Reports of lumbar spine (IS) skeletal deficits in female athletes with menstrual disorders are common, although it is not clear whether the deficits are confined to this group. The main factor presumed to be responsible is oestrogen deficiency characterised by amenorrhoea, however emerging evidence indicates that energy deficiency can also disturb bone turnover. This thesis aimed to determine whether male distance runners are at a comparable risk for bone loss and whether there was a relationship between reported energy balance and BMD. Methods: 109 distance runners (18-50 years) participated (65 females, 44 males). A questionnaire assessed menstrual status, performance level and training characteristics. 7-day dietary and exercise records were used to quantify energy balance. LS, dual femur (DF) and total body (TB) BMD were measured using dual-energy X-ray absorptiometry. Bone size was accounted for: bone mineral apparent density (BMAD) = BMD / √Bone area. Results: Male and female IS T-scores were similar (-0.8, -0.8). 41.6% of female and 36.4% of male runners were osteopenic (LS). Age, BMI and body fat- adjusted LS T-scores were lower in male than female runners (p<0.05). Adjusted LS T-scores were lower in male compared to eumenorrhoeic runners (p<0.01). Female runners who used the oral contraceptive pill had similar BMD to amen/oligo-menorrhoeic runners, which were significantly lower than eumenorrhoeic runners (p<0.01). These runners were also more energy deficient (p<0.01). Elite runners had greater energy deficits, lower IS T-scores, BMAD and a smaller bone area than club runners (p<0.001). DF and TB T-scores were normal, did not correlate with weekly mileage and after adjustment for calcium intake, did not correlate with energy balance. IS T-score negatively correlated with stress fracture incidence (p<O.OOOI).Most runners were energy deficient and the severity of energy deficiency correlated with lower BMI and body fat. Energy balance was the strongest predictor of LS BMD and T-scores, Conclusions: Low LS BMD in distance runners is not gender-specific; the oral contraceptive pill may be insufficient to protect against bone loss in female runners and elite runners may be more at risk of bone fragility. Energy deficit was the underlying determinant of low BMD in male and female runners, emphasising the importance of energy balance for bone health.

Aims: Associations between negative self beliefs, motivation to exercise, mood and eating disorder (ED) symptoms in young women are poorly understood. Theoretically, young women may exercise to overcome negative self beliefs, which may help to maintain/encourage both low mood and ED symptoms. This study aims to enhance our understanding of these interrelationships and their role in the development and maintenance of some psychological disorders experienced by women. Results: No significant relationship was found between exercise with mood and ED symptoms. Negative self beliefs were found to be correlated with mood and ED symptoms. A high level of negative self belief (insufficient self-control/self-discipline) was correlated with low levels of exercise. Identified regulation was found to be a significant mediator between negative self belief (insufficient self-control/self-discipline) and exercise. Conclusion: With the provision of certain limitations, these results suggest that young women with negative self beliefs may exercise as a compensation or avoidance strategy. Exercising for motivations that mainly reflect a self-determined 'introjected' level of motivation impacted on an individual's anxiety levels.

The primary objective of these series of experiments was to develop an optimal hyperhydration strategy for use during conditions of restricted water access or exercise-induced heat stress. This strategy was composed of two compounds, namely Cr and Gly which each targeted specific body water compartments in order to maximise the volume of retained water. Endurance-trained subjects were recruited to participate in the current series of three experiments, and following Cr/Gly supplementation, body water was estimated by multifrequency bioimpedance and the physiological responses to exercise in the heat (30°C, 70% relative humidity) recorded and compared to pre-supplementation values. The aim of the first study presented in this thesis (Chapter 3(a)) was to examine the effects of combined Cr and Gly supplementation on fluid retention and subsequently the effects on cardiovascular, thermoregulatory and metabolic responses and performance during exercise in the heat. The aim of Chapter 3 (b) was to examine the effects of a novel method of Cr and Gly delivery and ingestion on fluid retention and distribution. Chapter 4 (a) aimed to assess the effects of Cr and Gly supplementation ingested according to the loading protocol described in the previous chapter (6 days of Cr and Gly ingestion, with the final supplement consumed 3 hours prior to measurement) on cardiovascular, thermoregulatory and metabolic responses and performance during exercise in the heat. The aim of the study in Chapter 4 (b) was to examine the effects of extending the period of time between ingestion of the final Cr/Gly supplement on the retention and distribution of fluid. The experiment in chapter 5 compared the effects of the novel Cr and Gly loading protocol established in Chapter 4 (b) on cardiovascular, thermoregulatory and metabolic responses and performance during exercise in the heat. The aim of Chapter 6 was to compare Tc measurements obtained using an ingestible telemetry pill and a tympanic membrane thermometer with those from a rectal thermistor during rest and high intensity exercise conducted in a hot and humid environment (30°C and 70% relative humidity) intended to raise Tc above 39°C.

Five experiments were conducted to examine the role of ball trajectory information in the planning, execution, and evaluation of a complex motor skill as a function of skill. This sensory information source could either be predicted to become either more (Koch et al., 2004) or less (Schmidt, 1975) important as skill is acquired. In Experiments 1,2, and 3 the importance of ball trajectory information in the execution of a soccer kick to a target as a function of skill was examined using visual occlusion (Exp 1 and 2) and perturbation (Exp 3) techniques. Skilled performers were able to maintain accuracy when vision of ball trajectory was occluded, although they were shown to use this information when it was available but perturbed. The accuracy of less-skilled performers decreased when vision of ball trajectory was occluded. Across skill groups, variability in knee-ankle coordination also decreased under these conditions. Although these finding was taken as evidence that across skill levels action effects information is used to execute the action when it is available, only at the lower levels of skill did this information aid outcome attainment. In Experiments 4 and 5 the importance of ball trajectory information in the planning of a soccer kick to a target as a function of skill was examined. Skilled and novice soccer players were instructed to plan the action in terms of the ball's trajectory or in terms of the body movements. There was little evidence that actions are more effectively planned by anticipation of their effects or that the ability to do so is skill-dependent (Koch et al., 2004). However, there was some evidence that a body-related focus was detrimental to performance in comparison to control conditions when feedback was removed (McNevin et al., 2003). Although ball trajectory information does not seem to be critical for task success, there was evidence that it is used to plan and perform actions across skill levels. Skilled performers were shown to be less reliant on this information compared to less skilled.

No description available.

The intuitive link between a runner’s gait and their metabolic cost of running, or running economy (RE), has led to many trying to compare the running mechanics of economical runners to those of less economical runners. However using this approach has created controversy about whether running mechanics meaningfully contribute to RE. Additionally only a limited number of studies use a broad, explorative, inter-disciplinary approach, encompassing physiological parameters, flexibility, kinematics, kinetics and muscular activity. The purpose of this thesis was to primarily assess ‘self-optimisation’ through considering acute and short-term adaptations to running mechanics and RE. To assess the biomechanical and physiological mechanisms behind changes to RE three studies were conducted, in addition to a fourth study which investigated biomechanical familiarisation. Study one investigated whether there were any biomechanical or physiological changes in beginner runners after 10 weeks of running and whether any of these changes contributed to a change in RE. There was an 8.4% improvement in RE (224  24 vs. 205  27 mL.kg-1.min-1) and an increase in treadmill time-to-exhaustion (16.4  3.2 vs. 17.3  2.7 min), but no change in ̇ 2max, minute ventilation or heart rate. Several kinematic, kinetic and flexibility measures were found to change over time, but joint moments and stiffness remained similar, with knee extension at toe-off, rearfoot velocity at touch down and timing of peak dorsiflexion explaining 94.3% of the variance in change in RE. Results from study one suggested that changes in muscular activity might have contributed to kinematic differences, and subsequently an economical gait. Specifically, as joint moments were unchanged after 10 weeks it is possible that muscular coactivation may have changed since varying levels of agonist-antagonist activation can produce the same joint moment. Consequently study two examined the relationship between muscular coactivation and the metabolic cost of running, as thus far there was conflicting evidence. Results showed that in trained, recreational runners greater thigh coactivation was associated with a greater metabolic cost of running. Furthermore, the speed of running was found to affect the level of coactivation at the shank and of the flexor-flexor muscle pair, with less coactivation reported at faster submaximal speeds. The final part of the thesis focused on a manipulation investigation into barefoot (BFT), minimalist shod (MS) and shod (SH) running. Applying the novel findings from studies one and two to this topical area would hopefully provide new insight into the 3 BFT running debate. Prior to applying this knowledge of kinematic and muscular activity changes in relation to RE whilst running BFT, an investigation into the time required to become familiar with barefoot treadmill running was needed. Results revealed that barefoot familiarisation was characterised by less plantarflexion and greater knee flexion at touch down, whilst stride length appeared to be adopted instantaneously. Reliability (intra-class correlations) and accuracy (standard error of mean) of the kinematic data appeared strongest once individuals had been running for 20 mins. Furthermore there were no significant differences in the kinematics after 20 mins of running. The final study considered how changing the levels of proprioception and cushioning (BFT, MS and SH) influenced RE and the potential running mechanics that contributed to any changes in RE. The ramifications of such changes on injury risk were also considered by investigating impact accelerations, effective mass and pronation. Additionally, the effect of naturally changing stride length from a shorter BFT stride to a longer SH stride on RE were examined. Heightened proprioception and no external cushioning (BFT running) appeared to improve RE by at least 5% regardless of stride length, when compared to SH running with a SH stride length. However less proprioception and no external cushioning (MS running) only improves RE, compared to SH running with a SH stride length, when runners run with their SH stride length, rather than their shorter BFT stride length (~2.5% shorter). Improvements in RE are attributed to a lower vertical oscillation and effective mass, greater dependency on efficient, Type I muscles i.e. tibialis anterior, and less plantarflexion at toe-off. However higher impact accelerations, earlier heel off and low pronation angles, suggest there may be an increase in injury risk. Therefore the findings from this thesis have demonstrated that runners naturally selfoptimise the way they run. This is seen both as an acute (changes in footwear) and short-term (10 weeks) response to changing running gait. Study two demonstrated that economical runners appear to use different muscular strategies, with study one and four showing they also adopt specific movement patterns that may promote efficient storage and release of elastic energy. Additionally study three found that runners can become familiar with BFT treadmill running in 20 minutes. It is also important to note that economical biomechanical adjustments do not always favour a reduction in injury risk. But the thesis findings seem to suggest that perhaps performance denominates in terms of self-optimisation, rather than injury prevention.

The work in this thesis has investigated the potential for a unique HMW glucose polymer (Vitargo, Swecarb AB, Sweden; MW of 500-700 g.mol-1) derived from barley starch to augment short-term post exercise muscle glycogen resynthesis above that of an isoenergetic LMW glucose polymer (Maxijul, SHS International, UK; MW of 900 g.mol-1). The HMW glucose polymer has been previously investigated in comparison to a LMW glucose solution with studies reporting a 70% greater muscle glycogen content after 2 hr recovery from glycogen-depleting exercise (Piehl-Aulin et al., 2000) and an enhanced gastric emptying at rest (Leiper et al., 2000). More recently an improved work output (10%) in a maximal exercise test performed 2 hr after exhaustive exercise was demonstrated after ingestion of the HMW glucose polymer compared to an isoenergetic LMW glucose polymer (Stephens et al., 2008). Key observations in this study were a greater rate of rise in blood glucose and serum insulin concentration during recovery with ingestion of the HMW compared to the LMW glucose polymer. Thus it was suggested that the improvement in performance in the secondary exercise bout could potentially be attributed to greater muscle glycogen availability present at the onset of the test. This hypothesis was subsequently tested initially in this thesis with the quantification of muscle glycogen content after cycling to exhaustion and ingestion of the same HMW and LMW glucose polymers. However, despite undertaking an identical exercise protocol, in contrast with the study by Stephens et al (2008), no differences in the rate of rise in blood glucose or serum insulin were observed. Accordingly muscle glycogen resynthesis measured 2 hrs after exhaustive exercise was similar following ingestion of the HMW and LMW glucose polymers (118 vs. 123 mmol.kg-1). Thus exercise performance in a secondary bout was near identical between both polymers (173 vs. 175 kJ). It was concluded that the LMW and HMW glucose polymers elicited similar post exercise muscle glycogen resynthesis however, since the sampling interval in this study using muscle biopsies was large (2 hr), it may have negated to highlight any early differences in muscle glycogen content. Therefore further investigation was undertaken that focused on more subtle sequential fluctuations in muscle glycogen by using ultra-high field 13C MRS following feeding of the same HMW and LMW glucose polymers. Marginal increases in muscle glycogen during 1 hr of recovery from prolonged exercise were reported after ingestion of the HMW and LMW glucose polymers (6 and 4% respectively). Additionally, increases in muscle glycogen after ingestion of both glucose polymers above that of a zero-energy control were not seen after 1 hr of recovery when a greater magnitude of resynthesis would be expected with the former. It was thus postulated that irrespective of the improved sensitivity of ultra-high field 13C MRS, the technique may not be suited to post exercise muscle glycogen resynthesis determination due to the methodological issue of subject positioning inhibiting typical gastric emptying patterns. When considering the implications of these studies it appears that the HMW glucose polymer does not augment post exercise muscle glycogen resynthesis above that of an isoenergetic glucose polymer with a much lower molecular weight. Nonetheless given that the blood glucose and serum insulin profiles over a 2 hr recovery in the first study of this thesis and the study by Stephens et al (2008) were notably different with the same test solutions, it was considered that there may be a disparity with the HMW glucose polymers utilised. Importantly the production of the HMW glucose has altered such that the manufacturing process has deviated from granulation to agglomeration with the native starch evolving from potato to corn and more recently barley. It was suggested that the most recent HMW glucose polymer used presently had deviated away from its initial characteristics leading to the blood glucose and serum insulin responses observed in the first study of this thesis. Indeed by then comparing post exercise ingestion of a previous granulated version of the HMW glucose polymer with a more soluble agglomerated version in the same experimental protocol as the first study, an initial greater rise in serum insulin was observed in the first 55 min of post exercise recovery. Thus alterations in manufacturing from granulation to agglomeration do appear to have affected properties related to postprandial insulin secretion. However this effect on insulin was not seen overall over the 2 hr recovery period and no differences in blood glucose or exercise performance in a secondary bout were observed suggesting other factors such as the native starch may be influential. It can thus be concluded that the difference in postprandial glucose and insulin responses seen between previous work and the present investigation may be due to altered physical characteristics of the HMW glucose polymer. No differences in intrinsic viscosity, rheology or molecular weight were noted between the agglomerated and granulated versions of the HMW glucose polymer thus the alterations in the origin material may account for more influence on digestibility in vivo. Further investigation would be warranted into effects on post exercise muscle glycogen resynthesis and exercise performance provided that the HMW glucose polymer could be returned to its original formulation.

Psychological well-being occurs when there is an absence of mental disorders and presence of positive states. Given the increasing prevalence of mental disorders, which are thought to have their roots in childhood, improving psychological well-being in children is currently an important area of research. Physical activity has been proposed as a method by which negative states can be reduced and positive states increased, thereby increasing children’s overall psychological well-being and in turn helping to protect against a decline into clinical disorders. Research focusing on physical activity and psychological well-being has mainly used self- reported measurements to assess physical activity, a method which leads to considerable non-differential misclassification that in turn will attenuate associations between physical activity and psychological wellbeing. Few studies have employed more precise, objective measures such as accelerometry. Despite providing a more precise measure of physical activity, a number of limitations are present with the use of accelerometry, specifically concerning the data reduction processes. Various decisions made when handling accelerometer data can result in misclassification of time spent in different intensities of physical activity and can introduce selection bias. The present thesis aims to address how the decisions made during data reduction can affect estimates of physical activity prevalence and alter the observed relationships between physical activity and psychological well-being in children. The first study of this thesis assessed the misclassification of activity intensities occurring as a result of the use of various accelerometer cut-points and the resulting variation in relationships between physical activity and psychological well-being that occurs. Results showed that the use of different cut-points to determine physical activity intensity alters the magnitude of the relationship between physical activity and psychological well-being; relationships were attenuated, with some becoming non-significant. The second study addressed the issue of children’s compliance with wear time requirements over multiple time points; compliance with wear time decreased over time, whilst inclusion and exclusion rules based on minimum wear times introduced selection bias. The use of more lenient wear time criteria, to reduce selection bias, introduced misclassification of physical activity intensities. Further, longitudinal relationships between physical activity and psychological well-being differed depending upon the wear time criteria employed. The third study aimed to address whether compliance, and in turn selection bias would systematically differ between groups of a trial of a physical activity intervention, and whether this would alter the results of the intervention itself. Results showed that compliance varied across trial condition, that selection bias with groups was different for each condition and that non-compliance hindered the exploration of the mediating effect of physical activity on psychological well-being. Study four involved the validation and calibration of a new wrist worn, waterproof physical activity monitor more compatible with 24 hour wear, thus potentially overcoming the compliance problems noted in the earlier studies. Results showed good concurrent and criterion validity, with high classification accuracy for the cut-points created. The final study assessed the acceptability and compliance with 24 hour wear in children and allowed a detailed examination of the underestimation of time spent in PA intensities that occurs from capturing shorter and different periods of the day. Results showed large misclassification with 10 hour capture periods relative to complete observation, with time in activity intensities varying across different periods of the day. The results of this thesis demonstrate that substantial selection bias and misclassification of time in activity intensities can be introduced through the decisions made during the processing of raw accelerometry data. Furthermore, this error alters the relationships between physical activity and psychological well-being. The results indicate that the true relationship between physical activity and psychological well-being in children may still be unknown, with researchers reporting relationships and effects only relevant to the measurement methods and data reduction processes they have employed. A method of overcoming selection bias and reducing misclassification is through 24 hour wear, which through the design of new accelerometers is now possible. Future studies should use monitors compatible with and acceptable for complete observation. This would result in more precise estimates of time spent in physical activity intensities and less selection bias. Both of these improvements would greatly increase our understanding of the relationship between physical activity and psychological well-being in children.

The hyperbolic power-duration relationship for high-intensity exercise is defined by two parameters: an asymptote (critical power; CP) reflecting the highest sustainable rate of oxidative metabolism, and a curvature constant (W'), which indicates a fixed amount of work that can be completed above CP (W>CP). According to the CP model of bioenergetics, constant work rate exercise above CP depletes the capacity-limited W' with fatigue occurring when W' is completely expended. The complete depletion of W' has been reported to occur when VO2max is attained and a critical degree of muscle metabolic perturbation (decline of finite anaerobic substrates and accumulation of fatigue-related metabolites) is reached. However, while the CP model is effective at predicting metabolic perturbation and the tolerable duration of severe-intensity constant work rate (CWR) exercise, it is unclear if metabolic perturbation and exercise performance can be explained by the CP model when different methods of work rate imposition are applied. Therefore, the purpose of this thesis was to: 1) investigate the efficacy of the CP concept to predict performance in exercise tests using different work rate forcing functions; and 2) explore whether the physiological bases for W' are consistent across different methods of work rate imposition. In study 1, compared to severe-intensity CWR exercise, the tolerable duration of intermittent severe-intensity exercise with heavy- (S-H) moderate- (S-M) and light-intensity (S-L) ‘recovery’ intervals was increased by 47%, 100% and 219%, respectively. W>CP (W') was significantly greater by 46%, 98%, and 220% for S-H, S-M and S-L, respectively, when compared to S-CWR, and the slopes for the increases in VO2 and iEMG were progressively lowered as the recovery work rate was reduced. In study 2, both the VO2max and W>CP were similar across incremental cycling protocols that imposed a fixed ramp rate and cadence (4.33 ± 0.60 L•min-1; 14.8 ± 9.2 kJ), a fixed ramp rate with cadence self-selected by the subjects (4.31 ± 0.62 L•min-1; 15.0 ± 9.9 kJ) and a step incremental test where subjects were instructed to select power output according to prescribed increments in ratings of perceived exertion (4.36 ± 0.59 L•min-1; 13.0 ± 8.4 kJ). In study 3, the VO2max and W>CP were also not different across a 3 min all-out cycling test (4.10 ± 0.79 L•min-1; 16.5 ± 4.0 kJ), cycling at a constant work rate predicted to lead to exhaustion in 3 min until the limit of tolerance (4.20 ± 0.77 L•min-1; 16.6 ± 7.4 kJ) and a self-paced 3 min work-trial (4.14 ± 0.75 L•min-1; 15.3 ± 5.6 kJ). In study 4, after completing severe-intensity exercise (>CP) to exhaustion, muscle homeostasis ([PCr], pH, [ADP] and [Pi]) returned towards baseline and subjects were able to exercise for at least 10 min at a heavy-intensity work rate (<CP); however, when the work rate was lowered but remained in the severe-intensity domain (>CP), muscle metabolites ([PCr], pH, [ADP] and [Pi]) did not recover and exercise tolerance was severely limited (39 ± 31 s). Finally in study 5, during severe-intensity intermittent knee extension exercise, the tolerable duration of exercise was 304 ± 68 s when 18 s recovery was allowed and was increased by ~69% and ~179% when the intermittent recovery periods were extended to 30 s and 48 s, respectively. The increased exercise tolerance with longer recovery periods occurred in concert with increased W>CP (3.8 ± 1.0 kJ, 5.6 ± 1.8 kJ and 7.9 ± 3.1 kJ for the intermittent protocols with 18, 30 and 48 s of recovery, respectively) and a delayed attainment of critical intramuscular metabolite concentrations ([PCr], pH, [ADP] and [Pi]). Therefore, the results of this thesis demonstrate that fatigue during various high-intensity exercise protocols is influenced by the capacity to complete work above the CP (W') and that W' depletion is linked to the attainment of VO2max and the attainment of critical levels of intramuscular [PCr], pH, [ADP] and [Pi]. These findings suggest that the CP model can be adapted to predict the degree of metabolic perturbation and exercise performance across a range of exercise settings in humans.

For sprint events longer than 100 m, more than half the race is run on the bend, yet bend sprinting has received little attention in biomechanics literature. The aim of this thesis was to understand the effect of the bend on maximal effort sprint performance and technique, using bend radii and surfaces typical of outdoor competition. Three empirical studies were undertaken with experienced bend sprinters. Initial 3D kinematics investigations revealed an approximately 5% velocity decrease on the bend compared to the straight. However, step characteristic changes contributing to this reduction were different for the left and right steps. For the left step there were significant decreases in step frequency (p < 0.05), due to increased ground contact time, which agreed with previously proposed theoretical models. For the right step, however, a significantly reduced flight time resulted in a significant reduction in step length (p < 0.05). Maintaining step length and an ‘active touchdown’ were closely related to an athlete’s ability to better maintain straight line velocity on the bend. Generally, velocity decreased as bend radius decreased, with mean differences of up to 2.3% between lanes 8 and 2. However, changes to athletes’ technique due to different lanes were not conclusive. Ground reaction forces revealed between-limb differences during bend sprinting. Furthermore, frontal plane forces were up to 2.6 times larger on the bend than on the straight. Overall, asymmetries were identified between left and right steps for several performance, technique and force variables, suggesting that bend sprinting induces different functional roles between left and right legs, with the left step contributing more to turning to remain on the bend trajectory. The differences in kinematic and kinetic characteristics between the bend and straight, and between-limb asymmetries mean that athletes should apply the principle of specificity to bend sprinting training and conditioning, without sacrificing straight line technique.