Theses and Dissertations from UMD

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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

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Identifying Plant and Feedback in Human Posture Control
(2010) Zhang, Yuanfen; Jeka, John; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Human upright bipedal stance is a classic example of a control system consisting of a plant (i.e., the physical body and its actuators) and feedback (i.e., neural control) operating continuously in a closed loop. Determining the mechanistic basis of behavior in a closed loop control system is problematic because experimental manipulations or deficits due to trauma/injury influence all parts of the loop. Moreover, experimental techniques to open the loop (e.g., isolate the plant) are not viable because bipedal upright stance is not possible without feedback. The goal of the proposed study is to use a technique called closed loop system identification (CLSI) to investigate properties of the plant and feedback separately. Human upright stance has typically been approximated as a single-joint inverted pendulum, simplifying not only the control of a multi-linked body but also how sensory information is processed relative to body dynamics. However, a recent study showed that a single-joint approximation is inadequate. Trunk and leg segments are in-phase at frequencies below 1 Hz of body sway and simultaneously anti-phase at frequencies above 1 Hz during quiet stance. My dissertation studies have investigated the coordination between the leg and trunk segments and how sensory information is processed relative to that coordination. For example, additional sensory information provided through visual or light touch information led to a change of the in-phase pattern but not the anti-phase pattern, indicating that the anti-phase pattern may not be neurally controlled, but more a function of biomechanical properties of a two-segment body. In a subsequent study, I probed whether an internal model of the body processes visual information relative to a single or double-linked body. The results suggested a simple control strategy that processes sensory information relative to a single-joint internal model providing further evidence that the anti-phase pattern is biomechanically driven. These studies suggest potential mechanisms but cannot rule out alternative hypotheses because the source of behavioral changes can be attributed to properties of the plant and/or feedback. Here I adopt the CLSI approach using perturbations to probe separate processes within the postural control loop. Mechanical perturbations introduce sway as an input to the feedback, which in turn generates muscle activity as an output. Visual perturbations elicit muscle activity (a motor command) as an input to the plant, which then triggers body sway as an output. Mappings of muscle activity to body sway and body sway to muscle activity are used to identify properties of the plant and feedback, respectively. The results suggest that feedback compensates for the low-pass properties of the plant, except at higher frequencies. An optimal control model minimizing the amount of muscle activation suggests that the mechanism underlying this lack of compensation may be due to an uncompensated time delay. These techniques have the potential for more precise identification of the source of deficits in the postural control loop, leading to improved rehabilitation techniques and treatment of balance deficits, which currently contributes to 40% of nursing home admissions and costs the US health care system over $20B per year.
Exercise and Depression: Causal Sequence Using Cross-Lagged Panel Correlation Analysis
(2009) Scott, Virginia Anne; Andrews, David L; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
This study sought to determine what kind of causal relationship, if any, exists between exercise and depression. A university student population (N = 178) was given the Godin Leisure Time Exercise Questionnaire and the Beck Depression Inventory-II at two time points separated by approximately one month. Cross-lagged panel correlation was used to make causal inferences based on the strength of the temporal relationships. After meeting the assumptions of synchronicity and stationarity, there was no significant difference between the cross-lagged correlations (ZPF = -0.4599, p = 0.65). Thus, no single causal pathway was dominant. While equal cross-lagged correlations can indicate spuriousness, it can also signify reciprocal causation. Exercise was not clearly the cause of reductions in depression, but neither was depression clearly the cause of physical inactivity. More complex causal pathways, such as reciprocal causation, warrant further investigation.
MULTI-DIGIT HUMAN PREHENSION
(2009) Park, Jaebum; Shim, Jae Kun; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The current dissertation addresses the central nervous system (CNS) strategies to solve kinetic redundancy in multi-digit static prehension under different geometries of hand-held objects and systematically varied mechanical constraints such as translation and rotation of the hand-held object. A series of experiments conducted for this dissertation tested the following hypotheses suggested in the current literatures for multi-digit human static prehension: Hierarchical organization hypothesis, principle of superposition hypothesis, proximity hypothesis, and mechanical advantage hypothesis. (1) Forces and moments produced by fingers during circular object prehension were grouped into two independent subsets: one subset related to grasping stability control and the other associated with rotational equilibrium control. This result supports the principle of superposition hypothesis. Individual fingers acted synergistically to compensate each other's errors. This result confirms the hierarchical organization hypothesis in circular object prehension. (2) During fixed object prehension of a rectangular object, the closer the non-task fingers positioned to the task finger, the greater the forces produced by the non-task fingers. However, during free object prehension, the non-task fingers with longer moment arms produced greater forces. The former and latter results support the proximity hypothesis and the mechanical advantage hypothesis, respectively. (3) The grasping stability control and rotational equilibrium control were decoupled during fixed object prehension as well as free object prehension. This result supports the principle of superposition hypothesis regardless of the mechanical constraints provided for these two prehension types. (4) During torque production, the fingers with longer moment arms produced greater forces when the fingers acted as agonists for the torque production. Therefore, the mechanical advantage hypothesis was supported for agonist fingers. (5) Coupling of thumb normal force and virtual finger normal force was not necessitated when horizontal translation of hand-held object was mechanically fixed. However, the coupling of two normal forces was always observed regardless of given translational constraints, and these two normal forces were independent to other mechanical variables such as tangential forces and moments. This result supports the principle of superposition hypothesis in static prehension under varied combinations of translational constraints.
Modeling Energy Transport in Porcine Skin
(2009) Keslin, Jeff Michael; di Marzo, Marino; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The ability to measure the burn depth in human skin is of great importance in identifying and successfully treating burn injuries. A non-invasive method for measuring this depth is described where a jet of cold air is impinged on the skin and the thermal and physiological response of the skin is observed. A computational model is developed to characterize the temperature response of the dead or burnt skin. This is validated using an experiment involving a jet impinging on a pig skin sample, with temperature measurements made by a non-invasive infrared thermocouple. This data can be used to create and compare a similar model with the inclusion of the physiological response that is present when the test is administered on live or partially burnt skin. Then a correlation may be developed that will predict the burn depth in the affected tissue.
Global Capitalism Meets Local Postcommunism: Tensions in Transition as Manifested through Physical Culture and the Female Body in Romania
(2008-11-21) Chin, Jessica; Andrews, David L.; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Nearly two decades after communism officially ended in Romania, the nation continues to struggle in its transition from state socialism to liberal democracy. The increased presence and influence of Western images, democratic ideals, and social ideologies produces a complex and unstable tension with persisting legacies of communism and socialist ideologies. This dissertation is a critical analysis of the ways in which various tensions are manifested within the changing physical culture in Romania, particularly through performative bodies and constructed spaces of leisure and physical activity. In addition, participation in sports and other physical activities related to fitness and health are examined to reveal disciplinary techniques that reinforce normalized constructions of gendered and classed bodies. Using a qualitative, multi-method approach, empirical data was primarily collected in gyms and fitness clubs of three major cities in Romania. Through a contextual, interpretive, and theoretically-informed analysis of the empirical findings, this project intends to expand upon and articulate theories of postcommunist transition, gender, and physical culture in the Eastern European context--opening new lines of inquiry that consider both the empowering and problematic implications of creating and negotiating new subject positions within postcommunist environments.
The influence of visfatin and visfatin gene polymorphisms on glucose and obesity-related variables and their responses to aerobic exercise training
(2008-08-12) McKenzie, Jennifer A; Hagberg, James M; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Adipokines, soluble factors produced by adipocytes, may help to connect diabetes and obesity; one such adipokine is visfatin. Previous research has linked visfatin and visfatin gene (PBEF1) polymorphisms with glucose and obesity-related conditions; however, less is known regarding visfatin's response to an aerobic exercise training intervention, and no one, to our knowledge, has examined whether polymorphic variation in the PBEF1 gene affects aerobic exercise training-induced changes in glucose and obesity-related variables. Thus, this retrospective study investigated whether 6 months of aerobic exercise training reduced plasma visfatin levels in individuals with impaired glucose tolerance (IGT) or normal glucose tolerance (NGT). In addition, we examined the influence of common PBEF1 gene polymorphisms (-4689 G>T, -1543 C>T, -1001 T>G, -948 G>T, and SER301SER) and haplotypes on glucose and obesity-related variables and their responses to aerobic exercise training. Following the completion of 6 weeks of dietary stabilization, 116 healthy, sedentary, middle-aged, Caucasian men and women underwent 6 months of aerobic exercise training. Glucose total area under the curve (AUC), insulin AUC, and insulin sensitivity were measured via oral glucose tolerance tests. Plasma visfatin was measured using an enzyme immunoassay in 67 of the participants (22 with IGT, 45 with NGT), and standard techniques were used to assess lipoprotein-lipid and body composition variables. Restriction fragment length polymorphism techniques and TaqMan assays were used to determine PBEF1 genotypes. We found that plasma visfatin levels were comparable in IGT and NGT individuals at baseline and increased similarly in both groups in response to aerobic exercise training. We also found associations at baseline between glucose and obesity-related variables and PBEF1 gene variants, with -4689, -1001, -948, and SER301SER variant allele groups and PBEF1 variant allele-containing haplotypes having higher insulin sensitivity. Last, PBEF1 genetic variation influenced the aerobic exercise training-induced change in glucose and obesity-related variables. Moreover, the -948 polymorphism, TCGTT haplotype, and TCGGT haplotype were associated with lipoprotein-lipid changes with training, and the SER301SER polymorphism influenced changes in BMI and body fat. Future studies need to address the functional significance of PBEF1 polymorphisms and haplotypes and clarify mechanisms connecting visfatin to glucose and obesity-related phenotypes.
Environmental Risk Factors, Health and the Labor Market Response of Households in the United States
(2008-08-04) Veronesi, Marcella; Alberini, Anna; Cropper, Maureen; Agricultural and Resource Economics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
In the first part of the dissertation, I estimate the effect of a married adult's specific health condition on his or her own labor market decisions (labor force participation, earnings, hourly wages, and hours of work) and his or her spouse's. I focus on cancer, stroke, ischemic heart disease, emphysema, chronic bronchitis, chronic obstructive pulmonary disease (COPD) and asthma. The effects differ by health condition and duration of the disease. Among married men who are working, having had emphysema for less than one year is enough to reduce the earnings of a man with college degree to those of a healthy man without high school diploma. My results also suggest that if a man has had cancer, his wife may have to compensate for the ensuing loss in household income by working more hours or entering the labor force. In the second part of the dissertation, I focus on the effect of children's asthma on mothers' labor force participation, on fathers' and mothers' labor supply, and on their hourly wages and weekly earnings. I compare these effects to those of a set of health conditions that includes deformities, congenital anomalies, heart problems, epilepsy and cancer. I find that single mothers with chronically ill children are the most affected group in terms of hours of work lost and reduction in earnings, and that fathers with an asthmatic child less than six years old work more hours per week. Then, I explore how mothers' labor force participation and hours of work affect days missed from school of a chronically ill child. I find that maternal employment is associated with a higher probability of a child missing school, and that this effect is the same for healthy children as for asthmatic children. In contrast, I find that if the mother works, then a child with deformities, congenital anomalies, heart problems, epilepsy or cancer is less likely to experience lost school days than if the mother does not work. I estimate the magnitude of these effects using data from the Medical Expenditure Panel Survey for U.S. households from 1996 to 2002.
Effect of long-term exercise on endothelial progenitor cells in healthy humans
(2008-04-24) Witkowski, Sarah; Hagberg, James M; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Endothelial progenitor cells (EPCs) are derived from the bone marrow and have been found to play a role in postnatal neovascularization and re-endothelialization. Reduced EPC number and function have been associated with death from cardiovascular diseases, CVD risk factors, and endothelial dysfunction. Oxidative stress, specifically, oxidized LDL (OxLDL) has been shown to decrease EPC number and function, and increase EPC senescence in vitro. Regular physical activity is related to lower rates of CVD; however the mechanisms underlying the benefits of exercise in the prevention of CVD are not fully clear. Exercise may improve the number, and function of EPCs while improving oxidative stress status. The primary purpose of this study was to compare CD34+/KDR+ EPC number, EPC clonogenic capacity, and senescence, in healthy men that have participated in greater than 20 years of moderate- to high-intensity exercise with low-active control subjects. To assess the effect of physical inactivity on these markers, a subset of exercisers (n=10) stopped exercising for 10 days after which, measures of EPC number, colony forming units, and senescence, endothelial function and oxidative stress were re-evaluated. Results showed that, CD34+/KDR+ cell number, CFU-Hill colonies, and EPC senescence were not statistically different between athlete and control groups. CD34+/KDR+ cell number was closely related to endothelial function. Specifically, the forearm blood flow response to reactive hyperemia was correlated with CD34+/KDR+ number in sedentary participants. Additionally, 5 athletes significantly decreased their CD34+/KDR+ number, which was related to a significant decline in endothelial function, indicating that regular physical activity is important for some athletes to maintain healthy endothelial function, perhaps through the maintenance of elevated number of circulating CD34+/KDR+ cells. CFU-Hill colony number was strongly correlated with hyperemic blood flow response in control participants and related to oxLDL independent of physical activity status. Athletes who participated in 10-days of exercise detraining demonstrated a significant decrease in EPC senescence, which was related to improved total antioxidant capacity. Overall, these results show that CD34+/KDR+ number is closely related to endothelial function. Moreover, the function of EPCs appears to be affected by oxidative stress and antioxidant availability.
The Experiences and Needs of Parents Whose Children Died Due to Degenerative Disabilities: A Qualitative Analysis
(2008-04-16) Stepanek, Jennifer Smith; Beckman, Paula J; Special Education; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Remarkable advancements in life-saving technology have led to prolonged survival rates for premature infants and young children who have experienced trauma, illnesses, or medical disabilities. However, this progress has also led to a concurrent increase in long-term morbidity, including chronic and degenerative health conditions that result in early death. Early interventionists, special educators, and other multidisciplinary professionals are subsequently working with a growing number of families who are facing the potential deaths of their children due to life-threatening disabilities. To support parents facing such loss, an understanding of their life experiences and support needs is essential. However, most research related to supporting grieving parents is based on samples drawn from self-help bereavement support groups which typically consist of parents whose children died as a result of catastrophic illnesses or trauma. Little is known about supporting parents whose children are diagnosed with life-threatening or degenerative disabilities. This qualitative inquiry explored the experiences and needs of 7 bereaved parents whose children died between the ages of 3 and 21 due to a degenerative neuromuscular disease. Four professionals also participated for triangulation in this national study. Narrative analysis was used to search for themes in the stories shared by participants. The themes that emerged for parent experiences include: abundant stress from dissonance, exhaustion, chronic changes, unanticipated shock, and profound grief; ongoing struggles for validation; and, the positive impact of formal and informal supports. The themes that emerged for parent needs include: hope, information, useful resources, helpful networks, healthy partnerships, choices, and validation. Finally, the themes that emerged for preferred supports during loss and bereavement include: professionals' awareness of and attention to parent experiences and needs throughout the child's lifespan; ongoing connections with providers and activities that were a part of the child's life; and, support options beyond traditional bereavement groups. The results are discussed with reference to previous and emerging theory and research in parental bereavement. Practical implications and future research are also discussed.
TNF Promoter Polymorphisms Associated with Skeletal Muscle Phenotypes in Humans
(2008-01-24) Liu, Dongmei; Roth, Stephen; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Skeletal muscle plays a central role in the overall health of individuals across all ages, and skeletal muscle phenotypes are influenced by both genetic and environmental factors. Tumor necrosis factor alpha (TNF-α), a key player in the innate and adaptive immune responses, has long been recognized as a potent catabolic factor mediating muscle wasting in various pathological conditions. Overproduction of TNF-α has been implicated in the etiology of age-associated muscle loss (sarcopenia). Individual capacities to produce TNF-α vary widely, which is partially attributable to gene sequence variations. The TNF-α coding gene, TNF, is highly polymorphic and single nucleotide polymorphisms (SNPs) in the promoter region of TNF have been implicated for the transcriptional regulation of TNF-α production, and associated with numerous inflammatory and infectious diseases. The purpose of the present study was to investigate the association of muscle phenotypes, including sarcopenia, with 5 TNF promoter SNPs, which are potentially of biological significance. A total of 1050 volunteers participating in the Baltimore Longitudinal Study of Aging (352 and 407 white women and men, 127 and 107 black women and men, and 30 and 27 non-white and non-black women and men) were genotyped for 5 TNF SNPs, and their regional and total body soft tissue masses and muscle strengths of upper and lower limbs were measured. Results indicated that TNF promoter SNPs are associated with muscle phenotypes in the participants: putative high TNF-α-producing alleles at positions -1031 and -863, individually or in combination in haplotype '1031C-863A-857C-308G-238G', are associated with lower muscle mass in males. These results suggest that genetic variation in the TNF locus may contribute to the inter-individual variation in muscle phenotypes, and imply that TNF-α may have a potential role in regulating body composition even in healthy people.

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