Literatura académica sobre el tema "Physiological aspects"

Sprint cross-country skiing is a physiologically and technically complex discipline, performed as a time-trial qualification race and three subsequent knock-out heats. The racing time in a single heat is 2-4 min and is comparable to other middle-distance sports. However, sprint skiing is performed in varied terrain at constantly changing intensities using multiple techniques involving the arms and the legs to various degrees. The overall objectives of the current thesis were to examine physiological and biomechanical aspects associated with sprint skiing performance in the skating technique in elite skiers: 1) while treadmill roller skiing in the laboratory (studies I-IV), 2) during sprint competitions on snow (studies IV-V) and 3) for relationships between laboratory characteristics and performance on snow (studies IV-V). Studies I-III are comparative studies in which physiological characteristics, mechanical efficiency and gross kinematics during treadmill roller skiing were compared between male world-class and national level sprint skiers (studies I-II), and between men and women matched for performance level (study III). Study I showed that maximal aerobic capacity, gross efficiency and high speed capacity differentiated world-class from national level sprint skiers. The study also indicated that low and moderate intensity endurance training and maximal speed training is important in attaining an international level in sprint skiing. Study II demonstrated that world-class sprint skiers had a higher gross efficiency than national level skiers. A general linear relationship between work rate and metabolic rate existed, indicating that gross efficiency at moderate and high work rates provides useful information about crosscountry skiers in standardized conditions during treadmill roller skiing. Furthermore, worldclass skiers used longer cycle lengths and lower cycle rates at a given speed and generated higher maximal speeds. In study III, men showed a 17% higher peak treadmill speed at a short and long incremental test compared to women. These gender differences were slightly greater than findings in comparable endurance sports. The majority of gender differences in performance could be explained by higher maximal oxygen uptakes and lower fat percentages in men. Men and women showed similar gross efficiency. However, women showed higher fractional utilization of maximal oxygen uptake at the anaerobic threshold. In studies IV-V, elite male skiers were analyzed for speeds, work rates, technique choices and gross kinematics during two sprint time-trial competitions on snow. Furthermore, the skiers were tested for physiological and kinematical characteristics in the laboratory. Study IV analyzed the time-trial of an international sprint competition. The results showed that performance on uphill and flat terrain strongly determined sprint time-trial performance, and that performance in the last half of the race differentiated most between skiers. Estimated work rates on an uphill section of the race were approximately 60% higher than the capacities which the skiers are able to cover aerobically. Peak oxygen uptake, gross efficiency, peak treadmill speed and peak cycle length were strongly related to sprint time-trial performance, particularly to the uphill and flat sections during the last part of the race. Study V analyzed a simulated sprint race by using a high end differential global navigation satellite system with simultaneous tracking of both GPS and GLONASS satellites. This provided an opportunity for more detailed analysis of cross-country skiing. Skiers encompassed a large speed range (2.9–12.9 m·s-1) and multiple transitions between skiing techniques (range: 21–34 transitions). The results demonstrated that performance in the uphill sections had the strongest correlation to sprint performance, and that the faster skiers used the G3 technique to a greater extent than the slower skiers. Thus, this provides new knowledge on physiological and biomechanical aspects of sprint skating performance, particularly that both the maximal aerobic and peak speed capacities differed between world-class and national level sprint skiers. Furthermore, gross efficiency, while treadmill roller skiing provides relevant information strongly related to sprint performance level. Better skiers also employ longer cycle lengths at the same absolute speeds and at individual peak speeds. The gender differences in performance were slightly larger than expected; however, most of these differences could be explained by a higher maximal oxygen uptake and a lower fat percentage in men. Furthermore, the variations in speeds, work rates and techniques and, especially, speed in uphill and flat terrain are important to the skiers’ total time-trial performance. Better sprint performance is related to more application of the G3 technique and to longer cycle lengths within this technique. Faster skiers showed higher peak oxygen uptake, gross efficiency and high speed capacity. These capacities were specifically correlated to the ability to maintain high speed on uphill and flat terrain throughout a sprint race.<br>Sprintlangrenn er ein fysiologisk og biomekanisk kompleks disiplin som blir utført som ein prolog og tre etterfølgjande utslagsløp. Konkurransetidene i kvart enkelt heat er 2-4 min og kan samanliknast med andre mellomdistanseidrettar. Sprintlangrenn blir imidlertid gjennomført i kupert terreng og med varierande arbeidsintensitet og innslag av ulike teknikkar som involverer underkropp og overkropp i ulik grad. Den overordna målsetjinga med denne avhandlinga var å undersøke fysiologiske og biomekaniske aspekt som er assosiert med prestasjonen i sprint skøyting hos elite langrennsløparar: 1) på rulleskitredemølle i laboratoriet (studia I-IV), 2) i sprintkonkurransar på snø (studia IV-V), og 3) for samanhengar mellom laboratorium-karakteristikkar og sprintprestasjonen på snø (studia IV-V). Studia I-III undersøker forskjellar i fysiologiske karakteristikkar, mekanisk effektivitet og kinematikk mellom mannlege verdsklasse og nasjonal klasse sprintlangrennsløparar (studia III) og mellom mannlege og kvinnelege sprintlangrennsløparar på tilsvarande prestasjonsnivå (studie III). Studie I viser at maksimal aerob kapasitet, mekanisk effektivitet og hurtigheit skil verdsklasse frå nasjonal klasse sprintlangrennsløparar. Studiet indikerer også at låg- og moderat-intensiv uthaldstrening og maksimal hurtigheitstrening er viktig for å nå internasjonalt nivå i sprintlangrenn. Studie II viser at verdsklasse sprintlangrennsløparar har betre mekanisk effektivitet enn løparar på nasjonalt nivå. Studiet viser ein generell lineær samanheng mellom arbeidsratar og energiforbruk og indikerer at målingar av mekanisk effektivitet gir nyttig og valid informasjon om langrennsløparar som blir samanlikna under standardiserte vilkår på rulleskitredemøller. Studiet demonstrerer også at verdsklasse løparane har lengre sykluslengder og lågare syklusfrekvens på ei gitt fart. Studie III viser at menn oppnår 17 % høgre fart enn kvinner både på ein kort og ein lang prestasjonstest med trinnvis aukande fart på rulleskitredemølla. Resultata indikerer at prestasjonsforskjellane mellom kjønna hovudsakleg kan forklarast av høgare maksimalt oksygenopptak og lågare feittprosent hos menn, og at forskjellane er noko større enn det litteraturen viser i andre tilsvarande uthaldsidrettar. Kvinner og menn har lik effektivitet, mens kvinner har høgare prosentvis utnytting av maksimalt oksygenopptak ved anaerob terskel. I studia IV-V vart fart, arbeidsratar, teknikkval og kinematikk undervegs i sprintkonkurransar undersøkt. Vidare blei samanhengar mellom fysiologiske og kinematiske karakteristikkar i laboratoriet og sprintprestasjonen på snø undersøkt. I studie IV vart prologen i ein internasjonal sprintkonkurranse analysert. Resultata viser at prestasjonen i motbakke og i flatt terreng er sterke forklaringsvariablar for den totale prologprestasjonen. Studiet indikerer også at prestasjonen i siste halvdelen av løypa skil løparane mest. Estimerte arbeidsratar i motbakke indikerer eit totalt arbeid omlag 60% høgare enn det løparane klarer å dekke med aerob energi. Maksimalt oksygenopptak, mekaniske effektivitet, fartskapasitet og sykluslengde var sterkt relatert til sprintprestasjonen, og spesielt til farta i flatt terreng og motbakkar i siste halvdelen av løpet. I studie V vart ein simulert sprintprolog analysert ved bruk av ein høgteknologisk differensial GPS, med svært høg samplingsfrekvens og nøyaktigheit, som hadde samtidig mottak av GPS- og GLONASS-satellittar. Løparane gjennomførte sprintkonkurransen i variert terreng, noko som førte til eit spenn i hastigheiter frå 2.9 til 12.9 m·s-1 og som inkluderte 21–34 teknikkendringar. Motbakkeprestasjonen var høgast korrelert til total prestasjon, og betre skiløparar brukte dobbeldansteknikken i større grad, samanlikna med mindre gode løparar. Samanfatta så bidreg denne avhandlinga med ny kunnskap om fysiologiske og biomekaniske aspekt av sprintlangrenn i skøyting. Det viser at både maksimal aerob kapasitet og fartskapasitet skil verdsklasse frå nasjonal klasse sprintlangrennsløparar. Det er også vist at målingar av mekanisk effektivitet på rulleskitredemølle gir valid informasjon og er sterkt relatert til prestasjonsnivået til løparane. Dei beste løparane bruker lengre sykluslengder både på same submaksimale fart og på si høgste individuelle fart. Forskjellane mellom mannlege og kvinnelege sprintløparar i prestasjon er noko større enn forventa. Det meste av desse kjønnsforskjellane kan forklarast av at menn har høgare maksimalt oksygenopptak og lågare feittprosent. Undervegs i sprintprologar viser løparane store variasjonar i fart, arbeidsratar og vekslar stadig mellom ulike teknikkar. Spesielt er farta i motbakkar og flatt terreng mot slutten av løpa betydningsfull for prologprestasjonen. Betre prologprestasjon er linka til meir bruk av dobbeldansteknikken og lengre sykluslengder innan denne teknikken. Betre utøvarar har også høgare maksimalt oksygenopptak, effektivitet og fartskapasiet, noko som vart relatert til evna til å oppretthalde høg fart i motbakkar og flatt terreng gjennom eit sprintløp.

The effect of the key physiological parameters on the production of solvents in the acetone-butanol fermentation using the anaerobic bacterium Clostridium acetobutylicum was examined in this work.<br>The theoretical solvent yield was calculated based on expressing stoichiometric relationships between the substrate and the products of the process. The maximum theoretical yield under the acceptable process conditions was established ranging from 38.6% to 39.9%.<br>A linear correlation was established between the production of solvents and gases which varied with the mixing rate of the fermentation system.<br>Elevated hydrogen partial pressure affected the metabolism of C. acetobutylicum resulting in increased butanol and ethanol yields (based on glucose) by an average of 18% and 13%, respectively.<br>A mathematical model for the batch acetone-butanol fermentation was formulated using original experimental data for the microbial growth, sugar consumption and metabolite biosynthesis. This model was used for computer process simulations. Parametric sensitivity analysis indicated the importance of the key process parameters.<br>A method of systems analysis was applied in analysing pronounced physiological differences in the performance of one of the C. acetobutylicum culture strains. The cellular transport mechanism for substrate (glucose), solvents and acids through the cell membrane was established to depend on its permeability and the number of sugar transport "sites". Experimental results obtained from the study of the uptake of 3-0-methyl glucose (0.7mM) by the "normal culture" and the "retarded culture" confirmed the theoretical predictions of a slower transpost in the "retarded culture". The theoretical predictions were further confirmed by additional experimental results.<br>A mathematical "Physiological State Model" was developed which includes the culture physiological parameters as well as the internal and the external culture conditions. Using this mathematical model the standard and the substandard acetone-butanol fermentations could be simulated.<br>These results demonstrate the application of the method of systems analysis in elucidation of the role played by the key culture physiological parameters in the fermentation process.

Obesity continues to be a major cause of morbidity and mortality and worldwide prevalence rates continue to rise. The cornerstone for treating obesity remains diet and lifestyle, with the ultimate goal being normalising those parameters that are associated with ill health, for example hyperinsulinaemia and insulin resistance. Because obesity predominantly develops due to a mismatch between energy intake and utilisation, this thesis looked at the effects of dietary interventions upon Resting Energy Expenditure (REE) and substrate oxidation. In addition, the impact of popular dietary interventions upon body composition and insulin resistance was examined. When phenotypic characteristics were investigated before and after weight loss by using hypocaloric diets, which differed in fat and carbohydrate content, Fat-Free Mass (FFM) and Fat Mass (FM), were strong predictors of REE before and after the intervention and weight loss rather than the specific dietary intervention, significantly predicted post intervention REE. Fasting fat oxidation was found to be lower in obese subjects and they had a lower postprandial response to a high fat challenge. This implied that a diet high in fat is more likely to promote a positive energy balance an ultimate weight gain. The final study compared 4 popular dietary interventions. Each was equally effective at achieving clinically significant weight loss and improvements in insulin sensitivity. Although none was significantly more superior, there was a trend supporting three of the diets (Atkins’, Weight Watchers and Rosemary Conley) above the other (Slim-Fast) and it was the pattern of weight loss, i.e. mainly loss of FM, which proved beneficial with regards to improving insulin sensitivity. In summary, this thesis confirms that REE is mainly predicted by FFM and FM and that there is diminished fat oxidation on obese subjects. What this thesis also adds to previous research that it if a specific diet can improve the pattern of weight loss, this can be clinically beneficial.

The intake of water and electrolytes is inseparable from feeding by natural or artificial means and careful attention to salt and water balance is a vital component of perioperative care and of nutritional support. Nutritional support with water and sodium restriction in post-intensive care patients with oedema, dilutional hypoalbuminaemia and fluid excess of 10 L, cleared oedema over 7-10 days, with a 1 g/L rise in serum albumin for every kg loss in weight. Return of gastrointestinal function was also observed. Accordingly, 20 patients, undergoing colonic surgery, were randomised to receive standard (>3 L water and 154 mmol sodium/day) or restricted postoperative fluids (<2 L water and 77 mmol sodium/day). Solid (72.5 vs 175 min) and liquid phase (73.5 vs 110 min) gastric emptying times were significantly longer in the standard group on the 4th postoperative day and associated with a three day longer hospital stay. In volunteers receiving 2 L of 0.9% saline and 5% dextrose infusions, on separate occasions over one hour, haematocrit and serum albumin concentration fell, mainly due to dilution. While dextrose was rapidly excreted, two-thirds of the saline was retained after 6 h. Following 1 L infusions, plasma renin and angiotensin concentrations decreased more after saline than dextrose (P<0.04). Responses of aldosterone, atrial natriuretic peptide and vasopressin were not significantly different. Comparing 2 L infusions of saline and Hartmann's solution, volunteers excreted more water (median 1000 vs 450 mL) and sodium (122 vs 73 mmol) after Hartmann's. Hyperchloraemia and reduced bicarbonate were noted after saline alone. Whereas fluctuations in water balance are dealt with efficiently through osmoreceptors and vasopressin, and sodium deficiency by volume receptors and the renin angiotensin aldosterone system, the mechanism for dealing with sodium and chloride excess appears relatively inefficient. Natriuretic peptide responds to volume expansion rather than sodium gain.

1. The septal structure of <i>C. cinereus</i> and <i>N. crassa</i> was examined via fluorescence microscopy and transmission electron microscopy. The septa of these organisms were shown to contain two plates of chitin, not one, as had been previously believed.2. The effect of the fluorochrome Calcofluor White on chitin synthesis <i>in vivo</i> and <i>in vitro</i> was investigated. Growth of <i>C. cinereus</i> in media seeded with the dye caused abnormal deposition of chitin at points of growth i.e. tips, septa, hook cells and clamps. However, high concentrations of the dye were required to have an effect on the chitin content and growth rate of the mycelium. X-ray crystallography showed that chitin synthesized in the presence of the fluorochrome was less crystalline than chitin synthesized when the dye was absent. It would appear, therefore, that Calcofluor binds to nascent chitin inhibiting its crystallization into microfibrils. It was concluded that chitin synthesis is a two-step process involving polymerization and subsequent crystallization.3. A range of fungi and growth forms were probed for the presence of actin using the actin-specific fluorochrome rhodamine phalloidin. Only <i>U. phaseoli</i> germlings and <i>C. albicans</i> yeast cells appeared to contain the protein. It is suggested that the failure to visualize actin in the other organisms examined is linked to their cell wall structure which prevented penetration of the rhodamine phalloidin to sites of actin localization.4. In the light of these results, mechanisms of hyphal growth are discussed and a model for the polarity of apical extension is presented.