Browsing by Author "Davy, Kevin P."

Now showing 1 - 20 of 92
  • Thumbnail Image
    Advances in Nutrition Science and Integrative Physiology: Insights From Controlled Feeding Studies
    Davy, Kevin P.; Davy, Brenda M. (Frontiers, 2019-10-29)
    Nutrition science is a highly impactful but contentious area of biomedical science. Establishing cause and effect relationships between the nutrients and/or diets we consume and the avoidance of or risk of disease is extremely challenging. As such, evidence-based nutrition is best served by considering the totality of evidence across multiple study types including nutritional epidemiological studies, randomized controlled trials of behavioral interventions, and controlled feeding studies. The purpose of the present review is to provide an overview for those conducting research outside of clinical nutrition on how controlled feeding studies can be used to gain insight into integrative physiology/metabolism as well as to inform dietary guidelines. We discuss the rationale, basic elements, and complexities of conducting controlled feeding studies and provide examples of contributions of controlled feeding studies to advances in nutrition science and integrative physiology. Our goal is to provide a resource for those wishing to leverage the experimental advantage provided by controlled feeding studies in their own research programs.
  • Thumbnail Image
    Aging, Physical Activity, and Energy Intake Regulation
    Van Walleghen, Emily Lynn (Virginia Tech, 2006-07-31)
    More than seventy percent of Americans over the age of sixty are classified as overweight or obese, and the future incidence of these conditions is expected to rise. Although it is unclear why older adults are predisposed to weight gain, decreased total energy expenditure may contribute to positive energy balance. It is also possible that age-related impairments in energy intake regulation result in the inability to appropriately adjust food intake to meet energy requirements with advancing age. The purpose of these investigations was to determine the influence of age and habitual physical activity on acute regulation of energy intake. Secondary objectives were to determine if there are sex differences in energy intake regulation, and to determine if pre-meal water consumption decreases meal energy intake in young and older adults. To achieve these objectives, the ability to spontaneously adjust energy intake at a meal under "preloading" conditions in which a yogurt shake or water was consumed prior to the meal was determined. We hypothesized that older adults would demonstrate less accurate energy intake regulation than younger adults, but that energy intake dysregulation would be attenuated in physically active older adults. We also expected that young men would have higher accuracy of energy intake regulation compared to young women matched for dietary cognitive restraint and cardiorespiratory fitness, and that pre-meal water consumption would decrease meal energy intake in young and older adults. Our main finding was that energy intake regulation is significantly impaired in older compared to younger adults, and that habitual physical activity improves short-term, but not acute, energy intake regulation. We also found that young men demonstrate significantly higher accuracy of energy intake regulation compared to young women. Lastly, we determined that pre-meal water consumption significantly decreases meal energy intake in older, but not young, adults. Overall, these results indicate that acute energy intake regulation is less accurate with advancing age, but that regular physical activity improves short-term energy intake regulation. Additionally, sex appears to influence energy intake regulation, and water consumption is a potential strategy to reduce energy intake in older adults.
  • Thumbnail Image
    Aging, resistance training, and diabetes prevention
    Flack, Kyle D.; Davy, Kevin P.; Hulver, Matthew W.; Winett, Richard A.; Frisard, Madlyn I.; Davy, Brenda M. (2010-12-15)
    With the aging of the baby-boom generation and increases in life expectancy, the American population is growing older. Aging is associated with adverse changes in glucose tolerance and increased risk of diabetes; the increasing prevalence of diabetes among older adults suggests a clear need for effective diabetes prevention approaches for this population. The purpose of paper is to review what is known about changes in glucose tolerance with advancing age and the potential utility of resistance training (RT) as an intervention to prevent diabetes among middle-aged and older adults. Age-related factors contributing to glucose intolerance, which may be improved with RT, include improvements in insulin signaling defects, reductions in tumor necrosis factor-α, increases in adiponectin and insulin-like growth factor-1 concentrations, and reductions in total and abdominal visceral fat. Current RT recommendations and future areas for investigation are presented.
  • Thumbnail Image
    Angiotensin II receptor blockade and insulin sensitivity in overweight and obese adults with elevated blood pressure
    Marinik, Elaina (Virginia Tech, 2012-02-07)
    Currently, it is reported that ~65% and 34% of the U.S. population is overweight and obese, respectively. Obesity is a major risk factor for cardiovascular disease. Overweight and obese individuals are also at an increased risk of developing hypertension. Whole-body insulin sensitivity is reduced in obesity, resulting in insulin resistance and increased risk of type 2 diabetes. One possible mechanism contributing to insulin resistance in obesity hypertension is renin-angiotensin system (RAS) overactivation. The RAS exhibits vasocontricting and sodium-retaining properties, yet in vivo and in vitro animal experiments suggest impairment of whole-body insulin sensitivity with increased angiotensin II (Ang II) exposure. Furthermore, evidence from clinical studies indicates Ang II receptor blockers (ARBs) may reduce the incidence of new-onset diabetes compared to other antihypertensive agents in at-risk hypertensive patients. However, it is unclear if whole-body insulin sensitivity is improved with Ang II receptor blockade in humans. Thus, we tested the hypothesis that 8-week Ang II receptor blockade with olmesartan would improve whole-body insulin sensitivity in overweight and obese individuals with elevated blood pressure (BP). Olmesartan was selected for the present study because it is devoid of partial PPARγ agonist activity. To test our hypothesis, intravenous glucose tolerance tests were performed to measure insulin sensitivity before and after control and ARB treatment in a randomized crossover manner. Because skeletal muscle tissue accounts for ~75-90% of insulin-stimulated glucose uptake, a secondary exploratory aim was to examine skeletal muscle inflammatory and collagen response in relation to insulin sensitivity during ARB treatment. No baseline differences were observed between treatments (P>0.05). Both systolic (-11.7 mmHg; P=0.008) and diastolic (-12.1 mmHg; P=0.000) BP were reduced with ARB treatment. Insulin sensitivity was not different between treatments (P>0.05). No correlates of insulin sensitivity were identified. In addition, skeletal muscle inflammatory and collagen gene expression did not change from pre- to post-ARB treatment (P>0.05). Our findings suggest that short-term RAS blockade in overweight and obese adults with elevated BP does not improve whole-body insulin sensitivity, despite a significant BP reduction. Further studies are needed to clarify the role of individual RAS blockers on insulin sensitivity during RAS inhibition in obesity hypertension.
  • Thumbnail Image
    Are the Initiation and Maintenance of a Resistance Training Program Associated with Changes to Dietary Intake and Non-Resistance Training Physical Activity in Adults with Prediabetes?
    Halliday, Tanya M. (Virginia Tech, 2016-05-02)
    Prediabetes is associated with an elevated risk for developing type 2 diabetes (T2DM) and associated cardiovascular complications. Lifestyle factors such as physical activity (PA) and dietary intake are strongly implicated in the development of metabolic disease, yet few Americans meet PA and dietary recommendations. Middle-aged and older adults are at increased risk for developing prediabetes and T2DM due to age-related muscle loss, increased fat mass, and alterations in glucose handling. In addition, this segment of the population is least likely to meet PA guidelines, particularly the resistance training (RT) recommendation of completing a whole body routine 2x/week. Ideally, individuals would alter their lifestyle in order to meet PA guidelines and habitually consume a healthy diet, to decrease disease risk. However, behavior change is difficult and optimal strategies to promote and maintain changes have yet to be determined. Furthermore, behavior change interventions tend to be time-, cost-, and resource-intensive, limiting the ability for efficacious programs to be translated into community settings and broadly disseminated. Evidence suggests that health-related behaviors, particularly diet and exercise habits, tend to cluster together. Thus, intervening on one behavior (e.g. PA) may elicit a spillover effect, promoting alterations in other behaviors (e.g. diet), though findings to date are conflicting. The purpose of this dissertation was to determine if participation in a social cognitive theory-based RT program targeting the initiation and maintenance of RT exerts a spillover effect and is associated with alterations in dietary intake and/or non-RT PA in a population at risk for T2DM. Data from the 15-month Resist Diabetes study was analyzed to evaluate this possibility. Sedentary, overweight/obese (BMI 25-39.9 kg/m2 ), middle-aged and older (50 -69 years) adults with prediabetes (impaired fasting glucose and/or impaired glucose tolerance) completed a 3 month initiation phase where they RT 2x/week in a lab-gym with an ACSM-certified personal trainer. Participants then completed a 6-month faded contact maintenance phase, and a 6-month no-contact phase during which they were to continue RT on their own in a public facility. No advice or encouragement was given to participants to alter dietary intake or non-RT PA habits. At baseline, and months 3, 9, and 15, three non-consecutive 24-hour diet recalls were collected to evaluate dietary intake and quality, the Aerobics Institute Longitudinal Study Questionnaire was completed to evaluate non-RT PA, and body mass, body composition, and strength (3 repetition maximum on leg and chest press) were measured. At months 3, 9, and 15 social cognitive theory (SCT) constructs were assessed with a RT Health Beliefs Questionnaire. In the first study, dietary intake was assessed at baseline and after 3 months of RT. Using paired sample t-tests, reductions in intake of energy (1914 ± 40 kcal vs. 1834 ± 427 kcal, p = 0.010), carbohydrate (211.6 ± 4.9 g vs. 201.7 ± 5.2 g, p = 0.015), total sugar (87.4 ± 2.7 g vs. 81.5 ± 3.1 g, p = 0.030), glycemic load (113.4 ± 3.0 vs. 108.1 ±3.2, p= 0.031), fruits and vegetables (4.6±0.2 servings vs. 4.1±0.2 servings, p= 0.018), and sweets and desserts (1.1 ± 0.07 servings vs. 0.89 ± 0.07 servings, p = 0.023) were detected from baseline to month 3. No changes in other dietary intake variables were observed. These findings supported additional investigation in this area. The second study assessed changes in overall diet quality (Healthy Eating Index [HEI]-2010 scores) and non-RT PA over the initiation, maintenance, and no-contact phases using mixed effects models. Demographic, physiological, and psychosocial factors that may predict alterations to diet quality and non-RT PA were also explored. Energy and carbohydrate intake decreased with RT (β= -87.9, p=.015 and β= -16.3, p<.001, respectively). No change in overall dietary quality (HEI-2010 score: β= -0.13, p=.722) occurred, but alterations in HEI-2010 sub-scores were detected. Maintenance of RT was accompanied by an increase in MET-min/week of total non-RT PA (β=153.5, p=0.01), which was predicted by increased self-regulation for RT (β=78.1, p=0.03). RT may be a gateway behavior leading to improvements in other health-related behaviors among adults with prediabetes. These results support the use of singlecomponent vs. multi-component interventions. This may have broad translational potential for the development of time-, resource-, and cost-efficient lifestyle interventions which can improve multiple health-related behaviors and decrease disease risk.
  • Thumbnail Image
    Are There Sex Differences in Behavioral Predictors of Successful Weight Loss Maintenance?
    Baugh, Mary Elizabeth (Virginia Tech, 2013-10-16)
    Current literature emphasizes poor long-term weight loss maintenance (WTLM) outcomes, and the need for inexpensive, practical solutions for effective WTLM is evident. Individuals successful at WTLM utilize similar behaviors but in varying amounts and combinations, seemingly choosing behaviors that best fit their preferences. Researchers have attempted to identify characteristics of individuals that may predict successful WTLM in order to develop flexible WTLM treatments based on individuals' lifestyle and preferences. The purpose of this analysis was to examine sex differences in WTLM outcomes and to identify potential behaviors related to WTLM success. In a 12-month study targeting WTLM, weight-reduced middle-aged and older men and women (n=39) were assigned behavioral goals for body weight, fruit and vegetable intake, water consumption, and physical activity and were asked to daily self-monitor body weight and these behaviors. Sex difference in clinically significant WL ≥5% WL) at 12 months was determined. A growth curve model assessed interactions of sex and WTLM predictors, and a crisp set qualitative comparative analysis (QCA) characterized individuals' weight changes and behaviors. No sex difference was found in clinically significant WL or in the interaction of sex and behaviors on weight change; however, QCA evidence suggests men and women may approach WTLM with different behaviors. Additionally, QCA findings suggest weight change in the first 3 months of WTLM may determine success at 12-months. WTLM treatments should provide more intensive support during the transition period from WL to WTLM. Future research in predictors of WTLM, particularly within the context of sex, is essential.
  • Thumbnail Image
    Arterial Destiffening with Weight Loss in Overweight and Obese Middle-Aged and Older Adults
    Dengo Flores, Ana Laura (Virginia Tech, 2010-06-15)
    Cardiovascular diseases (CVD) are the leading cause of mortality in the United States. Aging is the major risk factor for CVD development, which is independently predicted by arterial stiffness (AS). Arterial stiffening is closely related to age-related arterial structural/functional changes and obesity. Therefore, obese middle-aged and older adults are considered a high CVD risk population. In light of the current obesity epidemic and the projected growth of the older population, there is an overwhelming need to determine if weight loss (WL) may reduce AS (CVD risk) in this population. Thus, we hypothesized that WL via a hypocaloric diet-alone would reduce AS in overweight and obese middle-aged and older adults. To test our hypothesis, baseline assessment of anthropometrics, blood pressure and AS was conducted, and subjects were randomized to a 12-week WL intervention or a control group. Arterial stiffness was measured using applanation tonometry to estimate carotid-femoral artery pulse wave velocity (C-F PWV), and with high-resolution ultrasonography of the carotid artery (β-SI). There were no baseline differences between groups in our variables of interest. Consistent with our hypothesis, both measures of AS were significantly reduced (C-F PWV= -16% and β-SI= -12%, P<0.05) with WL (-8%, P<0.05). Weight loss also resulted in significantly decreased blood pressure, total body and abdominal fat. No such changes were observed in the control group. Pooled correlation analysis suggests that the magnitude of change in C-F PWV was not associated with changes in systolic, diastolic or mean blood pressure. We further hypothesized that reductions in AS, if observed, would be associated with the magnitude of reduction in total body or abdominal adiposity. Concordant with our hypothesis, the reductions in C-F PWV were significantly associated with total and abdominal fat. However, linear regression analysis indicate that neither total body nor abdominal body fat were capable of independently predicting reductions in C-F PWV. Our findings suggest that moderate WL in overweight and obese middle-aged and older adults is an efficacious treatment strategy for reducing AS. Further studies are needed to determine if the improvements in arterial compliance would be sustained with long-term WL maintenance.
  • Thumbnail Image
    Assessing the Cardiovagal Baroreflex
    Behnam, Abrahm John (Virginia Tech, 2007-02-02)
    Abrupt decreases and increases in systolic arterial blood pressure produce baroreflex mediated shortening and lengthening, respectively, of the R-R interval. This phenomenon, otherwise known as the cardivagal baroreflex, is best described by the sigmoid relationship between R-R interval length and systolic blood pressure. The linear portion of this relationship is used to derive the slope or gain of the cardiovagal baroreflex. Importantly, lower levels of cardiovagal baroreflex have been associated with poor orthostatic tolerance and an increased cardiovascular disease-related mortality. The most commonly used and accepted technique to assess cardiovagal barorelex gain is the modified Oxford techinique. Bolus injections of sodium nitroprusside followed by phenylephrine HCL are used to decrease and raise blood pressure ~15 mmHg, respectively. The baroreflex control of the cardiac vagal outflow can then be assessed by the relation of the R-R interval to systolic blood pressure. However, the modified Oxford technique does not always reveal the nonlinear nature of baroreflex relations. The reasons for this has been unclear. Thus, analysis of baroreflex gain when nonlinearities are not revealed is problematic. Five classifications of baroreflex trials have been identified: acceptable, threshold-heavy, saturation-heavy, linear-heavy, and random trials. A new method of gain estimation was developed that combines the strengths of the current methods of gain estimation with the knowledge of the classifications of baroreflex trials. Using this method, cardiovagal baroreflex gain assessment can be maximized if threshold-heavy, saturation-heavy, and random trials are filtered out of the analysis and the manual method is used to estimate gain on the remaining trials. In addition, a link seems to exist between the variability of delta and the variability in baroreflex gain between different subjects.
  • Thumbnail Image
    The Association between Non-Nutritive Sweetener Intake and Metabolic Syndrome in Adults
    Hess, Erica Lynn (Virginia Tech, 2017-06-06)
    Non-nutritive sweeteners (NNS) have been used to replace added sugars in foods/beverages. Research related to NNS consumption and metabolic syndrome (MetS) is of great importance as NNS are often used by individuals who are looking to improve their health. The objectives of this investigation were to determine whether an association between NNS consumption (total and individual types) and MetS exists, and if any of the five risk factors for MetS were more significantly impacted by NNS consumption. Four NNS were included in this study: saccharin, sucralose, aspartame, and acesulfame potassium. Adult participants (n = 125) from Southwest Virginia were recruited for a cross-sectional investigation. Demographics, three 24-hour dietary recalls, and values for MetS (blood pressure, waist circumference, and glucose, triglyceride, and HDL levels) were collected. Statistical analyses included descriptives and multiple linear regressions models. Of the 125 participants, 63 were classified as NNS consumers and 18 met the criteria for MetS. There was a significant positive relationship between MetS and total NNS consumption (p=0.007) and MetS and aspartame (p=0.012). When looking at individual MetS risk factors, waist circumference, triglyceride and glucose values were significantly positively associated with NNS consumption (p≤0.001) and aspartame, sucralose, and saccharin (all p≤0.027). Some limitations to current NNS research were addressed, such as, examining associations between individual NNS types and not using diet soda as a proxy for NNS consumption. More research is needed to address the bias of self-reported data and the lack of randomized controlled trials to inferentially test the impact of NNS consumption.
  • Thumbnail Image
    Athlete Monitoring in American Collegiate Football
    Lewis, Marc Theron (Virginia Tech, 2021-03-17)
    American football is one of the most popular sports in the United States. However, in comparison to other mainstream sports such as soccer and rugby, there is limited literature using scientific principles and theory to examine the most appropriate ways to monitor the sport. This serves as a barrier to American football practitioners in their development and implementation of evidence-based sport preparation programs. Therefore, the primary aim of this line of research (i.e., dissertation) is to illustrate the efficacy of commonly used athlete monitoring tools within the sport of American collegiate football, while proposing a systematic framework to guide the development of an athlete monitoring program. This aim was achieved through a series of studies with the following objectives: 1) to quantify the physical demands of American collegiate football practice by creating physiological movement profiles through the use of integrated microtechnology metrics and heart rate indices, 2) to determine the positional differences in the physical practice demands of American collegiate football athletes, 3) to examine which integrated microtechnology metrics might be used to most efficiently monitor the training load of American collegiate football athletes, 4) to demonstrate the suitability of using the countermovement jump (CMJ) to assess training adaptations in American collegiate football athletes through examining weekly changes in CMJ performance over the course of two 4-week periodized training blocks (8 weeks total), and 5) to examine the effect of acute fatigue on CMJ performance in American football athletes. The first study from this line of research quantified the physical demands of American collegiate football by position groups and found significant differences in both running based and non-running based training load metrics. In addition, the first study utilized a principal component analysis to determine 5 'principal' components that explain approximately 81% of the variance within the data. The second study utilized a univariate analysis and found significant changes in CMJ performance due the effect of time with significant improvements in CMJ 'strategy' variables over the training period. Finally, the third study used effects sizes to illustrate a larger magnitude of change in CMJ 'strategy' variables than CMJ 'output' variables due to effect of acute fatigue. Results from studies 2 and 3 suggest the importance of monitoring CMJ strategy variables when monitoring training adaptations and fatigue in American collegiate football athletes. This line of research provides practitioners with a systematic framework through which they can develop and implement evidence-based sport preparation programs within their own organizational context. In addition, this line of research provides practitioners with recommendations for which metrics to monitor when tracking training load in American collegiate football using integrated microtechnology. Finally, this line of research demonstrates how to assess training adaptations and fatigue using the CMJ within the sport of American collegiate football, while providing an empirical base through which the selection of CMJ variables can take place. Collectively, this line of research uses scientific principles and theory to extend the current literature in American collegiate football, while providing practitioners with a guide to athlete monitoring within the sport.
  • Thumbnail Image
    Behavioral Inhibition/Activation and Autonomic Control of the Heart: Extending the Autonomic Flexibility Model
    Christie, Israel C. (Virginia Tech, 2005-05-09)
    The autonomic flexibility model has proven to be a useful theoretical tool relating reductions in physiological variability found to accompany anxiety and concomitant reductions in behavioral (e.g., cognitive and emotional) flexibility. The present study aimed to extend the autonomic flexibility model through the inclusion of individual differences in the sensitivity of the independent motivational systems presumed to underlie anxiety and impulsivity, namely the behavioral inhibition and activation systems (BIS/BAS; Gray, 1994). Contrary to the predicted inverse relationship between BIS sensitivity and measures of physiological variability, findings suggest BAS sensitivity is associated with increased trait-like vagally mediated heart rate variability across diverse tasks as well as greater flexibility in responding within tasks. Numerous BIS*BAS interactions emerged as significant predictors of trait reactivity. Results are discussed in terms of the interface between (1) mesolimbic dopaminergic projections to the nucleus accumbens and (2) the network of central nervous system structures believed to play a large role in controlling peripheral physiology.
  • Thumbnail Image
    Cellular Reprogramming in Skeletal Muscle after Repeated Exposures to Endotoxin
    Denko, Laura Michelle (Virginia Tech, 2012-06-21)
    Obesity-related metabolic derangements have been linked to toll-like receptor 4 (TLR4), an innate immune system receptor, due to its role in proinflammatory pathways. Lipopolysaccharide (LPS), a gram-negative bacteria cell wall component, is the ligand for TLR4, and has been shown to be elevated in states of metabolic disease. Heightened levels of circulating endotoxin is termed metabolic endotoxemia and has been linked to systemic inflammation which is associated with obesity, type 2 diabetes mellitus (T2DM), and cardiovascular disease (CVD). Immune cells exhibit a protective ability to develop endotoxin tolerance. The objective of this study was to determine if endotoxin tolerance exists in skeletal muscle cells, and if a condition that mimics a state of over nutrition, such as elevated levels of fatty acids, affect this tolerance. To this end, L6 skeletal muscle cells were treated with low (50 pg/mL)- and high (500 ng/mL)-doses of LPS, with and without the presence of free fatty acids (FFAs). Tolerance was assessed by measuring: 1) changes in mRNA expression of interleukin-6 (IL-6) and monocyte chemoattractant-1 (MCP-1) as markers of a pro-inflammatory response; and 2) mRNA levels of peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC1-°) and mitochondrial oxidative capacity via an XF24 Flux Analyzer (Seahorse Bioscience) as measures of the metabolic response. Tolerance to LPS was observed in response to low- and high-doses with MCP-1 mRNA transcription but not IL-6. Changes in PGC1-° and mitochondrial OCR exhibited a tolerant effect in response to the high dose of LPS but not the low dose. The addition of free fatty acids to LPS treatments did not prevent the tolerant effects under any conditions. In conclusion, LPS tolerance exists in skeletal muscle cells but appears to differ depending on pro-inflammatory target and LPS concentration. Additionally, fatty acids, in the current model, have no effect on LPS tolerance.
  • Thumbnail Image
    Characterization of an in vitro exercise model and the effects of a metabolic endotoxemia on skeletal muscle adaptation to electric pulse stimulation
    Harvey, Mordecai Micah (Virginia Tech, 2017-06-20)
    The prevalence of obesity and type II diabetes is increasing. Although exercise is widely accepted for prevention and treatment, evidence of resistance to exercise in patients with these diseases is also mounting. Muscle contraction during exercise stimulate cellular responses important for adaptation. These responses include the release of myokines and the subsequent increase in substrate metabolism. This study aimed to define a culture model for simulating exercise in human primary skeletal muscle cells. We hypothesized that chronic electric pulse stimulation (EPS) of human myotubes in vitro would emulate cellular and molecular responses to exercise observed in vivo. To define this model, we applied EPS to human myotubes for varied lengths of time and measured interleukin-6 (Il-6), peroxisome proliferator-activated receptor gamma coactivator 1- (PGC1-), superoxide dismutase 2 (SOD2), substrate metabolism, metabolic enzyme activity, heat stress markers, and pH. To recreate the inflammatory milieu observed in metabolic disease states we treated the myotubes with a low dose of 20 EU lipopolysaccharide (LPS). Following the 24-hour stimulation we observed significant increases in transcription of Il-6, PGC1-, and SOD2. Basal glucose and fatty acid oxidation were also markedly increased in the cells after EPS. Cells treated with LPS elicited a blunted transcriptional, metabolic, and enzymatic response to EPS. These findings suggest that EPS is a viable model for simulating the effects of exercise. Our observations also indicate that an inflammatory environment could play a role in interfering with the adaptations to exercise.
  • Thumbnail Image
    Comparison of assessment techniques: plasma lipid and lipoproteins related to the metabolic syndrome
    Davy, Brenda M.; Davy, Kevin P. (Biomed Central, 2006-01-31)
    Background The purpose of this investigation was to determine the influence of analytical method on reported concentrations of plasma lipids and lipoproteins, and to determine if there are clinical implications of any potential differences on identification of the metabolic syndrome dyslipidemia, CVD risk stratification and classification of LDL subclass phenotype. Results Plasma triglyceride (TG) concentrations were 1.09 ± 0.06 and 1.17 ± 0.06 mmol/L and plasma high density lipoprotein cholesterol (HDL-C) concentrations were 1.09 ± 0.03 vs 1.19 ± 0.03 mmol/L (both p < 0.05) from 113 duplicate samples sent to two laboratories utilizing different lipid and lipoprotein analytical methods (LABS 1 and 2, respectively). Plasma total cholesterol and low-density lipoprotein cholesterol (LDL-C) concentrations were also significantly different between laboratories. Spearman rho correlations indicate excellent agreement of TG and HDL-C determined by the two laboratories (r = 0.96, TG; r = 0.91, HDL-C, both p < 0.001). Eleven vs. 14 individuals met the TG criteria and 70 vs. 48 met HDL-C metabolic syndrome criteria with LAB 1 and 2, respectively. Apoprotein B concentration (LAB 1) and LDL particle number (LAB 2) were highly correlated. (r = 0.92, P < 0.01). LAB 2 characterized more individuals as LDL pattern B phenotype, as compared to LAB 1 (30 vs. 14%, P < 0.05). Conclusion Different plasma lipid and lipoprotein analytical techniques yield results which are highly correlated, yet significantly different, which suggests a consistent measurement difference. This difference has clinical implications, in that the proportion of individuals identified as meeting the metabolic syndrome dyslipidemia criteria, "at risk" based upon apo B or LDL particle number, and the LDL pattern B phenotype will differ based upon choice of analytical method.
  • Thumbnail Image
    Contractile Performance and Energy Utilization of Skeletal Muscle; Creatine Kinase and Acto-myosin ATPase
    Melnyk, Jason Alexander (Virginia Tech, 2009-01-23)
    Creatine kinase (CK) primarily serves as an energy buffer assisting in regulating ATP homeostasis through synthesis of ATP from ADP and phosphocreatine (PCr). This enzyme is bound in the sarcomere near sites of ATP consumption via acto-myosin ATPase (A‧M‧ATPase) and research in cardiac muscle has found that PCr can alter contractile performance (maximal isometric force and Ca²⁺ sensitivity). Based on this evidence, CK and A‧M‧ATPase may be coupled in skeletal muscle. Therefore the purpose of this investigation was to determine the influence of the CK system on contractile performance and energy utilization in skeletal muscle. When skinned fibers (membrane removed) were provided a limited supply of [ATP] (0.1 mM), this resulted in increased Ca²⁺ sensitivity. The addition of PCr to low ATP solutions restored Ca²⁺ sensitivity and allowed normal isometric force generation across a range of [Ca²⁺] via ATP synthesis by CK. This was also possible with only CK reaction substrates (ADP, PCr) in the absence of ATP. Based on these findings, endogenous CK activity in glycerol skinned skeletal muscle fibers is sufficient to permit normal function of the contractile apparatus. Energy utilization was studied by indirect assessment of ADP production. Decreased net ADP production as measured by NADH fluorescence revealed endogenous CK was able to convert ADP produced by A‧M‧ATPase to ATP in skeletal muscle across a range of both [Ca²⁺] and [ATP]. This was confirmed directly via high-performance liquid chromatography measurements of ATP and ADP by showing that skinned skeletal muscle bundles have sufficient endogenous CK activity to produce ATP from substrates (ADP, PCr) and the ability to maintain low [ADP] in the presence of PCr. This study adds to the evidence for specific compartmentation of CK near sites of ATP utilization and contributes to the body of knowledge on contractile performance in skinned skeletal muscle fibers. By showing how changing demands on skeletal muscle (through increased Ca²⁺) alters force production and Ca²⁺ sensitivity, these findings lend support for the importance of endogenous CK as a pathway of ATP regeneration in skeletal muscle.
  • Thumbnail Image
    Dissemination of Health Promotion Information in Cooperative Extension:  A multi-study exploration of channels, sources, and characteristics that influence intervention uptake
    Strayer, Thomas Edward III (Virginia Tech, 2019-05-09)
    A translational gap exists between the development of an evidence-based health promotion intervention and its eventual implementation in the intended setting. This lack of translation impacts the uptake of health promotion interventions within delivery systems such as the Cooperative Extension Service (Extension). Within this system, Extension educators serve as the intermediaries addressing needs in the communities in which they are employed with support from Extension health specialists. Previous research has shown that educators utilize other peer educators and specialists to learn and adopt health promotion programming, but these studies are over two decades old (e.g., missing technological advances such as Internet and social media) and often focused on a single state Extension system. The purpose of this research was to understand how evidence-based health promotion intervention information is shared within Cooperative Extension by 1) identifying information sources and channels of Extension specialists and educators while 2) identifying the characteristics of an intervention that aid in the adoption and uptake of these health promotion interventions. The first mixed-methods study aimed to identify information sources and channels used by Extension educators from a national sample and learn their preferences for information delivery. Results of this study (Manuscript 1), identified specialists as the key information source Therefore, the second study (Manuscript 2) focused on Extension health specialists' preferences for information sources and channels while also 1) determine how specialists communicate with educators 2) preliminary thoughts on a dissemination intervention. The final study (Manuscript 3) explored the intervention characteristics that are both educator and specialists deemed most important to their adoption decision-making process. The results of this dissertation inform the development of a dissemination intervention to bridge the translational gap across Extension. The information sources and channels used and trusted by both Extension educators and specialists are highlighted in this work. Additionally, specialists have given insight for consideration for an online repository that can be used on demand to both facilitate the adoption and uptake of health promotion interventions as needed by Extension Educators.
  • Thumbnail Image
    Do Probiotics Protect Against the Deleterious Effects of a High-Fat Diet?
    Fundaro, Gabrielle F. (Virginia Tech, 2014-06-27)
    High-fat diets and obesity have been linked to unfavorable changes in gut bacteria and increased leakage of bacterially-derived lipopolysaccharide (endotoxin) from the intestinal tract into circulation, which is associated with low-grade inflammation, metabolic dysregulation and degradation of tight-junction proteins between intestinal cells. Probiotic supplementation is the practice of ingesting live strains of bacteria that are proposed to have a beneficial effect on the host by enriching the intestine with healthy bacteria. The purpose of this project was to determine if probiotic supplementation would prevent increased inflammatory tone, decreased oxidative capacity, and decreased tight-junction protein expression associated with high-fat feeding and elevated endogenous endotoxin. Male C57BL/6J mice were fed either a control (CD, 10% fat) or high-fat (HFD, 60% fat) diet for 4 weeks while receiving a daily oral gavage of water (C-VSL#3, HF-VSL#3) or probiotics (C+VSL#3, HF+VSL#3) equivalent to 1.2 billion live cultures. Changes in body weight, body composition, respiratory exchange ratio, energy expenditure, and glucose and insulin tolerance were measured in live mice. Markers of metabolic function were measured in whole muscle homgenates and mitochondria isolated from red and white skeletal muscle. Plasma endotoxin was measured in blood collected from fasted mice at the time of euthanization. The large and small intestines were collected and mRNA levels of tight-junction proteins and markers of nutrient sensing were measured. To determine a possible protective effect against endogenous LPS, a second cohort of mice were given an intraperitoneal injection of 0.1µg/kg LPS or saline to induce endotoxemia after four weeks of the aforementioned feeding protocol. Markers of metabolic function and inflammation were measured in mitochondria, skeletal muscle and liver. VSL#3 supplementation improved glucose homeostasis and markers of inflammation while enhancing nutrient sensing in the gut.
  • Thumbnail Image
    Early Skeletal Muscle Adaptations to Short-Term High-Fat Diet in Humans Before Changes in Insulin Sensitivity
    Anderson, Angela S.; Haynie, Kimberly R.; McMillan, Ryan P.; Osterberg, Kristin L.; Boutagy, Nabil E.; Frisard, Madlyn I.; Davy, Brenda M.; Davy, Kevin P.; Hulver, Matthew W. (Wiley-Blackwell, 2015-04-01)
    Objective—The purpose of this investigation was to understand the metabolic adaptations to a short-term (5 days), isocaloric, high fat diet (HFD) in healthy, young males. Methods—Two studies were undertaken with 12 subjects. Study 1 investigated the effect of the HFD on skeletal muscle substrate metabolism and insulin sensitivity. Study 2 assessed the metabolic and transcriptional response in skeletal muscle to the transition from a fasted-to-fed state using a high fat meal challenge prior to and following 5 days of HFD. Results—Study 1 showed no effect of a HFD on skeletal muscle metabolism or insulin sensitivity in fasting samples. Study 2 showed that a HFD elicits significant increases in fasting serum endotoxin, and disrupts the normal postprandial excursions of serum endotoxin, and metabolic and transcriptional responses in skeletal muscle. These effects following 5 days of HFD were accompanied by an altered fasting and postprandial response in the ratio of phosphorylated to total p38 protein. These changes all occurred in the absence of alterations in insulin sensitivity. Conclusions—Our findings provide evidence for early biological adaptations to high fat feeding that proceed and possibly lead to insulin resistance.
  • Thumbnail Image
    The Effect of a Probiotic Supplement on Insulin Sensitivity and Skeletal Muscle Substrate Oxidation during High Fat Feeding
    Osterberg, Kristin (Virginia Tech, 2014-08-28)
    Background: Modifying the gut microbiota through the administration of probiotics during high fat feeding has been shown to attenuate weight gain and body fat accretion while improving insulin sensitivity in animal models. Objective: Our objective was to determine the effects of the probiotic VSL#3 on body weightand composition, skeletal muscle substrate oxidation, and insulin sensitivity and during 4 weeks of high-fat, hypercaloric feeding. We hypothesized that the probiotic would attenuate the body weight and fat gain and adverse changes in insulin sensitivity and substrate oxidation following high fat, hypercaloric feeding in young, non-obese males. Methods: Twenty non-obese males (18-30 y) volunteered to participate in the present study. Following a 2-week eucaloric control diet, subjects underwent a dual x-ray absorptiometry (DXA) to determine body composition, an intravenous glucose tolerance test (IVGTT) to determine insulin sensitivity, a skeletal muscle biopsy for measurement of substrate oxidation. Serum endotoxin was also measured. Subsequently, subjects were randomized to receive either VSL#3 (2 satchets) or placebo during 4 weeks of consuming a high fat (55% fat), hypercaloric diet (+1,000 kcal/day). Macronutrient composition of the high fat diet was 55% fat, 30% carbohydrate, and 15% protein. Results: There were no differences between the groups in subject characteristics or in the dependent variables at baseline. Body weight and fat mass increased less (P<0.045) following the high fat diet with VSL#3 compared to placebo. Insulin sensitivity (and other IVGTT variables) and both glucose and fat oxidation did not change significantly with time or VSL#3 treatment. Serum endotoxin concentration was not different between groups following the high-fat diet. Conclusions: VSL#3, a multi-strain probiotic, attenuated body weight and fat gain following a 4-week high fat, hypercaloric diet compared with a placebo. There were no differences between the VSL and control in circulating endotoxin, insulin sensitivity (and other IVGTT variables) or in skeletal muscle substrate oxidation.
  • Thumbnail Image
    Effect of Capsaicin Supplementation on Performance of and Physiological Response to Repeated Sprinting
    Opheim, Maximilian Nicholas (Virginia Tech, 2010-02-02)
    Aim: Fatigue during team sports requiring multiple sprints can result from the combined effects of metabolic, mechanical, neurological, and immune factors. The purpose of this study was to investigate the influence of capsaicin on performance of and the physiological response to an exercise test simulating the fitness demands of team sport game conditions. Methods: This study was a placebo-controlled, crossover design. Nineteen healthy male experienced athletes age 18-30 yr consumed either 3 g/d cayenne (25.8 mg/d capsaicin) or placebo for 1 wk. Directly following the supplementation period, they completed a repeated sprint test consisting of 15 30 m maximal effort sprints on 35 s intervals. Sprint times were recorded via electronic dual-beam timing system. Fasted blood draws for interleukin-6 (IL-6) were taken at baseline prior to supplementation, 45-min pretest, and immediately post test. Heart rate (HR), blood pressure (BP), rate of perceived exertion (RPE), muscle soreness (MS), and gastrointestinal distress (GD) were measured 1-min pretest, during, posttest, and 1-min posttest. MS was also measured for 3 d posttest. Results: Relative to the placebo, capsaicin significantly reduced maximum HR by 9.3%, total average HR by 8.5%, and sprinting average HR by 6.0% (P<0.05). Capsaicin caused GD of at least 2/5 in 24.5% of subjects. There was no difference between treatments in fastest or mean sprint time, fatigue, percent change or difference in IL-6, BP, RPE, sprint or posttest MS. Conclusion: Capsaicin did not influence repeated sprint performance or the inflammatory response, but reduced HR during intense activity and causes substantial GD.