The trainability of youth at specific periods during growth and maturation has become a key issue in paediatric exercise science. The development of physical capacities such as movement speed, strength and power is difficult to predict in youth meaning that the structuring of training can be a significant challenge for coaches. Accordingly, methodologically sound research is required to underpin a more informed approach to the formulation of programmes of physical development. To this end, the purpose of this work was to investigate the trainability of youth athletes at specific stages during maturation (pre-, mid-, and post-peak height velocity) by addressing some of the shortcomings of the existing body of literature. Short-term controlled interventions were undertaken and they extended from the findings of three meta-analytical reviews, all of which examined the effect of training on the development of speed, strength and power in youths aged 9 to 18. These investigations were focused on the manipulation of modifiable factors, such as the training stimulus, as opposed to non-modifiable factors, such as maturity (which was generally controlled for). With some exceptions, which are potentially explainable, speed, strength and power were, on the whole, more trainable in youths as they advanced in maturation with the mid-peak height velocity phase being a particularly important time for the development of these capacities. This could indicate the presence of a maturational threshold which moderates responses to training but this can also be coincident with a period of impaired performance potentially related to reduced motor control due to rapid growth rates. Because of the way speed, strength and power can develop in youth athletes, the pre-peak height velocity phase of development may be more conducive to neuromuscular training with a coordinative component which establishes the movement competency required for more advanced techniques. An intensification of resistance (strength) training can be of benefit during mid-peak height velocity though impaired movement or a higher susceptibility to injury could compel coaches to reduce sprint (speed) and/or plyometric (power) training at this time. During the post-peak height velocity phase, athletes can be transitioned to more advanced training techniques, that are traditionally used with adults, if they possess the necessary coordination and experience to do so. Regardless of the results in this work, at every stage of development it is important for coaches to make programming decisions for youth athletes based, primarily, on training age and movement competency with the above maturity-related recommendations being suitable for those who have been exposed to high quality training from an early age.

The aim of this series of studies was to determine the effect of power clean variation (power clean (PC), hang power clean (HPC), mid-thigh power clean (MTPC) and mid-thigh clean pull (MTCP)) and load on force time characteristics, in an attempt to identify the optimal variation and load to develop specific force time characteristics. Study 1 demonstrated that assessment of peak force, peak rate of force development (RFD) and peak power were highly reliable (ICC r≥0.968) during the PC, with smallest detectable differences of ≥8.68 N, ≥24.54 N.s, ≥68.01 W, respectively, signifying a meaningful change. Study 2 and 3 demonstrate that the MTCP and MTPC are preferential in terms of maximising acute kinetic performances when compared to the PC and HPC, as they result in the greatest peak force, peak RFD and peak power. In contrast, study 4 showed no kinetic differences (p > 0.05) across PC variations (PC, HPC, MTPC) or load (70, 70, 80% 1-RM) in inexperienced female collegiate athletes. Study 5 revealed that peak power output during the PC was achieved at a load of 70% 1-RM, although this was not significantly (p > 0.05) different when compared to the 60% and 80% 1-RM loading conditions, in inexperienced athletes, in line with previous research in well trained athletes. Finally, study 6 demonstrated that when the MTCP is performed with loads of 120-140% 1-RM PC, significantly greater peak force (p < 0.001), peak RFD (p=0.004) and impulse (p≤0.023) occur when compared to loads ≤100% 1-RM. In contrast, significantly greater peak power (p≤0.02), bar displacement (p≤0.02) and bar velocity (p < 0.001) occurs when performed at a load of 40-60% 1-RM. When incorporating the MTCP into different training mesocycles, it would be useful to use heavier loads during the strength phases, progressing from 120-140% 1-RM PC, to maximise force production and RFD. In contrast, during power mesocycles, it would be advantageous to progressively reducing load to 40-60% 1-RM PC, to elicit the greatest peak power possible during the MTCP or MTPC.

Exercise is inherently linked with the production of reactive oxygen and nitrogen species (RONS) resulting in augmented oxidative stress post-exercise. Antioxidant supplements have been proposed to reduce exercise-induced oxidative stress, but this alleviation can potentially negate signalling pathways mediated by RONS. This thesis presents novel findings on the consumption of antioxidant supplements and the effects of habitual supplementation on exercise-induced oxidative stress following a cycling sportive in recreational cyclists (chapters 1 and 2). Consumption of antioxidant supplements is not associated with age, cycling experience or weekly training hours; nor do they provide additional protection in reducing oxidative stress on completion of a cycling sportive. The final two experimental chapters assessed the effect of habitual supplementation on basal levels of endogenous antioxidants and the oxidative stress response to steady-state cycling (chapter 4). And the effect of polyphenol supplementation on cycling recovery, assessed by markers of oxidative stress, inflammation and cycling performance in trained cyclists (chapter 5). Habitual supplementation did not affect baseline concentrations of superoxide dismutase-1 (SOD1), superoxide dismutase-2 (SOD2) or glutathione peroxidase-1 (GPx-1); nor the oxidative stress response to steady-state cycling. Supplementation with a polyphenol drink did not attenuate exercise-induced oxidative stress, inflammation, or improve cycling performance compared to placebo.

Increasing fat oxidation rates during exercise may be beneficial for the athletic population. At rest, ingestion of Green Tea Extract (GTE) has been found to augment fat oxidation, but there are limited data on the effects during exercise. This thesis systematically investigated the effects of GTE ingestion on exercise metabolism in physically active males. We set out to determine if longer-term feeding of GTE could increase fat oxidation rates during a steady state exercise bout to a greater degree than an acute dose. However, irrespective of the length of ingestion no measureable change in substrate metabolism was found. Due to the large individual differences in fat oxidation at a given absolute and relative exercise intensity, we investigated the effects of acute GTE ingestion during a graded exercise test. Again, no change in fat metabolism was found over a wide range of exercise intensities. Finally, we collected fat oxidation data from a large cohort of athletes. From these data we set new criteria to define individuals as either a fat or carbohydrate metabolic type. Although it is still not known fully what determines metabolic type, the use of a nutritional intervention may be more effective in one type over the other.

South Asian (SA) women in the United Kingdom (UK) are disproportionately affected by chronic diseases and inactivity. However, there is limited published research documenting PA/ST among SA women. The purpose of this PhD research is to employ a mixed methods design to quantify PA/ST among SA women in the UK, assess validity of common methods of PA/ST data collection and to provide a better understanding of the factors that may influence PA/ST in this group. Methods: 140 SA women wore an accelerometer and 36% (n=50) of the sample completed the International Physical Activity Questionnaire (IPAQ). 17% (n=24) of the sample participated in semi-structured interviews. Results: SA women are engaging in similar amounts of PA/ST as the general UK population. IPAQ data underestimated PA/ST when compared to objective data. There were no significant correlations between measurements of the two methods. SA women had difficulty understanding the terminology, content and context of the IPAQ, and difficulty recalling ST.

The aim of this thesis was to investigate appetite responses to exercise in highly-trained endurance athletes and to assess the effect of different exercise characteristics in mediating these responses. Chapter 3 introduce a novel tool – The Visual Meal Creator – that is shown to be a valid measure of subjective appetite and may prove a strong predictor of food intake. Chapters 4 and 5 demonstrate that an exercise-induced suppression of appetite is experienced in highly-trained athletes, although there does appear a blunting to this response. It may be that an elevated fitness level, resulting in reduced physiological and metabolic perturbations during exercise mediates this blunting. Any exercise-induced appetite suppression response would appear independent of the duration, or energy cost of exercise. This is partly supported by findings of Chapter 6: a suppression of appetite after very-low volume sprint interval cycling exercise in overweight and obese individuals. In no instance was a suppression enduring and feeding was not influenced by exercise in any study of this thesis. The responses to exercise of appetite-associated hormones were also investigated throughout Chapters 4 to 6. Acylated ghrelin and GLP-1 exhibited profound, anorexigenic responses to high-intensity exercise, with the GLP-1 response exhibiting some degree of duration or energy cost dependency. However, there appeared a dissociation between changes in appetite-associated hormone concentration and changes in both subjective appetite and energy intake. This questions the well-held belief of the importance of appetite-associated hormones in mediating post-exercise appetite regulation.

Cold water immersion is commonly used to alleviate the stress and damage that ensues following strenuous exercise. Alongside its purported performance and analgesic benefits recent literature highlights the positive impact it may have towards endurance adaptive responses, particularly on key markers of mitochondrial biogenesis. Despite these recent advances showing PGC-1α, the ‘master regulator’ of mitochondrial biogenesis, being augmented in its post-exercise response by cold water immersion, the precise controlling mechanisms remain to be determined. However, it has been suggested that local cooling effects on AMPK and p38 MAPK related signalling and/or increased systemic β-adrenergic stimulation are involved. Study 1 (Chapter 4) examined whether post-exercise cold-water immersion induced augmentation of PGC-1α mRNA is mediated through local or systemic mechanisms. Participants completed acute cycling followed by seated-rest (CON) or single-leg cold-water immersion (CWI; 10 min, 8°C) with muscle biopsies obtained pre-, post- and 3 h post-exercise from a single limb in the CON condition but from both limbs in CWI (thereby providing tissue from a CWI and non-immersed limb, NOT). Muscle temperature decreased following CWI (-5°C), with lesser changes observed in CON and NOT (-3°C; P<0.05). A significant interaction effect was present for AMPK phosphorylation (P=0.031). Exercise (CON) increased gene expression of PGC-1α 3 h post-exercise (~5-fold; P<0.001). Post-exercise CWI augmented PGC-1α expression above CON in immersed (CWI; ~9-fold; P=0.003) and NOT limbs (~12-fold; P=0.001). Plasma Normetanephrine concentration was higher in CWI vs. CON post-immersion (860 vs. 665 pmol·L-1; P=0.034). Data herein reports for the first time that local cooling of the immersed limb evokes transcriptional control of PGC1-α in the non-immersed limb, suggesting increased systemic β-adrenergic activation of AMPK may mediate, in part, post-exercise cold-induction of PGC-1α mRNA. Study 2 (Chapter 5) assessed the impact of combining a post-exercise cooling stimulus with prior low glycogen as both stressors are shown to separately enhance the post-exercise PGC-1α response. A single-leg depletion protocol and bi-lateral muscle biopsies with and without post-exercise CWI were utilised to give the following conditions: High glycogen control (HI CON), Low glycogen control (LO CON), High glycogen CWI (HI CWI) and Low glycogen CWI (LO CWI). HI limbs began the experimental day ~190 mmol·kg-1dry weight (dw) with low limbs at ~85 mmol·kg-1dw glycogen before undergoing the same relative exercise protocol as Chapter 4. PGC-1α mRNA was different between conditions (P = 0.039) with HI glycogen limbs showing greater expression than contralateral LO glycogen limbs (P < 0.05). PGC-1α mRNA increased to a greater extent in CWI HI vs. CON HI (ES 0.67 Large). Data herein supports previous research that shows post-exercise CWI is able to augment PGC-1α above the exercise response alone, however this response was not evident in heavily depleted limbs (~85 mmol·kg-1dw), suggesting a critical threshold may exist for the expected enhancement of PGC-1α to occur when exercise is commenced in a low glycogen state. Chapter 6 sought to examine the contribution of CWI (Chapter 4, Experiment 1) and/or low muscle glycogen (Chapter 5, Experiment 2) in the activation of PGC-1α via either the canonical (Exon 1a) or the alternative promoter (Exon 1b) regions. Data was obtained using muscle biopsy samples collected from the previous chapters (Chapter 4 and 5). Exercise increased the expression of promoter specific PGC-1α, with greater fold changes seen in Exon 1b. Experiment 1 (Chapter 4) showed PGC-1α Exon 1b expression closely matched the pattern of expression seen for total-PGC-1α, with large, systemic cold-induced increases in the non-immersed (NOT, 2344 fold change from Pre, P = 0.010) and immersed (CWI, 1860 fold change from Pre, P = 0.07), compared with the control limb (CON, 579 fold change from Pre). Results from experiment 2 (Chapter 5) saw PGC-1α Exon 1a and 1b gene expression increase post-exercise, with the Exon 1b response showing lower fold-changes at 3h post-exercise compared to those from Experiment 1 (chapter 4), despite the same exercise protocol being utilised (~200 fold increases in experiment 2 vs. ~2000 fold increases in experiment 1). The data suggests that depletion exercise in the days prior to the experimental day may have raised basal RNA levels, which may have therefore contributed to dampened fold-changes seen post-exercise when relativized to pre-exercise values. The lack of a cold augmentation in promoter specific PGC-1α gene expression in experiment 2 suggests this response may be extremely acute, and may not occur when cooling is undertaken on the third day of exercise. This thesis provides a novel insight into the influence of local, systemic and upstream activating mechanisms regulating the post-exercise, post-cooling and exercising in low glycogen states upon PGC-1α. These findings provide mechanistic application for future study designs and practical application in the support for the use of CWI when the intended target is an upregulation of the gene PGC-1α.

Youth sport has been advocated as a vehicle through which more physically active lifestyles can be encouraged among children and adolescents. Employing objective assessments of physical activity (PA), the purpose of this thesis was to investigate the value of youth sport as a context for PA promotion and obesity prevention. Results from Study 1 indicated 37% of youth sport football participants did not meet recommended levels of moderate-to-vigorous PA (MVPA) during their youth sport engagement. Study 2 demonstrated negative associations between daily PA levels of grassroots footballers and obesity linked health outcomes, with the reverse true for sedentary time (ST). Guided by self-determination theory (Deci & Ryan, 1987), findings from Studies 3 and 4 revealed perceptions of coach provided autonomy support were positively associated with sport related autonomous motivation, and in turn, higher MVPA participation (daily MVPA as well as PA accrued during youth sport) and lower ST. This thesis underlines the value of youth sport as a setting through which levels of PA can be increased, and ST reduced among youth. Research described within also points to the important role of the coach-created environment and player motivation in predicting variability in PA engagement and ST among young grassroots footballers.

The overall aim of this thesis was to investigate modalities used as components of pre event/training preparation, to try to develop an optimal preparation strategy for sports performers. It concentrates on the stretch modalities commonly used by athletes as part of a warm-up designed to prepare them for subsequent performance. Past literature suggests that static stretching as part of a warm-up leads to a decrease in performance when compared to an active warm-up or a warm-up including dynamic stretches. Not surprisingly this has led to a movement away from static to dynamic stretches by many athletes. The presented publications were conducted to clarify a number of issues raised by past research studies. A lack of ecologically valid studies is apparent; the static stretch protocols used in most of the early research in this area has failed to explore what sports performers actually use as part of their training, while there was a lack of research examining the effect of dynamic stretches on performance. Of particular relevance is the lack of research looking at the mechanisms behind the changes in performance linked to warm-ups incorporating dynamic stretches. Therefore, this group of publications attempts to systematically examine the effects on performance of manipulating the stretch component of an active warm-up, while exploring the potential mechanisms linked to any changes in performance. The general findings of this series of papers provides evidence that static stretches, as part of an active warm-up, are linked to a decrease in the acute performance of a range of physical capabilities; including sprint, agility, jump and maximal force output. The mechanisms behind these performance changes are multifaceted, with decreases in core temperature and heart rate, decreases in musculotendinous unit stiffness and a decrease in muscular activity, when compared to a general active warm-up established. In contrast when a dynamic stretch replaces the static stretch component and is incorporated within a warm-up, performance is enhanced when compared to an active warm-up. The mechanisms behind this seem to be less temperature related and more closely linked to the neuro-muscular system. Greater muscular activity is linked to dynamic stretches, causing an increase in peak force and rate of force development, compared to an active warm-up protocol. This effect seems to be enhanced the faster and more specific the dynamic stretches are to the chosen performance measure, while combining static stretches with dynamic stretches as part of a preparation strategy still leads to decreases in performance compared to an active warm-up combined with dynamic stretches. In conclusion, to maximise acute maximal performance in sports specific motor skills, an active warm-up combined with specific dynamic stretches is recommended to sports performers and coaches.

The use of solutions containing creatine and glycerol (Cr/Gly) has become popular amongst athletes as a means of hyperhydrating prior to exercise in the heat, since achieving an optimal hydration status appears to be a critical factor for temperature and cardiovascular regulation during exercise in the heat. Hyperhydration has previously been achieved by means of a pre-exercise water loading strategy with the use of hydrating agents (i.e., Cr and Gly) in combination. Certain problems are related to this hyperhydration strategy and are investigated in this thesis. Firstly, the use of Gly has been prohibited and added to the WADA banned list due to the potential of Gly plasma expansion properties, to mask the use of doping substances such as erythropoietin stimulants. However, the scientific basis of the inclusion of Gly as a “masking agent” remains inconclusive. Secondly, the addition of high CHO amounts to the Cr/Gly strategy is central to successful Cr uptake and subsequent hyperhydration. Thirdly, high CHO intake has been linked to high plasma TAG in the athletic population and partial replacement of CHO with insulinotropic agents, such as alpha lipoic acid (Ala), a natural antioxidant and co-factor in the pyruvate dehydrogenase complex, has been shown to enhance Cr uptake under conditions of reduced CHO. On a separate note, Cr and Ala have been found to individually improve Glu tolerance and lipid markers in sedentary individuals while the combined effects of Cr/Ala supplementation on Glu tolerance and lipid markers of sedentary individuals have not been investigated. The aim of chapter 3 was to determine the effects of a hyperhydrating supplement containing 1.0 g/kg of BM of Gly, 10.0 g of Cr and 75.0 g of Gluon on doping-relevant blood parameters. This hyperhydration did not significantly alter PV or any of the doping-relevant blood parameters (e.g., Hct, [Hb], Ret (%) and tHb-mass). Due to the fact that most athletes, in situations where they may be subject to testing by WADA, may choose rapid hyperhydration protocols, the effects of a shorter supplementation 2 protocol on doping related blood parameters, was investigated in chapter 3. For this purpose, a separate cohort of participants consumed the Gly/Cr/Glu supplement over the course of one day. Despite a significant increase in BM over the course of supplementation lasting 8 hours, PV changes and the blood-relevant doping markers of interest were not significantly affected, even when urinary [Gly] was clearly above the urinary [Gly] observed following typical dietary Gly intake. In conclusion, this study showed that supplementation with a hyperhydrating solution containing Gly for 7 days or a short supplementation protocol lasting one day did not significantly alter doping- relevant blood parameters. The aim of chapter 4 was to determine whether Cr/Gly-induced thermoregulatory and cardiovascular responses are maintained when part of the Glu in the Cr/Gly supplement is replaced with the insulintropic agent Ala. Median and range values of TBW increased significantly by 2.1 (1.3-3.3) L and 1.8 (0.2-4.6) L in the Cr/Gly/Glu and Cr/Gly/Glu/Ala groups, respectively (P=0.03). During constant load exercise, HR and Tcore were significantly lower post-supplementation: HR was reduced on average by 3.3±2.1 beats/min and by 4.8±3.3 beats/minute (mean±S.D.) and Tcore by 0.2±0.1 (mean±S.D.) in the Cr/Gly/Glu and Cr/Gly/Glu/Ala groups, respectively. The reduction in HR and Tcore was not significantly different between the supplementation groups. In comparison to the established hyperhydrating Cr/Gly/Glu supplement, a supplement containing Cr/Gly/Ala and decreased amount of Glu provides equal improvements in thermoregulatory and cardiovascular responses during exercise in the heat. The aim of chapter 5 was to determine whether acutely increasing dietary CHO intake prior to endurance events, through the intake of hyperhydrating Cr/Gly solution enriched with Glu, leads to changes in plasma lipids of endurance trained cyclists and whether replacing part of the Glu within this supplement with an insulin potentiating agent, such as Ala, attenuates these changes. Fasting concentration of TAG increased significantly 3 (P<0.01) after supplementation with Cr/Gly/Glu (Pre, 0.9±0.2 mmol/L; Post, 1.3±0.4 mmol/L) and Cr/Gly/Glu/Ala (Pre, 0.8±0.2 mmol/L; Post 1.2±0.5 mmol/L) but the increase in plasma TAG concentration was not significantly different between the two groups. Supplementation had no effect on fasting concentration of total-, HDL-, and LDL- cholesterol and insulin resistance. The acute increase in dietary CHO intake during the 7 days of supplementation with Cr/Gly/Glu induces an increase in plasma TAG concentration that is not attenuated by partial replacement of CHO with Ala. The aim of chapter 6 was to determine whether Cr supplementation, in the absence of exercise would lead to improvements in Glu tolerance in healthy overweight sedentary males and if Cr supplementation combined with Ala, would improve Glu tolerance and plasma lipids in healthy overweight sedentary males. The purpose of this pilot study was to determine the efficacy of Cr and Cr/Ala combined supplementations in improving Glu tolerance, insulin sensitivity and lipid profile of healthy overweight sedentary males. A four-week supplementation with Cr improved Glu tolerance while supplementation with Cr/Ala failed to have such an effect. Nevertheless, supplementation with Cr/Ala for 4 weeks decreased LDL-cholesterol significantly. None of the other blood markers were significantly different following 4 weeks of supplementation with Cr or Cr/Ala. This study found that Cr improved Glu tolerance without any changes in insulin sensitivity or lipid profile of healthy overweight sedentary males, in the absence of exercise. Moreover, the addition of Ala to Cr, had no added effect on Glu uptake, insulin sensitivity or plasma lipids apart from LDL-cholesterol. However, a randomised control trial with a higher sample size, recruiting both experimental, and control groups should be carried out to confirm these findings.