Glucose transporter 4 (GLUT4) in skeletal muscle plays a vital role in the maintenance of glucose homeostasis. Chapter 2 of this thesis develops an immunofluorescence microscopy method to generate novel information in human skeletal muscle on the effect of physiological stimuli on GLUT4 localisation, translocation to the plasma membrane and total protein content. Chapter 3 shows that training-induced increases in total GLUT4 protein content are driven by increases in the number of large and size of smaller intracellular GLUT4 storage clusters in human skeletal muscle. In chapter 4 the method successfully demonstrates GLUT4 translocation 30 min following glucose ingestion and 30 min after the start of moderate intensity cycling exercise in humans. GLUT4 translocation after glucose ingestion is transient and modest in comparison to the exercise response. Chapters 5 and 6 report no changes in GLUT4 translocation following an 80 min hyperinsulinaemic-isoglycaemic clamp in rats and a 2 h hyperglycaemic clamp in humans despite elevated rates of whole body glucose disposal in both experiments. This immunofluorescence method will be a valuable analytical tool in future studies investigating the mechanisms behind changes in muscle glucose uptake in response to obesity, age-related chronic diseases and therapeutic interventions including diet and exercise.

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.

Focal adhesion kinase (FAK) and paxillin are proteins implicated in the mechanisms that link chronic alterations in mechanical force within skeletal muscle and its microvasculature to the functional adaptation seen with changes in physical activity. This thesis developed novel immunofluorescence microscopy methods to visualise and measure FAK and paxillin responses in human skeletal muscle and its microvasculature. Chapter 2 reveals high FAK protein content in the (sub)sarcolemma of skeletal muscle fibres and within the microvascular endothelial and vascular smooth muscle cell layers. Chapter 3 demonstrates that FAK protein content is increased at (sub)sarcolemmal and sarcoplasmic regions of skeletal muscle fibres and within the microvascular endothelium following 12 weeks resistance-type exercise training in elderly individuals. Chapter 4 shows that FAK and paxillin colocalise at the (sub)sarcolemma of skeletal muscle fibres and within the microvasculature. Chapter 5 demonstrates that FAK and paxillin are increased at the (sub)sarcolemma and within the microvascular endothelium following 6 weeks endurance- and resistance-type exercise training in young previously sedentary individuals. The novel data generated in this thesis, in combination with recent literature findings, support the hypothesis that FAK and paxillin play an important role in upstream mechanotransduction signals that control skeletal muscle fibre hypertrophy, mitochondrial biogenesis, insulin sensitivity, microvascular function and angiogenesis.

Maintenance of upright, human balance is neurologically and biomechanically a complex process, though the ankle strategy predominates in quiet standing. This investigation seeks insight into the complex problem by studying a reduced, yet related problem of how the ankle mechanisms are used to balance a human proportioned inverted pendulum. A distinguishing feature of the task is that despite one's best efforts to control this unstable load some irreducible sway always remains. Contrary to published ideas, modulation of effective ankle stiffness was not the way that sway size was altered. Rather, position was controlled by an intermittent, neurally modulated, ballistic-like pattern of torque whose anticipatory accuracy was improved to reduce sway size. Using a model, and by direct measurement, I found the intrinsic mechanical ankle stiffness will only partially counter the "gravitational spring". Since this stiffness was substantially constant and cannot be neurally modulated, I attribute it to the foot, tendon and aponeurosis rather than the activated calf muscle fibres. Thus triceps-surae muscles maintain balance via a spring-like element which is itself generally too compliant to provide even minimal stability. I hypothesise that balance is maintained by anticipatory, ballistic-like, biasing of the series-elastic element resulting from intermittent modulation of the triceps-surae.

Previous studies have shown that the intrinsic mechanical stiffness of the ankles is less than necessary to fully stabilize the body in the upright position (Loram and Lakie, 2002a; Morasso and Schieppati, 1999; Morasso and Sanguineti, 2002; Casadio et al., 2005). Following these studies, research about the controlling mechanisms of standing (the maintenance of an upright posture by a combination of intrinsic and active mechanisms) has developed considerably (Lakie et al., 2003; Loram et al., 2005a,b, 2011; Masani et al., 2006; Maurer and Peterka, 2005; Peterka, 2002). However, very little attention was given to the intrinsic mechanisms themselves. Here I tackled this issue by manipulating the ankle (and its surrounding tissues) in various ways. The objective was to investigate ankle stiffness dependency on mechanical properties that are particular to muscles and tendons. Within-individual differences were confirmed in various conditions. I have shown that in standing, intrinsic ankle stiffness is affected by movement amplitude and history of movement, as well as active ankle torque and passive tendon stretch. I have found no dependency of ankle stiffness on localized cooling. With regards to the effect that differences in intrinsic ankle stiffness may cause to standing sway, a between-individual analysis showed an inverse correlation between ankle stiffness and sway magnitude.

Soccer is the most widely played sport in the world. Consequently, players train and compete in a wide variety of environmental conditions. Professional soccer players normally train daily and compete once or twice a week. Exercise hot environments can lead to dehydration because sweat losses often exceed fluid intake. Sweat rate can range between 1 to 2.5 L.h-1 depending on factors such as environment conditions, fitness and clothing. Previous studies of soccer players have found that players are often dehydrated. This thesis consists of three studies conducted in Riyadh, Saudi Arabia. Young Saudi professional soccer players based at the Al Hilal club were recruited to the study. The author worked them during their training and matches at different periods during the year to study the effects of exercise in warm and cool conditions. Their hydration status was studied using a range of methods including analysis of the blood and urine. The main aims of these experiments were to examine the effect of exercise intensity in temperate and hot environments on blood, urine, core body temperature and aldosterone concentrations. The first study evaluated their hydration status over three days of training and one match in temperate conditions. The aim of this study was to establish that research could be conducted as players went through their normal routines determined by the club management and coaches. Change in body weight, serum osmolality and electrolytes, sweat loss, fluid intake and aldosterone concentrations were measured. The range of ambient temperatures was between 23.4 and 30.6 oC and the relative humidity ranged between 14.2 and 23.2 %. Eleven Saudi professional soccer players participated in this study. Their body weight significantly decreased during exercise. Serum osmolality was always high indicating dehydration. It increased significantly during match play, from pre 288 ± 3 mOsm/kg to 293 ± 4 mOsm/kg. Day by day changes of serum osmolality before training sessions and match were small and on some days statistically significant. Plasma aldosterone concentrations significantly increased after the match. The magnitude of dehydration was affected by the intensity of the training sessions GPS was used to measure distance covered. Players covered more distance in match play (7326 m) than in training sessions. Core body temperature was elevated during exercise but not to dangerous levels. The second study was aimed to repeat these measurements in the summer time during the early season in September. Again, three training sessions and one match were studied. The environment conditions were above 35 oC on all days and the relative humidity was between 10.5 and 13.0 %. The success of the first study in establishing a good relationship allowed some expansion and sixteen soccer players were recruited. Similar results were obtained and fluid losses were greater in the hotter conditions. None of the players replaced all of the fluid lost in training sessions or match play. The mean of sweat rate was 1932 ± 512 ml.h-1 and players dehydrated by 1.8 ± 0.7 % during match play. The serum sodium concentrations were small but statistically significant for some sessions. Similar changes were seen in serum osmolality. Estimated urine osmolality and specific gravity values were high on all days. Plasma aldosterone concentrations increased significantly during two training sessions and match play. On all days the mean of core temperature during exercise increased significantly. The third study aimed to improve hydration in a group of players before they started training. Responses were compared in hydration intervention (HI) and hydration control (HC) groups. Each group comprised of eight soccer players. The ambient temperature during this study was about 29 oC. Measurements were taken on three days; the first day was as base line. Next two days, intervention group were instructed to consume 500 ml before attending the club. Independent t-test showed no significant differences between the two groups in base line of age, body weight, height and BMI (P > 0.05). Blood, urine, intensity of exercise, aldosterone and core body temperature were measured between groups. Serum electrolyte concentrations were not different in the two groups on three days. The serum osmolality of HI was significantly lower than HC before training two (T2) during the study (P < 0.05). No differences in fluid intake were observed during training and sweat rate and loss did not differ during training sessions in the two groups. In addition, serum osmolality did not change after T2 in HI, where the control group had significant increase in osmolality after this training session (P < 0.05). On the third day, serum osmolality did not differ between the two groups. However, after exercise serum osmolality elevated from pre to post exercise. The HI group had lower aldosterone concentrations before T2 started than HC group (P < 0.05). The core temperatures rose during exercise in both groups and there were no differences between the two groups. In conclusion, the three studies were completed successfully. Good data were obtained and it was possible to conduct research with the players as they followed their normal routines of training and playing. These data showed that the players were dehydrated before and during training and match play. Sweat loss was greater in hot conditions than in temperate conditions. Serum osmolality elevated after exercise in hot and temperate conditions and by different intensity of exercise. Plasma aldosterone concentrations were affected by the exercise in all studies.

Pacing research attempts to explain how effort varies during athletic events to produce the best performance without premature fatigue. Little is understood about the cognitive processes leading to pacing decisions and behaviour. The aim of this thesis was to measure cyclists’ visual behaviour, using eye-trackers, to determine information acquisition patterns during cycling time trials (TT). The first study found experts looked at primary information longer than novices during 10 mile TTs, with speed being the primary information source for experts, and distance was the primary information source for novices. A follow-up study confirmed that speed was the preferred source of information for experienced cyclists, and that pacing and performance decrements were observed when removing preferred information sources. In a third experiment, it was found that limiting the availability of preferred information to 15 sec every 10% and 20% of a 5 km TT, had no effect on performance compared to continuously available preferred information. In a final study an attempt was made to measure cyclists’ visual behaviour during a road time trial because the laboratory studies are limited by ignoring balance, navigation and collision avoidance demands on visual attention. It was found that cyclists were looking at the road for an average of above 50% of over all time. Cyclists spent approximately 20% of the overall time seeking performance information, in which 7/10 chose speed as the primary information. It is concluded that difference in information acquisition processes exist between novice and expert cyclists with experts affording more attention to speed and novice to distance. Furthermore, performance remains relatively unaffected by limiting the availability of preferred feedback information, which may be important so that during road-based TT’s, the capacity to attend to balance, navigation and collision-avoidance cues exist.

Although habitual exercise can have profound beneficial effects on the cardiovascular system there is a growing evidence base to suggest that single acute bouts of endurance exercise can lead to the release of cardiac biomarkers of damage and dysfunction. Whether this cardiac biomarker release is indicative of reversible or irreversible cardiomyocyte damage is not clear. The first study in this thesis employed a new high sensitivity assay to assess cardiac troponin (hs-cTnI) as well as N terminal pro-brain natriuretic peptide (NT-proBNP) before, during and after 2 hr of treadmill exercise in young, healthy but non-athletic participants. No hs-cTnI samples were elevated above the detection limit of the assay during exercise and only one participant had a detectable hs-cTnI value post-exercise (22 ng/L). NT-proBNP levels were elevated more consistently during exercise and recovery. In the second study the repeatability of cardiac biomarker responses to 2 hr of treadmill exercise was assessed 1 and 12 weeks after an initial trial (Study 1). The same participant had an elevated hs-cTnI value post-exercise in week 0 (22ng/L) and week 1 (30 ng/L). All other participants had no detectable hs-cTn in trials in week 0 and 1. At week 12 one participant (different to the person in week 0 and 1) had elevated hs-cTnI post-exercise (25 and 38 ng/l). NT-proBNP levels rose with exercise in all trials but peaked earlier in trial 1 and demonstrated great individual variability. Study 3 and 4 investigated the role that ischemia may play in cardiac biomarker release and cardiac functional changes after endurance exercise. Ischemia was studied indirectly by employing remote ischemic preconditioning (RIPC) in a single-blind cross-over research design. In study 3 trained cyclists completed 2 one hour time trials in a controlled laboratory environment with trials preceded immediately RIPC or a SHAM protocol. Hs-cTnI values were reduced after the RIPC trial compared to the SHAM during recovery from exercise (significant main effect for trial). NT-proBNP and indices of cardiac function were not mediated by RIPC. Using the same RIPC intervention in study 4 we employed a longer exercise task (160 km cycle) in trained cyclists. We confirmed a partial attenuation of hs-cTnI appearance post-exercise following the RIPC intervention compared to the SHAM. In addition NT-proBNP was lower after the RIPC trial but RIPC did not mediate any change in cardiac function post-exercise. These data reflect the first tentative evidence that ischaemia could be implicated in post-exercise cardiac biomarker release. Although exercise can lead to cardiac biomarker appearance, and ischaemia may be implicated mechanistically, the rapid appearance and removal of these biomarkers as well as the limited impact on cardiac function still supports a reversible insult to the cardiomyocytes.

It is becoming accepted that exercise increases gastrointestinal (GI) symptomology and permeability potentially effecting performance and recovery. This thesis addresses the issues of how exercise intensity, modality and pattern of exercise will impact upon GI permeability, damage and symptomology expression. Further it will examine how these factors may be modified by the environmental conditions under which they take place and by the use of pharmacological agents. In study 1 chapter 4, six male soccer players undertook both a 90-min rest or soccer specific intermittent exercise protocol (SSIE) under two environmental conditions (Hot 32°C or Cold 12°C) to evaluate how GI permeability and symptomology was affected by simulated soccer match play activity. SSIE elevated GI permeability relative to rest in both hot and cold conditions but these changes were only significant in the protocols undertaken in the heat. Such differences potentially reflecting the attenuated exercise intensity elicited by the protocol. However, exercise and rest in the heat relative to cold was associated with significantly higher GI permeability and wider array of subjective gastrointestinal symptomology. In study 2 chapter 5 the activity patterns typically experienced in soccer i.e. continuous and intermittent running were compared when 10 male participants undertook a series of protocol (s); rest, continuous steady state and intermittent exercise performed at the same ‘relative intensity’ of 70% V̇O 2 peak. Interaction with environmental stressors in the Hot 32°C or Cold 12°C on GI permeability and subjective GI symptomology was determined. GI permeability increased under both continuous and intermittent exercise compared to rest. No differences between continuous and intermittent exercise patterns were observed when undertaken in the cold. However, a stepwise increase in permeability was noted in the heat: Rest < SS < HIIT. Minimal expression of GI symptoms was noted and these were unrelated to the objective GI permeability markers. When relative exercise intensity is controlled for at 70% of a velocity associated with V̇O 2 peak no difference in GI permeability occur between HIIT and steady state exercise when this is undertaken in the cold. This response is abolished when exercise is undertaken in under HOT conditions but does not attain significance. Study 3 chapter 6 using a double blind repeated measures design examined the effects of HIIT exercise and the co-administration of Non-Steroidal Anti Inflammatory Drugs (NSAIDs) upon GI permeability and symptomology. Twelve trained intermittent games players participated. It was observed that HIIT exercise consisting off, repeated sprint activity [4 sets x 6 x 35 m (< 6s)] does not increase GI permeability relative to rest. Further when NSAIDS (2 x 400 mg Ibuprofen) are added to this model no further changes in gut permeability and symptoms are observed above that off the relevant control. These data suggest that following the present dosing regimen in trained male games players GI permeability and symptoms are unaffected by a single bout of HIIT exercise. Taken together the HIIT exercise model undertaken here and the co administration of Ibuprofen do not increase GI permeability seen with longer duration exercise. Finally, study 4 chapter 7 addressed whether exercise modality running vs cycling may be important in the development of GI disturbances give the epidemiological data that reports higher GI symptomology during and after running. Six male triathletes undertook three separate trials; a steady state 1000 kilojoule (KJ) cycling work test at 70% V̇O2 peak, an equivalent treadmill running protocol matched on total energy expenditure and equivalent period of non-exercise. Under these conditions GI permeability, as expressed by L:R ratio and GI symptoms were examined. Data indicate relative to rest an increase in GI permeability but indicate no modality specific differences in GI permeability and symptom expression between running and cycling. Running relative to cycling is associated with higher albeit still relatively limited subjective GI symptoms contrasting the equivalence seen in GI permeability L:R ratios. This disassociation in subjective symptoms and objective GI permeability in triathletes requires further consideration as regards mechanism of action and causality between these markers. This thesis has considered the effect of exercise intensity, modality and exercise patterning and their interactions with environmental stress upon objective and subjective markers of GI Function. Data suggest that exercise induced increases in GI permeability relative to rest occur when the exercise intensity and duration exceed a critical threshold of ~70 % peak aerobic capacity for at least 50 minutes. Manipulation of exercise patterning i.e. HIIT vs continuous undertaken at the same relative intensity shows no difference in GI permeability when under taken in the cold relative to the heat. Undertaking exercise in a Hot (32°C) environment accentuates permeability. Subjective GI symptomology does not mirror changes in the objective GI permeability markers with all subjective data indicating registering limited symptomology. It was further observed that HIIT exercise consisting of supra-maximal, short duration repeated sprints (<6s) performed on a repeated basis does not alter GI permeability. When NSAIDS are co-ingested with this model no further changes in gut permeability and symptoms are observed. Finally, exercise modality does not impact alter GI permeability and the relationship to GI symptomology.

Skeletal muscle mass is vitally important for the maintenance of health and quality of life into old age, with a plethora of disorders and diseases linked to the loss of this tissue. As a consequence, molecular biologists have extensively investigated both atrophying and hypertrophying skeletal muscle, in order to understand the molecular pathways that are induced to evoke both loss and growth of skeletal muscle. Despite huge progressions in the field, a full understanding of the molecular mechanisms that orchestrate growth and loss in skeletal muscle, remain elusive. In this regard, epigenetics, referring to alterations in gene expression via structural modifications of DNA without fundamental alterations of the DNA code, have recently become a promising area of research, specifically for its role in modulating genetic expression. However, the field of skeletal muscle epigenetics is in its infancy, and as such, there is currently a distinct paucity of research investigating this biological phenomenon. Herein, a genomic approach was utilised to examine the role DNA methylation plays in modulating the response, at both a genetic and phenotypic level, of mammalian skeletal muscle. The methodological and analytical approaches utilised in this thesis identify a number of important, novel and impactful findings. Firstly, it is identified that DNA methylation displays a distinct inverse relationship with gene expression during both muscular atrophy and hypertrophy, these findings are furthered by work identifying that DNA methylation alterations may precede functional changes in gene expression during skeletal muscle hypertrophy. This thesis also elucidated that skeletal muscle possesses an epigenetic memory that creates an enhanced adaptive response to resistance load induced hypertrophy, when the same stimulus was previously encountered. Finally, in human subjects, a number of novel and previously unstudied gene transcripts were identified that display significantly positive correlations with changes in skeletal muscle mass, as evoked by resistance training. The data in this thesis demonstrates an important role for DNA methylation in regulating skeletal muscle mass during periods of both muscle atrophy and hypertrophy, respectively. The work presented here may allow for further work to be conducted, expanding our understanding of epigenetics in skeletal muscle and best facilitating the development of therapeutics that may alleviate the detrimental effects observed during periods of skeletal muscle atrophy.