The aims of this thesis were to: 1) to review research in the area of repeated sprint (RS) performance and diurnal/circadian rhythmicity; 2) to develop a new RS protocol that conforms to field based team sport time-motion analysis and determine its reliability and compare this with a RS protocol previously utilised in the literature; 3) to assess the sensitivity of the RS protocol following acute altitude exposure and simulated soccer specific exercise 4) to investigate diurnal variation of RS performance and assess whether modulating rectal and/or muscle temperatures lead to changes in RS performance. A review of the published research literature investigating the relationship between RS performance and time-of-day variation was conducted. Six studies made it through the whole analysis process for systematic review. It was established that there was evidence to support a late/early afternoon peak in peak power in RS performance around the peak of the rhythm of core temperature. However, there is a clear demand for more rigorous investigations which control factors specifically related to chronobiological investigations. A reliability study was then performed using running as the mode of exercise for the RS test using two different RS protocols to determine the number of trials required to establish high levels of reliability. The first RS test (consisting of a total of 10 sprints, 6-s in duration with 30-s of passive recovery) was a commonly used protocol in the literature and the second was a newly created RSA protocol which is better representative of field based team sports activity (consisting of a total of 10 sprints, 3-s in duration with 30-s of passive recovery). It was established that a number of performance measures of RSA non-motorised treadmill running in both protocols were reliable. However, measures of fatigue were not. Further, it was found that both protocols took 3 sessions to fully familiarise individuals. The main aim of the next study was to investigate the sensitivity of the RSA protocol by examining the effect of altitude and fatigue on RS performance. The first finding was that acute altitude exposure reduces RS performance by 3.1 to 6.5% at 1500-m and 6.2 to 12.8% at 3000-m. The second finding was that RS performance was reduced by 4.6 to 5.8% in a fatigued state. The newly created RS performance protocol is sensitive enough to detect a negative change following altitude acute exposure and a 90-min football-specific intermittent treadmill fatiguing protocol. A diurnal protocol was then employed in order to address the clear demand for more rigorous investigations in chronobiological studies of RS performance. A total of 20 participants took part in this study and it was found that RS performance was significantly higher in the evening compared to the morning ranging from 3.3 to 8.3% in all measures except fatigue index. Diurnal variation now established in RS performance, two studies assessed whether modulating rectal and/or muscle temperature leads to a change in RS performance and further determine how much can be attributed to the influence of an endogenous, temperature-dependent component. The first study (n = 12) established that raising morning rectal temperature to evening values by active warm-up did not increase RS performance to evening values. However, lowering evening rectal or muscle temperatures to morning values by pre-cooling decreased RS performance to values normally observed in the morning. The second study (n = 12) found passively raising morning rectal temperature to evening values, or passively raising morning and evening rectal temperatures to 38.5ºC did not increase RS performance nor offset diurnal variation. Both studies concluded that although central temperature may provide some endogenous rhythm to RSA, the exact mechanism(s) for a causal link between central temperature and human performance are still unclear, and may involve multiple of components and mechanisms.

The body of evidence investigating post-exercise changes in left (LV) and right ventricular (RV) structure and function, commonly referred to as exercise induced cardiac fatigue (EICF), demonstrates a reduction in both systolic and diastolic function. RV dilatation and reduced LV filling are also evident. The mechanism responsible for this phenomenon is not fully understood, however a recent theory suggests that an elevated afterload on the RV and subsequent interaction between the ventricles may be implicated. Based on this, the aims of this thesis were: 1) to assess the RV structural and functional response to a 100 mile ultra-marathon applying novel techniques to determine the transient or persistent nature of RV post-exercise changes, 2) to provide a holistic assessment of all cardiac chambers, including the simultaneous derivation of structure and function for both the LV and RV in the same cardiac cycle following a 100 mile ultra-marathon, 3) to establish the acute response to a 100 mile ultra-marathon in both the 12-lead ECG and right-sided ECG and 4) to assess RV structure and function during a 6 hour upright cycling exercise bout, including the simultaneous estimation of PAP. The key finding from the Chapter 3 was a 10% reduction (P = 0.007) in RV strain and early diastolic strain rate immediately post-race that remained depressed following 6 hours of recovery. The application of area-deformation loops in Chapter 4 highlighted a leftward shift of the LV loop and rightwards shift of the RV loop immediately post-race with concomitant reduction in both LV and RV strain (-29 to -26% and -23 to -19% respectively, P = 0.01). The LV loop reflected a change in cardiac mechanics immediately post-race, supported by the increase in the systolic-diastolic strain gradient (P < 0.05). Following 6 hours of recovery, the strain gradient returned to baseline values but both RV and LV loops were still displaced from baseline values. There was a 22% elevation in the ST segment in leads V2R and V3R following the 100 mile ultra-marathon in Chapter 5. A heterogeneous response was observed with respect to T wave changes with 50% of right-sided ECGs demonstrating a significant change pre to post-race. The laboratory based study in Chapter 6 established the most appropriate technique with respect to reliability, feasibility and appropriate absolute values to quantify RV function during exercise. MST and TVI provide disparate RV strain values at 50 (25 and 30%), 70 (20 and 35%) and 90% (15 and 32%) maximum heart rate. CoV for global RV strain during exercise ranged from 7 to 11% for TVI and 14 to 73% for MST. In Chapter 7, the RV in-exercise response was assessed throughout prolonged cycling exercise with concomitant estimation of RV afterload. In contrast to the field-based studies, an initial increase in RV strain (-26 to -28%) was maintained as exercise progressed with no elevation in RV afterload or subsequent structural adaptation.

The physical demands of soccer match play have been extensively studied. Muscle glycogen is the major energy source required to meet these demands and strategies to maximise this provide clear performance benefits to match play. Such information has allowed sports nutritionists to develop specific guidelines to optimise physical performance and recovery. However, the physical demands of soccer training have only recently started to be examined. For this reason, Study 1 quantified training load in English Premier League soccer players (n=12) during one, two and three game weekly micro-cycles of the 2013-2014 season. Study 1 identified soccer training being significantly less than match play and identified that soccer training displayed evidence of training periodisation. Having identified typical training load during the weekly micro-cycle, it was recognised that soccer match play comprises a large portion of the weekly physical load. Accordingly, Study 2 quantified differences in season long physical load (inclusive of both training and match play) between players who were classified as starters (n=8, started ≥60% of games), fringe players (n=7, started 30-60% of games) and non-starters (n=4, started < 30% of games). Study 2 identified that unlike total seasonal volume of training (i.e. total distance and duration), seasonal high-intensity loading patterns are dependent on players’ match starting status thereby having potential implications for training programme design and prescription of player-specific nutritional guidelines. Additionally, daily energy expenditures (EE) and energy intakes (EI) of elite players are also not currently known. Therefore, studies 3, 4 and 5 quantified EE and EI in English Premier League soccer players consisting of outfield positions (n=6), a professional GK (n=1) and a player undergoing a rehabilitation period from an ACL reconstruction (n=1), respectively. Studies 3 and 4 were conducted over a 7-day period of the 2015-2016 season, consisting of two match days (MD) and five training days (TD). Study 5 consisted of six training days and one day off. Studies 3 and 4 identified CHO periodisation strategies employed by English Premier League Players such that CHO intake was greater on MD than TD. Additionally, players readily achieve current guidelines for daily protein and fat intakes, although energy and macronutrient intakes are skewed on TD. Study 4 also identified that the GK exceeded average daily EE with EI although he failed to meet current recommendations for meals on MD. In study 5 the player was operating in an energy deficit and he was able to decrease his total body mass in the initial 1-6 weeks post injury, which was attributable to largely fat loss. In summary, the work undertaken in this thesis has quantified the typical physical loading patterns of professional soccer players according to fixture schedule, starting status and in special populations. Additionally, the quantification of EI and EE (using DLW) also provides the first report of EE in elite soccer players from the English Premier League. When taken together, these data therefore provide a theoretical framework for soccer-specific nutritional guidelines especially in relation to the concept of nutritional (specifically, carbohydrate) periodisation. Further studies are now required to quantify the specific energy and CHO cost of habitual training sessions completed by elite soccer players as well as examining the manipulation of CHO availability on soccer-specific training adaptations.

Maintenance of blood glucose control and psychological well being are both important health outcomes for children with Type I diabetes. Diabetes management, the balance of insulin, diet and exercise, interacts with all aspects of these children's health, however, to date the effects of exercise in this interaction are poorly understood. This is particularly so with regard to the effects of exercise on psychological health. The aims of the present study were to investigate the effects of physical activity and fitness on the psychological and physiological health of children with Type I diabetes. The hypotheses were 1) that higher levels of physical activity and fitness would be positively associated with both greater psychological well-being and lower HbA1c, 2) that increasing physical activity would increase psychological health and lower HbA1c. Participants were aged 9-15 years, diabetes duration more than 2 years. There were 39 participants in phase one. Physiological data collected were physical activity, aerobic fitness, sum of skinfolds, BMI and HbAjc. Psychological questionnaires used were the physical self perception profile for children, the self efficacy for diabetes scale and the diabetes quality of life for youths questionnaire. Physical self esteem and quality of life were significantly associated with both greater fitness and higher physical activity. There were no significant associations between HbAjc and either fitness or physical activity. Phase two was a randomised controlled trial to evaluate a 12 week physical activity intervention. Thirty-nine children were recruited to this phase, 27 experimental and 12 control, of these 14 experimental and 7 control children completed the study. Data were collected as in phase one. When differences between the groups at time I were taken into account the only significant effect of the intervention was an increase in the BMI of the experimental group. There were increases in the hypothesised direction for aerobic fitness, perceived sports competence and perceived condition competence. Skinfold thickness and self efficacy for diabetes decreased significantly in both groups, strength competence increased significantly in both groups. There was no significant effect on HbA,,. Sample size was small and therefore the results must be treated cautiously due to the possibility of Type 2 error. iii It was concluded that both physical activity and fitness showed positive associations with psychological variables but that a physical activity intervention programme did not lead to significant increases in these variables. It is suggested that an intervention programme that incorporated physical activity and an educational or cognitive component would have a greater effect on the outcomes studied.

Ageing is an inevitable process characterised by a progressive deterioration in the function of a number of organs and systems, ultimately reducing the individual's quality of life. Despite its obvious importance, our understanding of the basic age-related changes in cardiac function remains poor. In part because past studies, describing the changes in cardiac function with age, have not always adequately controlled for different lifestyles or superimposed diseases, while using less than complete measures of overall cardiac function and appropriate scaling models. The aim of this thesis was to determine the changes in overall cardiac function associated with healthy ageing, using the comprehensive, non-invasive method of cardiac power output (CPO). After identifying that CPO was not affected by circadian rhythms, 149 sedentary men and women (19-75 years) and 60 active men were investigated. All were free from cardiovascular diseases and medications. The findings indicated that healthy ageing, in all subject populations, was associated with an ~17% decline in CPOrest, ~15% in CPOmax, and ~14% in CR. Age for age, sedentary men had greater CPO values than women, both at rest (~19%) and at maximal exercise (~25%). In addition, cardiac function was greater in the active men, compared with age-matched, sedentary controls, with values ranging from 11-30% greater. It was also found that body composition had a significant impact on the interpretation of CPO data. For example, when scaled allometrically for fat free mass (FFMb), absolute sex-related differences in CPO disappeared, as did the age-related decline in CPOrest. Also, in women no age-related changes in CPOmax were found once normalised to FFMb even though in men, CPOmax and CR still declined with age. Clearly, how these data are normalised relative to body composition is crucial to the interpretation of the effects of ageing or an active lifestyle. These are novel findings and indicate that healthy ageing is associated with reductions in overall cardiac function, as represented by significant declines in CPOmax and CR in men, but not women. In addition, endurance training improved aerobic capacity while attenuating the changes in cardiac function.

No description available.

Resistance exercise has been a popular form of muscle strength development for sport participants. This type of exercise activates a wide variety of physiological mechanisms involved with the exercising of muscle. The aim of this thesis was to investigate responses to dietary supplementation on muscular strength and biochemical indices to resistance exercise in female subjects. Firstly, to determine the reliability of the isometric test designed, and the number of trials required to-obtain reproducible measurements of maximum voluntary isometric force and rate of force development. Secondly, to establish heavy resistance exercise volume and intensity to produce a fatigue effect of a 40% reduction in measured force variables. Thirdly, to determine the optimal recovery period required to overcome the effect of fatigue responses to heavy resistance exercise after ingesting carbohydrate supplement (CHO). Finally, to determine the effect of creatine supplementation (Cr) on fatigue and recovery responses after resistance exercise in female subjects. Study one (1. A): The objective of study one was to quantify for female subjects, maximum voluntary isometric contractions (MVC) and rate of force development (RFD) and to evaluate the repeatability (between-days) of measurements. The data showed a small systemic bias between days for both, right and left leg and showed good reliability between days for MVC (range 5.4% to 11.5%), (9.55% to 36.3%) and (5.8% to 11.4%) for both legs, right leg and left leg, respectively. The LOA for RFD showed good reliability between days for all conditions (range 0.1% to 7.4%). It was concluded that the average of 3 trials between days is satisfactory for the repeatability of MVC and RFD. Study one (1. B) This second part of study one was to determine if there was a fatiguing effect of the testing protocol and also to establish the fatigue effect of the heavy resistance exercise. The same subjects were used as in study IA, but with the fatigue effects of an exercise trial between sessions 2 and 3. Subjects performed three sets of six different resistance exercises involving the lower body at an intensity corresponding to 60% of 1- RM (8-10 repetitions). The LOA for MVC was 0.6%, 13.7%, and 6.7%, for both legs, right leg and left leg respectively, and for RFD was 0.3%, 4.4%, and 5.3% for both legs. It was concluded that using both legs for studying the MVC was more reliable than using one leg for within-day and between-days force measurements. Study 2: The objective of study two was to establish the heavy resistance exercise volume and intensity to produce a fatigue effect of a 40% reduction in measured force variables and to establish the fatigue and recovery responses over a 48 hour period. Subjects were familiarised with the same testing procedures as in the pilot study 1B. All subjects performed three sets of six different exercises (lying leg curls, dumbbell lunges, barbell squats, leg extensions, straight leg deadlift, leg presses) at an intensity corresponding to 70% of 1-RM (8-10 repetitions). Measurements were obtained after 2h, 24h and 48h recovery for MVC and RFD. A significant main effect was found for time on MVC and RFD for both legs and the dominant leg (P < 0.001) across recovery time, but there was no significant difference for MVC at 48h for both legs and 24h, 48h for the dominant leg, and no significant difference for RFD between pre-exercise and 24h and 48h for the dominant leg. The fatigue protocol reduced measured force variables by 23.7% and 34.2%, and recovery from fatigue had been achieved after 48 hours. Study 3: The objective was to quantify the effect of carbohydrate supplementation on muscular strength after resistance exercise in females. Carbohydrate (CHO) supplementation and placebo trials were randomised and conducted at the same time of day (9: 00 am), on two separate occasions with one week between sessions. For the CHO trial, participants ingested a carbohydrate solution (0.5g CHO per kg/BM). The resistance exercise protocol described in study 2 was employed in this experiment. Instead of using 70% of the 1-RM, a work load in this study corresponding to 80% 1-RM was used. A significant (P < 0.05) overall main effect for condition and time on MVC and RFD was found, but there was a non-significant interaction between condition and time. The data showed that there was a faster recovery in the CHO condition with a suggestion of supercompensation. The resistance exercise for the lower body resulted in a significant decrease (P < 0.05) in MVC immediately after resistance exercise, and this occurred similarly in both CHO and placebo trials. Study 4: The objective was to quantity the effect of creatine (Cr) supplementation on muscular strength and biochemical responses to resistance exercise in female subjects. The methodological studies described in the pilot and main studies were use to create the protocols to reliably assess MVC and RFD. Subjects undertook a resistance exercise session at an intensity corresponding to 80% of 1-RM. They were required to consume 20g of creatine monohydrate or placebo in a double-blind experimental design for 5 days before being-tested. Blood samples were taken before each session of tests, and analyzed for blood biochemical variables which included: creatine kinase (CK), growth hormone (GH), Myoglobin (MYO). A significant effect of Cr was found on MVC and RFD recovery (P < 0.01). Body mass was not significantly different between sessions (P = 0.14) but there was a slight increase (1.0 kg) following Cr supplementation compared to other conditions. The CK and MYO, data revealed no significant main effect on time and conditions (P > 0.05). Indicating that the fatigue protocol did not induce muscle damage the GH data showed a significant mean effect of time and conditions (P<0.05), conforming an hormonal response to exercise. It was concluded that oral creatine supplementation enhances recovery following a resistance exercise challenge with a suggestion of a super-compensation at 48 hours. In summary, the procedure of resistance exercise was used in the four experimental studies and nutritional supplementation (CHO and Cr) significantly reduced the decline in maximal peak force and enhanced recovery following resistance exercise. It was concluded that the recovery from heavy resistance exercise in female appears to be aided by dietary supplementation producing an increase in the recovery of both maximal voluntary contraction force and rate of force development.

In recent years the prevalence of obesity, physical inactivity, sedentary behaviour and low cardiorespiratory fitness in Western countries has increased rapidly. These variables are independently associated with cardiovascular disease risk and/or mortality. Atherosclerosis begins in childhood and endothelial dysfunction is its earliest detectable manifestation. Endothelial dys/function can be quantified using flow mediated dilation (FMD). The primary aim of this thesis was to investigate childhood associations between endothelial function and a range of modifiable and non-modifiable CV risk factors. We sought to provide novel information regarding relationships between physical activity, sedentary behaviour, body composition, cardiorespiratory fitness and the heritability of endothelial function. In addition, we sought to explore the issue of the scaling of vascular outcomes for body size and composition. Study one (Chapter 4) addressed the question of scaling, by evaluating the efficacy of scaling vascular dimensions and FMD for different body composition variables using allometric and ratio procedures, with the aim of producing size independent vascular indices. Our data indicate that, if between-group comparisons of baseline brachial artery diameter are to be undertaken, appropriate, allometric scaling for measures of lean or total mass may need to be adopted. The application of such scaling to FMD data is debatable as the associations between FMD and body composition variables were very weak. We therefore concluded that the adoption of scaling FMD for body composition variables cannot be advocated until further research has been undertaken. Studies 2 and 4 (Chapters 5 and 7) assessed cross-sectional relationships between FMD and modifiable CV risk factors in young people. We examined associations between FMD and objective measurements of body composition, cardiorespiratory fitness, physical activity levels and sedentary behaviour. We observed a weak association between percentage body fat and FMD and no further relationships across cohort. However, depressed endothelial function was significantly related to, and predicted by high intensity physical activity. The relationship between FMD and high intensity PA was further reinforced by the findings from studies 3 and 4 (Chapters 6 and 7), which aimed to address the issue of seasonal variation in FMD and determine its predictors. The studies demonstrated that seasonal decline in vascular function was associated with, and predicted by, a change in high intensity PA but no other variables. These findings demonstrate, for the first time, that high-intensity PA may be an important determinant of vascular dys/function in children. The ramifications of these findings are that interventions aimed at improving vascular health in children may need to be refocused to bring about a progressive increase in physical activity, specifically high intensity physical activity, rather than reducing obesity or sedentary time per se. Finally, studies 5 and 6 (Chapters 8 and 9) utilised a classic twin study design to explore the role of genetics in the modulation of FMD. Through the comparison of intra-twin pair differences in mono- and di-zygotic twins, we were able to provide information relating to the genetic influence on FMD and calculate a heritability estimate. We concluded that, although a one-off measurement of endothelial function is under some level of genetic control, environmental factors may have a larger influence in the determination of FMD in young people (study 5).In study 6, twins undertook 8 weeks of aerobic exercise training. In this study, intra-twin differences in the adaptation of FMD were compared to changes in other variables. The results highlighted a greater similarity between MZ twins than DZ twins in the change in FMD, suggesting that exercise-induced improvements in FMD may be highly genetically determined. Taken together, the findings of this thesis infer that, whilst a genetic predisposition to endothelial dysfunction may exist, interventions that aim to increase high intensity physical activity have the potential to enhance vascular health in young people at risk of endothelial impairment and future development of atherosclerotic diseases.

It is well-established that turning on the spot or changing the direction of walking involves a stereotyped sequence of eye, head and body segment rotation characterized by an anticipatory gaze strategy driven primarily by eye movements (nystagmus). However, the relationship between eye movements and whole-body coordination during turning has not been fully explored under different environmental and sensory contexts and as a result, the neural mechanisms responsible for this coordination are poorly understood. The first aim of this thesis was to investigate the effects of turn size and speed on eye movements and intersegmental coordination. Results showed systematic relationships between turn speed, amplitude and eye and whole-body coordination characteristics and that the timing of eye, head and axial segment reorientation onset does not accurately represent coordination during the turn. Secondly, we investigated the effects of either removing vision or suppressing eye movements during turns. We found that eye and motor behaviour during vision removal was similar to behaviour during full vision, however suppressing eye movements delayed gait initiation and decreased stepping frequency throughout the turn. Next we examined the influence of neck muscle vibration on turning and found that stimulating neck proprioceptors to evoke the CNS perception of head rotation with respect to the upper body resulted in early turn initiation. Lastly, we looked at the effects of divided attention using a secondary cognitive task during the turn. We found that turn onset was delayed during dual-tasking, but eye and body coordination were unaffected. We conclude that oculomotor nystagmus during turning represents a crucial component of an automatic, subcortically generated motor synergy, the release of which is dependent on cortical and sensory input (i.e. eye and neck proprioception). We propose that turning on-the-spot is organized centrally as part of a whole-body gaze shift rather than a specialized adaptation to conventional locomotion.

In this thesis, two concepts concerning conditions of practice were examined for the practice, retention and transfer of perceptual-cognitive skill, specifically anticipation in tennis. First, from the motor skills literature, the contextual interference (CI) effect was investigated for the first time in perceptual-cognitive skill training. A blocked and random schedule of practice was used to train anticipation skills in tennis using video simulation techniques with transfer of learning assessed using a field-based task. Results showed support for the CI effect in this new domain as random practice had significantly greater response accuracy in the retention test, and significantly reduced decision time in the field-based transfer test, when compared to the blocked group. Subsequently, the underpinning mechanisms of the CI effect were examined focusing on cognitive effort and error processing. Across two experiments results showed that following errors, the random groups exhibited greater cognitive effort compared to errorless trials, whereas the blocked groups showed no difference between errorless and error trials. These results provided an alternative account for the CI effect by suggesting that it is not solely the switching of the tasks during random practice, but the role of error processing in conjunction with the switching tasks that result in greater cognitive effort and the CI effect. Second, the role of contextual information in perceptual-cognitive skills training was examined. Tennis shots were displayed to participants in either a smart-random structure, which showed shots in a tactically relevant manner, or in a random order so that no contextual information was available, just postural cue information. The smart-random structure group showed superior response accuracy in retention and reduced decision time in a field-based transfer test. Results demonstrated the benefits of contextual information for the retention and transfer of perceptual-cognitive skills in tennis. The overall findings extend the research in perceptual-cognitive skill training and have several theoretical and applied implications.