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The detrimental nature of movement variability has recently been reconsidered with suggestions that it has a functional role to play in performance. Movements in golf can be attributed to the organismic, task and environmental constraints from which they emerge with these swing movements affecting shot outcomes. A three-dimensional analysis of address position variability revealed that higher skilled golfers present reduced alignment variability in angular relationships between the shoulders and stance compared to less skilled counterparts. Whilst there were no group differences in impact variability, both points in the swing displayed reducing variability from proximal to distal aspects of the kinetic chain. With the popularity of strength and conditioning growing within the golfing world it has become important for coaches to be able to assess golfers’ physical constraints. Two-dimensional analysis, representative of that used in coaching environments, assessed the relationship between the overhead squat and deterioration of posture in the golf swing. Results showed small but significant relationships between this test and golf swing postural kinematics. An 8-week intervention to address overhead squat physical constraints resulted in no change in 3D swing kinematics. Strength and conditioning as a stand-alone intervention provides no benefits to postural kinematics suggesting the need for coaching.

This thesis examines the effects of psychosocial factors and physical activity on antibody response to vaccination in healthy young, older, and HIV+ populations. Chapter Two found that a brisk walk prior to vaccination did not improve antibody response to pneumococcal or influenza vaccinations in young (18-30yrs) or older (50-64yrs) adults. Chapter Three examined whether a lifestyle physical activity intervention affected antibody response to pneumococcal vaccination in sedentary middle-aged women. There was no effect on antibody response, body composition or fitness measures, although there was an improvement in quality of life for the intervention group. Finally, Chapter Four investigated the relationship between psychosocial and physical activity status and antibody response to vaccination in HIV+ patients. Antibody response to some strains of the pneumococcal vaccine were predicted by higher physical activity levels (pn1, pn6b, pn18c), greater social support (pn3) and lower life events stress (pn1). However, the majority of analyses found that antibody response to vaccination was not affected by these measures. In conclusion, neither acute nor chronic walking interventions improve antibody response to vaccination, and only limited relationships are seen between psychosocial factors, physical activity status and antibody response to a variety of vaccinations.

The mammalian target of rapamycin (mTOR) complex is a key regulator of protein synthesis, with resistance exercise and protein ingestion both shown to increase mTOR activity in human skeletal muscle. It has recently been proposed that mTOR activity is regulated via its intracellular localization and protein complex interaction. However, no research to date has examined this process in human skeletal muscle. Accordingly, the aims of this thesis were to (1) develop immunofluorescent-based methodologies to study mTOR in human skeletal muscle, and (2) apply this approach to the study of mTOR in acute and chronic resistance exercise scenarios. This thesis describes a novel approach to study mTOR regulation in human skeletal muscle in vivo. Taking advantage of this approach, novel data was presented on mTOR distribution, translocation and association with regulators in response to resistance exercise in human skeletal muscle in vivo. It is hoped that this approach will provide insight into the cellular regulation of skeletal muscle protein synthesis and by extension the control of skeletal muscle mass in humans during scenarios of health and chronic disease.

Taking part in regular physical activity leads to adaptive response that enables the body’s antioxidant defence to be better equipped to fight against oxidative stress. Exercise intensity seems to be one of key factors that determines the effectiveness of exercise. The work presented in this thesis used novel approaches, through the application of emerging technologies, to study physical activity and its effects. This thesis contributes to the existing literature by being the first to investigate the effect of exercise on a marker of oxidative stress in the brain, an organ that becomes impaired (including oxidative damage) with ageing and diseases associated with ageing. The finding from this thesis suggests that brain glutathione (GSH) of young sedentary men as measured by magnetic resonance spectroscopy (MRS) was altered in response to acute exercise, in an exercise intensity dependent manner. Observed changes in peripheral markers of oxidative stress were also exercise intensity dependent. The brain seems to be protected against hyperperfusion injury during high intensity phase of high intensity interval exercise. Objectively measured physical activity levels were not significantly increased by an unsupervised home-based exercise intervention in older adults, potentially due to a lack of progressive goals based on adherence to physical activity.

The thesis outlines a collaborative research project that was undertaken between the Malta Football Association (MFA), the Malta National Sports School (NSS) and Liverpool John Moores University (LJMU). Drawing on transition frameworks, models and contemporary literature (Schlossberg, 1981; Stambulova 2003; Wylleman & Lavalle, 2004; Morris, Tod & Oliver, 2015; Morris, Tod & Eubank, 2016; Richardson, Littlewood & Gilbourne, 2005; Richardson, Littlewood, Nesti & Benstead, 2012), the research adopted an action research methodology to examine the psycho-social and cultural challenges that young Maltese football players and parents experienced within migratory based transitions. The author adopted the role of practitioner-researcher to understand, plan and support a range of key stakeholders during the transition process. Specifically, Study One (Reconnaissance Phase) examined the challenges experienced by Maltese footballers that had migrated to European professional football. Individual semi-structured interviews were conducted with 12 male Maltese players who had experienced migration to a foreign club. Results evidenced that players experienced homesickness and lacked psycho-social knowledge and skills for an effective transition. Players also experienced culturally based challenges. The findings are framed around a unique and deeply embedded Maltese cultural identity. Study Two (Reconnaissance Phase) utilised a focus group methodology with parents of players from the Maltese Football Association (MFA) Academy, parents of young players that had previously experienced migration, head coaches from top Maltese nurseries, and coaches from the National Sports School (NSS) and MFA. Findings of Study One were disseminated to facilitate reflection, discussion and to identify issues that required consideration in order to better prepare young players for future migratory based transition. Study Three (Action Planning) used focus groups to disseminate the findings of Study One and Two with the Headmaster of the NSS, and parent representatives of the school. A number of change strategies were developed to improve the school’s programme of preparation for students who may migrate to foreign clubs. A separate action meeting was conducted with the Technical Director of the MFA to discuss and highlight change strategies to improve the MFA’s programme of preparation for young footballers seeking a career abroad in professional football. The Implementation and Monitoring phases focused on applying the action strategies agreed. These were; (i) to experience migration and independent living, (ii) psycho-social and cultural support and development of young players, and (iii) parental education. Regular evaluation of change strategy activities evidenced positive change and also continued to enhance the efficacy of the strategies being implemented. Young players who have migrated overseas over the past year and who had engaged in a programme of preparation prior to migration have coped well with the challenges they have so far faced.

Alzheimer’s disease (AD) is a devastating neurodegenerative disorder which is thought to affect 26.6 million individuals worldwide. There is growing concern over a worldwide dementia epidemic that is predicted to develop over the coming decades. The evidence thus far suggests that increased levels of oxidative stress and vascular risk factors are two major contributors, amongst others, to AD development. The thesis aimed to investigate markers of oxidative stress in AD plasma. Moreover, the oxidative status of specific proteins was investigated using both hypothesis driven and proteomic approaches. Results presented in this thesis suggest that global plasma protein oxidation levels are not different when AD and control subjects are compared, but that individual plasma proteins are specific targets for oxidative modification in AD. The thesis explores different methodologies to assess oxidative changes in AD. In addition it demonstrates that emerging novel and powerful mass spectrometry techniques can be employed successfully to identify several proteins modified by oxidation, providing an initial starting point for further investigation.

Climbing stairs is a lifestyle physical activity with effects on a range of CVD risk factors. This thesis explored the potential of stair climbing at home as a public health intervention in three empirical studies. A pilot study tested the feasibility of progressive increases in stair climbing and descent at home. Eight participants progressed from 10 floors.day-1 in week one to 19 floors.day-1 in week four. Percent body fat, SBP and leg power were improved at the end of the brief intervention. The second study randomly allocated 24 healthy weight (BMI = 22.1) and 26 overweight (BMI = 31.7) sedentary women to gym-based and home-based stair climbing for 5 days.week-1 over 8 weeks, with a healthy weight control group recruited for comparison. Intervention participants progressed from 2 continuous 32.8m ascents.day-1 in weeks 1-2 to 5 ascents.day-1 in weeks 7-8. Stair climbing improved body composition, cardio-respiratory fitness and serum lipid profiles. Increases in leg power were found in the stair climbing group. Overall, effects were similar for gym-based and home-based interventions. Given the effects of leg power, and the importance of leg power in the elderly, the third study investigated the potential psychological determinants of increased stair climbing at home for an older population. Participants (n = 281; age = 69.2 years) reported the number of floors that they were willing to climb continuously at home, as well as potential barriers and facilitators of the behaviour. Positive beliefs about the benefits of regular stair climbing and fear of falling, both on stairs and in general, were the major predictors of willingness to climb stairs at home. Discussion focuses on the potential of home-based stair climbing as a cost-effective intervention for preservation of function and CVD risk in public health.

Perception of effort, defined as “the conscious sensation of hard, heavy and strenuous exercise”, is known to regulate endurance performance and human behaviour. Perception of effort has recently been shown to be exacerbated by mental exertion and is also known to be a main feature of fatigue. However, to date, not only its neurophysiology but also how manipulations of perceived exertion might impact endurance performance remain poorly understood. The main aim of this thesis was to investigate how manipulations of perceived exertion might impact endurance performance. This thesis is divided in two parts: central and peripheral manipulations of perceived exertion. In each part, three experimental chapters aimed to get a better insight in the neurophysiology of perceived exertion and its impact on endurance performance. In the first part (central manipulations), we firstly investigated the impact of exacerbating perceived exertion via mental exertion involving the response inhibition process on self-paced running endurance performance. This study demonstrated that as with time to exhaustion tests, time trial performance is impaired following mental exertion leading to mental fatigue. Secondly, we investigated whether mental exertion leading to mental fatigue could alter the rate of central fatigue development during constant load whole-body exercise. This study demonstrated that the exacerbated perception of effort in presence of mental fatigue does not reflect an altered rate of central fatigue development, but is likely to be due to i) an impaired central motor command and/or ii) an alteration of the central processing of the corollary discharge. Thirdly, we investigated whether mental exertion could impact the repeatability of maximal voluntary contraction of the knee extensors. We found that contrary to submaximal exercise, force production capacity is not altered by mental exertion. Finally, these three studies demonstrated that i) mental exertion negatively impacts submaximal exercise but not maximal exercise and that ii) mental fatigue differs from central fatigue. In the second part (peripheral manipulation), we firstly developed and tested the reliability of a new endurance exercise model non-limited by the cardiorespiratory system (one leg dynamic exercise), which will be of benefits for future researches aiming to manipulate feedback from group III-IV muscle afferents. Secondly, we described neuromuscular alterations induced by this exercise and tested a new methodology to indirectly measure feedback from group III-IV muscle afferents. This study demonstrated that one leg dynamic exercise induced central and peripheral fatigue and also a decrease in spinal excitability associated with an increase in cortical excitability. Furthermore, this study also suggests that monitoring cardiovascular responses during muscle occlusion might be a suitable tool to indirectly measure feedback from group III-IV muscle afferents. Thirdly, we tested the corollary discharge and afferent feedback model of perceived exertion with electromyostimulation. This study demonstrated for the first time that for the same force output, perception of effort generation is independent of muscle afferents and reflects the magnitude of the central motor command (manipulated by electromyostimulation). All together, these findings provide further evidence in support of the corollary discharge model of perceived exertion, and provide a new exercise model to investigate and manipulate perception of effort. This thesis, when integrating both experimental parts, provides new insight on how perception of effort regulates endurance performance. Specifically, it demonstrates how muscle fatigue is a contributor of the continuous increase in perception of effort during endurance exercise, but also that other contributors play a role in this increase in perception of effort. Indeed, we demonstrated for the first time that i) perception of effort alterations in the presence of mental fatigue is independent of any alterations of the neuromuscular system, and ii) muscle afferents does not directly impact perception of effort, but may influence it indirectly via their role in motor control.

There is no information available in the scientific literature that documents a specific assessment protocol for analysing a soccer player’s maximal power capabilities. As soccer-associated muscular power has not previously been investigated, it is not known how important power is in elite soccer and, if it is, the physiological and genetic determinants of soccer-associated power remain unknown. Such information could be used to optimise soccer-specific talent identification and development strategies. With this in mind, the overriding aim of our thesis was to investigate the physiological and genetic factors underpinning powerful actions in elite youth soccer. When devising an assessment of soccer-associated muscular power, there needs be a detailed analysis of the specific actions performed during elite competitive match-play that can be described as powerful. The aims of our first experimental study (Chapter Three) were to compare the frequency and durations of powerful actions during competitive English Premier League [under 18 (U18) and under 21 (U21)] elite youth soccer matches using a novel soccer specific powerful action (SSPA) notational analysis coding system. We found that while elite soccer match-play requires players to perform powerful actions in multiple directions [68 horizontal accelerations (in the horizontal-forward or mediolateral directions), eight sprints, and six vertical jumps (three bilateral and three unilateral)], horizontal accelerations of short duration (< 1.5 s) from different starting speeds were the most dominant type of explosive action. This activity profile provides a strong rationale for devising a muscular power assessment protocol that evaluates the ability to produce maximal power in multiple directions, from a unilateral stance. Our data also suggests that such a protocol could provide a specific lower body power profile in elite soccer players (ESP). The aim of our second study (Chapter Four) was therefore, to determine whether countermovement jumps (CMJs) in different directions [CMJs: bilateral vertical (BV), unilateral vertical (UV), unilateral horizontal-forward (UH) and unilateral medial (UM)] assessed independent lower-limb power qualities, and if CMJ performance differed between ESP (representing an English Premier League Academy regularly at U18 and under U21 levels) and non-elite soccer players (NSP). We found that unilateral CMJs in different directions assessed independent peak vertical power (V-power) and resultant take-off velocity capabilities, and the UH CMJ required significantly greater bicep femoris electromyographic (EMG) activation in comparison all other CMJs. Moreover, in comparison to NSP, ESP achieved greater V-power during all CMJs (p≤0.032) except for BV (p=0.197), and also achieved greater UH CMJ projectile range (51.6 ± 15.4 vs. 40.4 ± 10.4 cm, p=0.009). Our results suggest that unilateral CMJs in different directions, but not the commonly used BV CMJ, are determinants of U18 and U21 elite soccer playing status and can be used by applied practitioners as independent assessments of soccer-associated muscular power. As the physiological determinants of performance are of use to the applied practitioner for informing talent identification criteria, and prescribing detailed training intervention strategies, the primary aims of the third and fourth studies were to investigate the neuromuscular (Chapter Five) and tendon (Chapter Six) determinants of unilateral CMJs oriented in different directions. Our data suggests that unilateral CMJ performance is associated with direction-specific neuromuscular and tendon properties in U18 and U21 ESP. While UV CMJ performance was related to the size (quadriceps femoris muscle volume and physiological cross sectional area), architecture (vastus lateralis pennation angle) and ability to activate (vastus lateralis EMG activation level) the knee extensor muscles, UH CMJ performance was related to the elongation and compliance properties of the patellar tendon, and was inversely correlated with vastus lateralis fascicle pennation angle. Our findings highlight the importance of targeting specific neuromuscular and tendon properties when assessing and developing muscular power performance in U18 and U21 ESP. Many physiological changes occur during puberty (Viru et al., 1999) and our findings in Chapters Four, Five and Six may only be applicable in U18 and U21 ESP. Therefore, in our fifth study (Chapter Seven) we aimed to investigate the importance of acceleration, sprint, horizontal-forward CMJ and vertical CMJ capabilities at different stages of maturation in elite youth soccer. Elite soccer players and CON were grouped using years from/to predicted peak height velocity (PHV, a measure of growth velocity and an indirect measure of pubertal phase) to determine maturation status (ESP: pre-PHV, n=100; mid-PHV, n=25; post-PHV, n=88; CON: pre-PHV, n=44; mid-PHV, n=15; post-PHV, n=54). By comparing performance of ESP and control participants (CON) matched for maturation status, we found that acceleration and sprint performance were associated with elite youth soccer at all stages of maturation, but maximal power (horizontal-forward and vertical jumping) capabilities may only be important for elite youth soccer at mid- and post-peak height velocity. Our data could imply that assessments of acceleration and sprint capabilities should be included in soccer talent identification protocols at all stages of maturation, but maximal power should only be included at mid- and post-PHV. The purpose of our sixth experimental study (Chapter 8) was to investigate if specific gene single nucleotide polymorphisms [SNPs: ACTN3 R577X (rs1815739), BDNF G > A (rs6265), COL5A1 C > T (rs12722), and COL2A1 C > T (rs2070739)] played a role in determining elite youth soccer player status, and speed and power capabilities, in ESP and CON at different stages of maturation. We found that ACTN3 R- and BDNF G-allele frequencies were more frequent in post-PHV compared to pre-PHV ESP. Moreover, while the COL2A1 CC genotype was associated with greater horizontal power and faster 20 m sprint performance, BDNF GG genotype appears to positively influence 20 m sprint performance during the pre-PHV period only. Overall, our findings illustrate that elite soccer may require different genetic profiles before and after maturation, and genetic screening could be included in talent identification criteria to help predict maximal power and sprint potential in ESP. In summary, we devised a muscular power assessment battery that measured independent power qualities and could discriminate between U18 and U21 ESP and NSP. Our subsequent analysis showed that the physiological factors underpinning unilateral CMJ performance were direction-specific, and UV and UH CMJ capabilities were underpinned by separate neuromuscular and tendon properties, and should be assessed and developed, independently in U18 and U21 ESP. We then recruited a larger cohort of ESP and CON, at different stages of maturation, and demonstrated that muscular power was important for elite soccer performance at mid and post-PHV, but not pre-PHV. Finally, we showed that genetic profiles of ESP differed between pre- and post-PHV, and that certain gene variants [COL2A1 C > T (rs2070739), BDNF G > A (rs6265)] were associated with specific power and speed capabilities in ESP. Overall, our studies provide novel information that could have significant implications on soccer-associated power related talent identification and training intervention strategies in elite youth soccer academies.