Exercise-nutrient interactions: Effects on substrate metabolism and performance

During prolonged (> 90 min), continuous steady-state exercise, skeletal muscle is fuelled by both carbohydrate (CHO) (i.e. muscle and liver glycogen, blood glucose and muscle, blood and liver lactate) and fat substrates (i.e. adipose and intramuscular triglycerides [IMTGs], blood-borne free fatty acids [FFAs] and TGs). The specific pattern of substrate oxidation is influenced by the relative exercise intensity, an individual’s training status and their preceding diet. However, it is well accepted that when exercising at high relative intensities (i.e. > 70% maximal oxygen uptake [V̇ O2max]), CHO-based fuels are the predominant fuel source. Despite CHO being important for sustaining prolonged exercise, recent attention has focused on exercise-nutrient protocols that reduce skeletal muscle dependence on CHO fuel sources and, instead, increase reliance on fat-based fuels. Such strategies include high-fat, low-CHO diets, training with low endogenous and exogenous CHO availability and oral ketone supplementation. In theory, strategies that “spare” the oxidation of CHO substrates should enhance endurance exercise performance. This thesis comprises a series of independent but related studies investigating the effects of manipulating both endogenous and exogenous fat availability on substrate metabolism, skeletal muscle adaptations and exercise performance. Study 1 (described in chapter 4) investigated the effect of decreasing circulating FFA availability prior to and during half-marathon running. FFA availability was suppressed via the administration of nicotinic acid, ingested prior to and during exercise. The suppression of lipolysis and the exercise-induced rise in plasma FFAs did not impair half-marathon running capacity. When running at ~80% V̇ O2max for ~90 min there was a small but obligatory use of fat substrates, independent of CHO intake pre- and during exercise. However, CHO was the predominant fuel source, contributing between 80-90% to total energy expenditure. Study 2 (described in chapter 5) examined the effects of ingesting a ketone diester on circulating ketone bodies, substrate metabolism and cycling performance under nutritional conditions replicating an elite professional cycling time-trial. Ketone ingestion increased circulating β-hydroxybutyrate and acetoacetate concentrations. Despite optimal nutritional support, the ketone diester was also associated with gut discomfort and an increased perception of effort, leading to an impairment of cycling time-trial performance. Study 3 (described in chapter 6) manipulated endogenous fat and CHO availability via daily energy intake, to determine whether the metabolic perturbations from a high-fat diet are driven by high-fat or low-CHO availability. Participants consumed five days of a high-fat or highprotein diet (~65% energy intake), while ‘clamping’ CHO consumption to < 20% energy intake. When compared to an isoenergetic high-protein diet, five days’ adaptation to a high-fat diet resulted in greater whole-body rates of fat oxidation during submaximal cycling and decreased skeletal muscle mitochondrial respiration supported by octanoylcarnitine and pyruvate as well as uncoupled respiration at rest. Following one day of a high-CHO diet mitochondrial respiration returned to pre-diet, however whole body rates of substrate oxidation were only partially rescued. This series of research studies contributes new knowledge to the literature by demonstrating that 1) fat substrates contribute < 20% to energy expenditure during prolonged, high-intensity running, independent of pre-exercise CHO intake 2) ketone diester ingestion impairs cycling time trial performance and is associated with a higher perception of effort, despite optimal nutritional feeding and 3) high dietary fat rather than low-CHO intake contributes to reductions in mitochondrial respiration and increases in whole-body rates of fat oxidation following a high-fat, low-CHO diet. However, this reduction can be partially rescued following one day of a high-CHO diet. This novel information provides evidence that high-fat diets and exogenous ketone drinks are not advantageous for an athletes training and competition due to their detrimental effects on substrate metabolism and skeletal muscle adaptations. Athletes should instead ensure high-CHO availability prior to and during competition to maximise whole-body rates of CHO oxidation rates

Modeling the Effects of Beam Size and Flaw Morphology on Ultrasonic Pulse/Echo Sizing of Delaminations in Carbon Composites

The size and shape of a delamination in a multi-layered structure can be estimated in various ways from an ultrasonic pulse/echo image. For example the -6dB contours of measured response provide one simple estimate of the boundary. More sophisticated approaches can be imagined where one adjusts the proposed boundary to bring measured and predicted UT images into optimal agreement. Such approaches require suitable models of the inspection process. In this paper we explore issues pertaining to model-based size estimation for delaminations in carbon fiber reinforced laminates. In particular we consider the influence on sizing when the delamination is non-planar or partially transmitting in certain regions. Two models for predicting broadband sonic time-domain responses are considered: (1) a fast "simple" model using paraxial beam expansions and Kirchhoff and phase-screen approximations; and (2) the more exact (but computationally intensive) 3D elastodynamic finite integration technique (EFIT). Model-to-model and model-to experiment comparisons are made for delaminations in uniaxial composite plates, and the simple model is then used to critique the -6dB rule for delamination sizing

Managing bereavement in the classroom: a conspiracy of silence?

The ways in which teachers in British schools manage bereaved children are under-reported. This article reports the impact of students' bereavement and their subsequent management in primary and secondary school classrooms in Southeast London. Thirteen school staff working in inner-city schools took part in in-depth interviews that focused on the impact of bereaved children on the school and how teachers responded to these children. All respondents had previously had contact with a local child bereavement service that aims to provide support, advice, and consultancy to children, their parents, and teachers. Interviews were audiotaped, transcribed verbatim, and analyzed using ATLAS-ti. Three main themes were identified from analysis of interview data. Firstly, British society, culture, local communities, and the family were significant influences in these teachers' involvement with bereaved students. Secondly, school staff managed bereaved students through contact with other adults and using practical classroom measures such as "time out" cards and contact books. Lastly, teachers felt they had to be strong, even when they were distressed. Surprise was expressed at the mature reaction of secondary school students to deaths of others. The article recommends that future research needs to concentrate on finding the most effective way of supporting routinely bereaved children, their families, and teachers

A Model-Based, Bayesian Solution for Characterization of Complex Damage Scenarios in Aerospace Composite Structures

Ultrasonic damage detection and characterization is commonly used in nondestructive evaluation (NDE) of aerospace composite components. In recent years there has been an increased development of guided wave based methods. In real materials and structures, these dispersive waves result in complicated behavior in the presence of complex damage scenarios. Model-based characterization methods utilize accurate three dimensional finite element models (FEMs) of guided wave interaction with realistic damage scenarios to aid in defect identification and classification. This work describes an inverse solution for realistic composite damage characterization by comparing the wavenumber-frequency spectra of experimental and simulated ultrasonic inspections. The composite laminate material properties are first verified through a Bayesian solution (Markov chain Monte Carlo), enabling uncertainty quantification surrounding the characterization. A study is undertaken to assess the efficacy of the proposed damage model and comparative metrics between the experimental and simulated output. The FEM is then parameterized with a damage model capable of describing the typical complex damage created by impact events in composites. The damage is characterized through a transdimensional Markov chain Monte Carlo solution, enabling a flexible damage model capable of adapting to the complex damage geometry investigated here. The posterior probability distributions of the individual delamination petals as well as the overall envelope of the damage site are determined

Estimate of control voltage tolerances for a photo-electron analyzer of toroidal design

Sem informaçãoWe have run electron optics simulations and determined the tolerance in the control voltages of all elements (retarding input lens, analyzer, accelerating exit lens) of the La Trobe University photoelectron analyzer, recently redesigned to reach a spectral resolution of 5000, and which will be installed at LNLS (Campinas Brasil) and BESSY II (Berlin, Germany).We have run electron optics simulations and determined the tolerance in the control voltages of all elements (retarding input lens, analyzer, accelerating exit lens) of the La Trobe University photoelectron analyzer, recently redesigned to reach a spectral resolution of 5000, and which will be installed at LNLS (Campinas Brasil) and BESSY II (Berlin, Germany).We have run electron optics simulations and determined the tolerance in the control voltages of all elements (retarding input lens, analyzer, accelerating exit lens) of the La Trobe University photoelectron analyzer, recently redesigned to reach a spectral resolution of 5000, and which will be installed at LNLS (Campinas Brasil) and BESSY II (Berlin, Germany).334788791Sem informaçãoSem informaçãoSem informaçã

Measurement of the Neutron Radius of Pb-208 through Parity Violation in Electron Scattering

We report the first measurement of the parity-violating asymmetry A(PV) in the elastic scattering of polarized electrons from Pb-208. APV is sensitive to the radius of the neutron distribution (R-n). The result A(PV) = 0.656 +/- 0.060(stat) +/- 0.014(syst) ppm corresponds to a difference between the radii of the neutron and proton distributions R-n - R-p = 0.33(-0.18)(+0.16) fm and provides the first electroweak observation of the neutron skin which is expected in a heavy, neutron-rich nucleus

Altering fatty acid availability does not impair prolonged, continuous running to fatigue: evidence for carbohydrate dependence

We determined the effect of suppressing lipolysis via administration of nicotinic acid (NA) on fuel substrate selection and half-marathon running capacity. In a single-blinded, Latin square design, 12 competitive runners completed four trials involving treadmill running until volitional fatigue at a pace based on 95% of personal best half-marathon time. Trials were completed in a fed or overnight fasted state: 1) carbohydrate (CHO) ingestion before (2 g CHO·kg−1·body mass−1) and during (44 g/h) [CFED]; 2) CFED plus NA ingestion [CFED-NA]; 3) fasted with placebo ingestion during [FAST]; and 4) FAST plus NA ingestion [FAST-NA]. There was no difference in running distance (CFED, 21.53 ± 1.07; CFED-NA, 21.29 ± 1.69; FAST, 20.60 ± 2.09; FAST-NA, 20.11 ± 1.71 km) or time to fatigue between the four trials. Concentrations of plasma free fatty acids (FFA) and glycerol were suppressed following NA ingestion irrespective of preexercise nutritional intake but were higher throughout exercise in FAST compared with all other trials (P < 0.05). Rates of whole-body CHO oxidation were unaffected by NA ingestion in the CFED and FAST trials, but were lower in the FAST trial compared with the CFED-NA trial (P < 0.05). CHO was the primary substrate for exercise in all conditions, contributing 83-91% to total energy expenditure with only a small contribution from fat-based fuels. Blunting the exercise-induced increase in FFA via NA ingestion did not impair intense running capacity lasting ∼85 min, nor did it alter patterns of substrate oxidation in competitive athletes. Although there was a small but obligatory use of fat-based fuels, the oxidation of CHO-based fuels predominates during half-marathon running