. Since lumbar lordosis has been suggested as a cause of low-back pain, it is speculated that foot orthoses could be used to treat and prevent pain to the low-back by reducing the forward curvature of the spine. This mechanical link between foot function and the low-back has not been investigated by experimental studies. Purpose: The purpose of this thesis was to investigate whether increased internal rotation of the femur induced an anterior tilt of the pelvis thus increasing the degree of lumbar lordosis and if external rotation induced a posterior pelvic tilt thus decreasing the degree of lumbar lordosis. Methods: In order to internally and externally rotate the femur, participants placed their feet in 18 different foot positions. Seven of these positions ranged from 15 degrees of foot eversion to 15 degrees of foot inversion and 11 positions ranged from 40 degrees of external foot rotation to 40 degrees of internal foot rotation. Six cameras surrounded the motion capture area and angles of pelvic tilt and lumbar lordosis were calculated. Results: Foot eversion and inversion did not have a statistically significant effect on pelvic tilt and lumbar lordosis. In-toeing had a statistically significant linear relationship with anterior pelvic tilt (R2=0.35, F1,131=69.79, p=0.00). Internally and externally rotating the feet had no effect on lumbar lordosis (R2=0.001, F1,153=0.09, p=0.77). Conclusion: Internally rotating the legs caused the pelvis to tilt anteriorly but only at extreme ranges of motion, much greater than what would normally be seen during gait. At which point, lumbar angles remained unaffected. This study does not dispute the effectiveness of foot orthoses to treat low-back pain but the results do not support the mechanical link proposed as the mechanism by which they work.

The purpose of this study was to biomechanically analyze the walking gait and knee motion of 19 female subjects. The gait and knee motions were studied under three conditions: (a) barefoot, (b) running shoes, and (c) high heeled shoes. Cinematographic and electrogoniometric techniques were used to obtain the data. An ANOVA and a Tukey post hoc statistical test (p < .05) were used to determine significance. Based on the findings of this study, significant decreases were found in: (a) the step length, (b) the horizontal distance from the center of gravity to the toe at heel strike, (c) the maximum flexion during the swing phase, (d) the range of valgus-varus motion during a step, and (e) the internal-external rotation during the swing phase in the high heeled shoe condition compared to the barefoot and running shoe conditions.

Debilitating valve disease necessitating valve replacement affects patients of all ages, all of whom would benefit from a tissue engineered heart valve with immunocompatibility, the ability of the valve to remodel in response to altered hemodynamics or patient growth, and physiologic mechanics. However, there may be age-specific requirements for such a valve. The overarching goal of this thesis was to characterize the extracellular matrix in developing, aging, and pathological mitral and aortic valves (MV, AV) in order to provide design criteria for an age-specific tissue engineered heart valve. The extracellular matrix plays a vital role in valve function; not only does it comprise the bulk of the valve tissue, but it determines the material properties of the valve, is integrally involved in biological signaling processes, and is altered in a number of valve pathologies. To this end, the composition, structure, and material properties of normal MV and AV were characterized with particular attention paid to valve heterogeneity and aging-related changes. Valves from disease states such as functional mitral regurgitation, dilated cardiomyopathy, iatrogenic valve wounds, calcific aortic valve disease, and myxomatous mitral valve disease were also analyzed to provide negative design criteria for a tissue engineered heart valve. Lastly, preliminary work was performed in developing a tissue engineered heart valve using poly(ethylene) glycol (PEG) hydrogels and valve cells of different ages. In sum, this body of work provides necessary design criteria for an age-specific tissue engineered heart valve, but in the process of analyzing various aspects of normal and diseased MV and AV, this thesis additionally provides insight into a variety of aspects of normal valve physiology, such as the relationship between valve composition and material properties and the mechanical environment, as well as insight into various valve diseases, such as the role of MV remodeling in functional mitral regurgitation and disease progression, with potential clinical implications for patients with these diseases.

Background: There is a high prevalence of injury and low back pain prevalence associated with professional drivers, including mobile police officers. In particular, the reduction in lumbar lordosis has been hypothesized as a contributing risk factor for injury during prolonged seated periods. Furthermore, the use of the mobile data terminal (MDT) and the protective equipment worn by officers creates a unique interface between the occupant and the car seat. Purpose: To evaluate a novel thoracic support that was designed to address the unique seated working demands of mobile police officers. Methods: Fourteen participants: 7 male (21.3 (1.9) years, 1.71 (0.06) m, 75.1 (9.3) kg) and 7 female (23.3 (4.4) years, 1.69 (0.06) m, 68.2 (7.7) kg) were recruited from a university student population. Participants attended two 120 minute driving simulations on separate days; using a standard Crown Victoria Interceptor seat and the same seat equipped with a retrofitted surface mounted thoracic support. Time-varying spine postures, seat pressure measures and perceived discomfort were measured. Results: The introduction of a thoracic support changed postures, reduced lower seat back interface pressures but did not reduce discomfort compared to a standard seat during a 2 hour exposure period. Average discomfort scores were low with all values below 10mm out of a possible 100mm for both seating conditions. Discomfort was found to have small increases over time in the neck and right thigh with the support, but mean values remained low (under 3mm). Lumbar angles became more flexed with the support compared to a standard seat. Posterior pelvic rotation was reduced in female participants while in males there was greater posterior pelvic rotation with the support. There was a reduction in interface pressures on the bottom half of the seat back, the area where the duty belt is in contact with the seat. Conclusions: The postural and seat interface information support further field evaluations using a retrofitted thoracic insert as an in-vehicle ergonomic intervention for police officers. Further investigations focussed on prolonged exposure to the intervention will guide future design iterations.

Juvenile red snapper are attracted to structure and settle onto low profile reefs, which serve as nursery grounds. Little is known about their life history during this time. However, recent studies from a shell bank in the NW Gulf of Mexico have shown higher growth rates for juveniles located on mud habitats adjacent to low profile reefs, perhaps due to varied prey availability and abundance. To further investigate the habitat needs of juvenile red snapper, individuals were collected from a low profile shell ridge (on-ridge) and adjacent mud areas (off-ridge) on Freeport Rocks, TX, and divided into three size classes (≤3.9 cm SL, 4.0-5.9 cm SL, ≥6 cm SL). Feeding morphology and kinematics were characterized and compared among size classes and between the two habitats. A dynamic jaw lever model was used to make predictions about feeding mechanics, and kinematic profiles obtained from high-speed videos of prey capture events validated the model’s predictive ability. Model output suggested an ontogenetic shift in feeding morphology from a juvenile feeding mode (more suction) to an adult feeding mode (more biting). Stomach contents revealed a concomitant shift in prey composition that coincided with the ontogenetic shift in feeding mode. The model also predicted that on-ridge juveniles would have faster jaw closing velocities compared to off-ridge juveniles, which had slower, stronger jaws. Analysis of prey capture events indicated that on-ridge juveniles demonstrated greater velocities and larger displacements of the jaws than off-ridge juveniles. Shape analysis was used to further investigate habitat effects on morphology. Off-ridge juveniles differed from on-ridge in possessing a deeper head and body. Results from model simulations, kinematic profiles, personal observations, and shape analysis all complement the conclusion that on-ridge juveniles exhibited more suction feeding behavior, whereas off-ridge juveniles used more biting behavior. Stomach contents demonstrated an early switch to piscivory in off-ridge juveniles compared to on-ridge juveniles, which may account for higher off-ridge growth rates. Habitat disparity, perhaps available prey composition, generated variations in juvenile feeding mechanics and consequently feeding behavior. This disparity may ultimately affect the growth rates and recruitment success of juvenile red snapper from different habitats.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (p. 100-111).

<p>The Neanderthal (<i>Homo neanderthalensis</i>) femur is distinct from that of recent modern humans (<i>Homo sapiens</i>). Broadly speaking, the Neanderthal femur is more &ldquo;robust&rdquo;, meaning that it appears to be biomechanically stronger, and it is more curved, which may enhance the predictability of the stresses and strains experienced by the bone. It has been hypothesized that the Neanderthal morphology is an adaptation to withstand elevated and repetitive loads associated with increased mobility. This study tests the mobility hypothesis using comparative and biomechanical methods. Specifically, this study sought to test the mobility hypothesis by a) determining whether or not a relationship exists between skeletal variables and day range (a surrogate for mobility) in living primates, and b) using finite element analysis to quantify differences in biomechanical strength between Neanderthals and modern humans while simulating loads associated with bipedal walking, traumatic loads, and stumbling. </p><p> The hypothesis that extant primates with longer day ranges exhibit more robust and more curved bones, used here as an indication of predictability of deformation, is rejected. The hypothesis that Neanderthal femora are as strong as or stronger than recent modern human femora is partially rejected. Under loading regimes simulating normal walking, it is unclear which femur is stronger. The human femur is stronger under simulated traumatic loads. The Neanderthal femur is stronger under loads simulating stumbling. The human femur is more predictable along the neck and at midshaft; the Neanderthal femur is more predictable along proximal and distal diaphyseal sections. The femoral neck is the weakest location on the modern human femur, whereas the distal lateral metaphysis is typically the weakest location on the Neanderthal femur. </p><p> Although a relationship between curvature and robusticity variables could not be confirmed using an extant primate sample, the unexpected results of the Neanderthal/human femur comparisons suggest that because regions of peak stress differ considerably between the species as a result of the differences in morphology, each may be adapted to the specific and typical demands imposed by their respective habitats and lifestyles. </p>

No description available.

Walking and running are essential tasks people take for granted every day. However, these are highly complex tasks that require significant neural control. This is complicated by the inherent redundancy of the nervous system and by physiological noise. Humans may adopt different control strategies to achieve different goals (environmental or task specific). More specifically, walking/running on a treadmill only requires that one not walk off the treadmill. Of the many possible strategies that can achieve this goal, humans attempt to maintain a constant speed from each stride to the next (Dingwell, John et al. 2010). However, how humans alter the stride-to-stride regulation of their gait when the task goals change (e.g., by maintaining stride length and/or time, during running, or during a predicted walk to run transition speed) has not yet been demonstrated. In the first two of three experiments conducted, healthy adults either walked or ran on a motorized treadmill at a comfortable speed under the following conditions: constant speed, constant speed with the stride length goal (targets on the treadmill), constant speed with the stride time goal (metronome), or constant speed with both stride length and stride time goals. In a third experiment, subjects walked and/or ran at a comfortable speed and also at their predicted theoretical walk to run transition speed. Goal functions derived from the task specifications yielded new variables that defined fluctuations either directly relevant to, or irrelevant to, achieving each goal. The magnitude of the variability, as well as the stride-to-stride temporal fluctuations in these variables, were calculated. During walking, subjects exploited different redundancy relationships in different ways to prioritize certain task goals (maintain stride speed) over others (maintain stride length or stride time) in each different context. In general, subjects made rapid corrections of those stride-to-stride deviations that were most directly relevant to the different task goals adopted in each walking condition. Thus, the central nervous system readily adapts to achieve multiple goals simultaneously. During running, subjects exhibited similar adaptations to walking, but over-corrected to prioritize maintaining stride speed even more strongly. This suggests that stepping control strategies adapt to the level of perceived risk. This purposeful adaptability of these stride-to-stride control strategies could be exploited to developing more effective rehabilitation interventions for patients with locomotor impairments. During the predicted walk-to-run speeds, subjects were able to largely exploit the redundancy within task goal, and effectively operated at “uncomfortable” speeds. These results suggest that the stride speed control is robust even with additional novel tasks and uncomfortable, abnormal speeds of locomotion. / text

published_or_final_version / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy