1,720,976 research outputs found
The Effects of a Progressive Dehydration Protocol on Glycaemic Response During and Following Exercise in Patients with Type 1 Diabetes
Full text linkThe aim of this study was to assess whether progressively dehydrating Type 1 Diabetes Mellitus (T1DM) patients via fluid restriction around exercise affected glucose control during and following exercise, compared to euhydrated T1DM patients. It is hoped that this study can aid the formation of T1DM-specific fluid intake guidelines around exercise, based on alterations in glucoregulation and osmoregulation.
The fluid restriction protocol induced a mild level of dehydration (1.1% body mass loss from pre-exercise measurements). Furthermore, dehydrated subjects displayed significantly greater post-exercise serum copeptin concentration (p<0.01), compared to resting and euhydrated subjects’ values. There was a trend for a greater glycaemic response during exercise and the post-exercise recovery period of the dehydration trial, but there were no significant differences in either the interstitial or blood glucose responses between trials. Although baseline serum glucagon concentrations were significantly different between trials (p<0.01), thereafter there were no significant differences between trials at any remaining timepoint. There was a statistically significant effect of trial on serum cortisol concentrations (p<0.01), with post-exercise serum cortisol concentrations remaining significantly greater during the dehydration trial, compared to euhydrated subjects’.
Up to 48 hours following the dehydration trial, there was a significantly reduced prevalence of mild hyperglycaemia compared to the same period following the control trial (p<0.01), with a trend for a concomitant increase in euglycaemic interstitial glucose measurements. The discrepancies in acute glycaemic control occurred without an increased risk of hypoglycaemia, and were not attributable to any significant differences in total carbohydrate intake or total units of insulin administered. Further research is required to establish the intramuscular and intracellular physiology linking dehydration with alterations in whole-body and tissue-specific glucose metabolism. T1DM patients must therefore balance the potential short-term benefits of mild dehydration on acute glycaemic control, with long-term health consequences associated with regular dehydration and elevated vasopressin concentrations
Fluid and electrolyte balance during indoor tennis match play
Full text linkFluid intake, electrolyte balance, and effort intensity during one best of three set indoor singles tennis match (17 ± 2°C, 42 ± 9% humidity) was measured in 16 male University tennis players. Sweat samples were collected through application of an absorbent sweat patch to the forearm, calf, thigh and back of each player. Effort intensity was measured through comparisons of on-court heart rates to data obtained from a maximal treadmill test.
The mean sweat loss was 1219 ± 417 ml, mean fluid intake was 1087 ± 625 ml (players replaced on average 89% of fluid lost), mean whole body sweat rate was 0.72 ± 0.26 l/h and no significant body mass loss was observed from pre to post match. However, a large inter-individual variability existed (range 0.43 - 1.28 l/h). 15 out of 16 players chose to consume water during their match; and these fluid intake choices were sufficient to on the whole maintain plasma sodium levels. Two players provided pre-match urine samples above 900 mOsmol/kg while another four provided samples approaching this level, indicating some players were hypohydrated prior to match play. The mean sweat sodium concentration was 41 ± 15 mmol/l suggesting lower heat acclimation statuses than in players competing at warmer environments, and total sodium losses during match play were 1.12 ± 0.45 g (range 0.46 – 1.93 g). Again, large individual variations existed. On average, dietary and on-court electrolyte intake exceeded electrolyte loss during match play by a considerable margin, but in some player’s there was not a great difference. Muscle cramping could occur if players fail to adequately replace both fluid and electrolyte losses that occur during match play, even in a comfortable indoor environment. Finally, indoor match play largely consisted of moderate intensity exercise, below ventilatory threshold, with a smaller high intensity contribution.
This study showed that in cool ambient conditions, sweat rates reached 1.28 l/h, and players ingested sufficient fluid to replace 89 ± 47% of sweat losses, suggesting that contrary to footballers, runners, and in some other sports, fluid replacement is easier to achieve in tennis due to the regular breaks in match play
Training intensity distribution, physiological adaptation and immune function in endurance athletes
Full text linkExercise intensity and its distribution is probably the most important and most heavily debated variable of endurance training. Training induces adaptation but also induces stress responses. Controlling the training-intensity distribution may provide a mechanism for balancing these two effects. It has been reported that elite endurance athletes train with a high volume and load, relative to the sport. These athletes spend the vast majority (>80%) of training time at relatively low intensities (lower than the lactate threshold, zone one), and therefore <20% of training time above the lactate threshold (zones two and three). Experimental studies support the beneficial effects of a high training volume in zone one, and show detrimental effects of replacing zone one training with training in zone two. This is likely due to enhanced recovery from training in zone one compared with training in zone two. The acute recovery following training sessions in zones two and three has been reported to not be different, but the recovery following training in zone one has been reported to be faster. Improvements in physiological adaptation and endurance performance have been reported to be greater following training programmes with higher exercise intensities. Therefore, it has been suggested that a polarised training model, which includes ~80% of training in zone one with ~20% of training in zone three is more beneficial than a threshold training model, with the majority of training in zone two. However, research into an optimal training-intensity distribution is limited. Therefore, the aims of this thesis were to assess the effectiveness of training-intensity distribution on the improvements in physiological adaptation, endurance performance and assess if manipulating training-intensity distribution had an effect on immune function.
Study one revealed that the lactate threshold, the lactate turnpoint and maximal performance measures in swimming, cycling and running, assessed using the methods outlined in the study, are reproducible in trained endurance athletes. These tests can therefore be used by trained endurance athletes as part of a physiological testing programme to assess not only endurance performance, but also to demarcate training intensity zones for exercise intensity prescription and monitor moderate to large adaptations to training. Practitioners should take care when deciding on the duration between tests to test for adaptations from training, as adaptations need to be greater than these detected test-retest variations to be considered physiologically meaningful.
To the best of the author’s knowledge, study two was the first study to have assessed training-intensity distribution in a group of multisport athletes. Training was monitored over a 6-month period, and testing took place every two months to assess the effect of the training on physiological adaptation. Although speculative due to the number of variables involved, the results suggest that a greater proportion of training time spent in zone one and a lower proportion of training time spent in zone two is beneficial to physiological adaptation. However, given the number of variables associated with assessing the training-intensity distribution in multisport athletes, it is not easy to draw conclusions as to the effectiveness of the training in the different disciplines on the key measures of adaptation in the different disciplines. Study two highlighted the need for future research to focus on experimental manipulation of training-intensity distribution and thus improve our understanding of its impact on the training-induced adaptations in endurance athletes.
Study three manipulated the training-intensity distribution in trained endurance athletes in just one discipline, to reduce the number of variables involved. A polarised training model was compared to a threshold training model on the effectiveness to improve physiological adaptation and endurance performance. Results revealed that a polarised training model is recommended for trained cyclists wishing to maximally improve performance and physiological adaptation over a short-term (six week) training period.
The first part of study four assessed the effect of a polarised and a threshold training model on immune function markers in trained cyclists. Both endurance training programmes had similar volume, and were sufficient to induce improvements in performance and physiological adaptation. However, despite likely differences in recovery, both training programmes had no effect on the proportion of low or high differentiated or senescent CD8+ or CD4+ T-cells in blood. Therefore, training adaptation was achieved at no cost to this particular aspect of immune function. From these results and evidence from previous studies, it seems likely that athletes need to be overreached to induce any change in immune function following a period of intensified training.
The second part of study four assessed the impact of an ironman triathlon race on Epstein-Barr virus (EBV) and Varicella-Zoster virus (VZV) antibody titres and the frequency of low and high differentiated and senescent blood T-cells in trained endurance athletes. Previous work has revealed that an ironman triathlon race increases the proportion of senescent CD4+ T cells and decreases the proportion of naive CD4+ T cells, and thus induces changes the immune space which could leave an individual at a greater risk of infection. This study however, did not find any changes in the proportions of these T cell subsets following an ironman triathlon race. The mean results of this study suggest that there is no relationship between EBV and VZV-specific antibody concentrations and the proportion of senescent, low and highly differientiated T cells. However, on analysis of individual subject data, it seems possible that subjects with a high antibody titre for EBV or VZV 3 wks before a competition might be more at risk of infection post race. A greater subject number would be needed in order to make a more conclusive statement about this relationship.
The results of this thesis suggest that future research is required in the area of training-intensity distribution. Firstly, our understanding of the physiological mechanisms responsible for the effectiveness of a polarised training model in trained endurance athletes is limited, and thus studies should attempt to address this issue. Our current knowledge on the mechanisms underlying a blunted T cell response following strenous exercise is also limited. A change in the immune space to a greater proportion of senescent T cells and a lower proportion of naive T cells might contribute to this blunted response. In the current thesis however, the proportions of these T cell markers were unchanged following the training/racing interventions. It is possible that with a higher training load, there could be changes in these markers, and thus this is an exciting area that could have potential implications on athlete health. Finally, testing for antibody titres in endurance athletes is possibly an avenue to detect individuals at the greatest risk of infection if subjected to a large physical and/or mental stress. This could have implications on maintaining athlete health and therefore, allowing athletes to train consistently
The Breakfast Rise, Education and Knowledge Study in Children and Young People who have Type 1 diabetes (T1D): The BREAK Study
No full textBackground
Children and Young People (CYP) with type 1 diabetes (T1D) often experience glucose variability (GV) and postprandial hyperglycaemia after breakfast.
Aim
The aim of the study was to describe glucose variability (GV) and to investigate postprandial glycaemia and the relationship with food composition following breakfast in CYP with T1D.
Methods
In an observational study, CYP with T1D were invited to share their continuous glucose monitoring (CGM) data and to submit seven-day questionnaires about their breakfast meal and the four-hour postprandial period. In a randomised crossover intervention CYP with T1D were invited to test the following breakfast meals twice: high glycaemic load (GL) (HGL meal), HGL with 10g of added protein (HGLP meal) and medium GL (MGL meal). Control meals were the participants usual breakfast. CGM data was collected for the three-hour postprandial period. Statistical analysis included t-tests and linear mixed models. A survey of dietitian’s experience of postprandial glucose after breakfast was also undertaken.
Results
89 CYP were recruited to the observation study of which 74 submitted questionnaires. Diurnal GV (%CV) was significantly higher than nocturnal GV (38.1 ±4.3% vs. 36.4 ±5.2%, p<0.001). Data on 387 breakfast meals was analysed. Pre-prandial glucose was significantly higher for the multiple daily injection (MDI) users (9.5±2.9; 10.2±3.2 mmol/l) compared with insulin pump users (7.4±2.3; 8.8±2.5) (p<0.01). Pre-prandial glucose was significantly associated with the mean postprandial glucose (R2=0.27, p<0.001). Ingested meals which contained only breakfast cereals resulted in significantly higher glucose excursion at 30 (p<0.001), 60 (p<0.001) and 90 minutes (p=0.02) compared with meals which included a protein food.
25 CYP were recruited to the intervention study. At 30 and 60 minutes, the ingestion of the HGL meal resulted in a significantly higher glucose excursion compared with all other breakfast meals (p≤0.01). This remained significantly higher than after the ingestion of the HGLP meals at 90 and 120min (p<0.01). The results were comparable for those using Hybrid Closed Loops systems.This work was sponsored by Rachel Beaton, University of Stirlin
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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