Élite adult athletes are known to have physical and physiological characteristics specifically suited to their sport. However, it is not clear whether the observed adult differences arise because of training or whether the sport selects the individual with the appropriate characteristics.The purpose of this study was to compare and contrast the physical development of young athletes (8 - 19 yr) and in so doing provide an answer to this question. Development of anthropometric characteristics, sexual maturation, pulmonary function and aerobic power were assessed in a group of 232 boys and 222 girls. The athletes were a randomly selected group of young athletes who had demonstrated previous performance success or who were excepted to do so in the future. They came from 4 sports namely: soccer (all male); gymnastics (2:1 female to male ratio), swimming (1:1 sex ratio) and tennis (1:1 sex ratio). The subjects were assessed annually for three consecutive years. The adjusted mean (ANCOVA) height of male swimmers (161.6 ± 0.6 cm) was found to be significantly greater (P<0.01) than non-athletes (159.2 ± 0.4 cm), gymnasts (150.7 ± 0.8 cm) and soccer players (158.7 ± 0.6 cm) and adjusted body mass (51.3 ± 0.6 kg) significantly greater (P<0.01) than the other groups. These trends were also observed in females. When testicular volumes were compared, it was found that swimmers matured significantly earlier (P<0.05) than gymnasts, tennis players and a reference population of non athletes. Female gymnasts attained sexual maturation (indexed by menarche) on average (14.4 ± 0.2 yr) a year after the other sports and the general population. A positive correlation was found between menarcheal age in mothers and daughters (r=0.29 , P<0.05), suggesting a familial trait. The observed late sexual maturation of gymnast therefore suggests some form of sports specific selection. Swimmers had the highest initial lung volumes (P<0.001), a difference which did not change with time. However, as training began well before the subjects were tested it was not possible to determine whether these observed differences were present prior to training. When age, height and weight were controlled for VO₂ max in males significantly increased both pubertal development, although this pattern was not shown in females. Swimmers had the highest VO₂ max values at all ages.

A cross-sectional study was designed to determine the relationship between aerobic fitness and resting metabolic rate (RMR) in 69 males exhibiting a wide range of aerobic fitness levels (V̇O2max = 32.8-78.1 mL · kg-1 · min-1). The results of this study indicated that RMR was not significantly different between trained and untrained individuals when expressed in kJ · kg fat-free weight-1 · hr-1 or using an ANCOVA with fat-free weight as the covariate and RMR as the dependent variable (F ratio = 0.353, P < 0.70). In addition, this study also failed to support a previously suggested hypothesis that an elevated RMR may only be observed in those individuals exhibiting both high V̇O2max values and currently training a minimum of 12- 16 h/wk. Thus, the results of this study strongly suggest that RMR is independent of both a person's current aerobic level and training status.

In a series of studies, lifestyle activities, mental health and aerobic fitness were investigated in relation to mean RT and response time variability (trial-to-trial variability in RT performance) obtained from a battery of cognitive measures in 257 healthy adults aged 50 to 90 years (M = 63.60). Cognition was assessed across four domains; psychomotor performance, executive function, visual search and word recognition. Hierarchical multiple regression analyses and structural equation modelling (SEM) were used to explore associations between age and outcome measures in a mediated-moderator analysis. The dedifferentiation of cognition and the dissociation between the outcome measures of mean RT and response time variability was also explored. Additionally, the neural correlates of response time variability were investigated using functional magnetic resonance imaging (fMRI). The findings indicated that poor mental health was associated with greater within-person (WP) variability and slower mean RTs and that this effect was greater in older adults. Higher lifestyle activity scores and higher aerobic fitness (VO2max) attenuated negative age gradients in WP variability and mean RT. Analyses suggested that the above effects were mediated by executive function. There was no evidence of dedifferentiation across cognitive domains and there was selective dissociation between the measures of mean RT and WP variability. The fMRI results suggested that WP variability was associated with fluctuations in executive control and, relatedly, attentional lapses. Overall, the findings suggest that executive function mediates a substantial portion of age-related variance in cognition and that this association is influenced by moderators such as an active lifestyle, aerobic fitness and mental health. The findings underline the potential benefits and importance of interventions to help maintain and promote mental health, and active lifestyles, in old age.

The purpose of this study was to examine the effects of aerobic fitness level on concussion risk, severity and recovery in high school football players. Participants (N=158) completed aerobic fitness (i.e., estimated VO2 max) and baseline neurocognitive tests (i.e., ImPACT). Concussed athletes completed ImPACT every 24-72 hours until they were asymptomatic or returned to baseline levels. A post-season questionnaire assessed unreported concussions and symptoms. Twenty players incurred concussions. Previously concussed athletes were 3.71 times more likely to be concussed than those with no concussion history. Severely concussed participants reported lingering symptoms. Previously concussed athletes high in aerobic fitness reported fewer symptoms than those low in aerobic fitness. Non-significant trends suggested that aerobic fitness might be related to faster recovery times and fewer symptoms. Twenty-eight percent (n= 38) of non-concussed participants reported a potential concussion and symptoms that were not recorded by medical staff during the season.

The present study evaluated direct and indirect associations between aerobic fitness, executive control, and emotion regulation among a sample of children aged 8-12 years. To evaluate these associations, the study employed a cross-sectional design and full-information maximum likelihood (FIML) structural equation modeling. Although the hypothesized factor analytic model failed to converge, an alternative exploratory model allowed for the evaluation of associations between primary study variables. Results supported a moderate direct association between childhood aerobic fitness and executive control, a strong direct negative association between executive control and emotion regulation, and a moderate indirect association between aerobic fitness and emotion regulation through executive control. These findings provide preliminary evidence that executive control functions as a mediator between aerobic fitness and emotion regulation and may help explain the means by which aerobic exercise exerts its influence on emotional wellbeing among preadolescent children.

The investigations described in this thesis were conducted in order to increase the understanding of the relationships between physical activity, aerobic fitness, body composition, asthma, and asthma severity in children and adolescents. This was largely achieved by examining the aforementioned factors in a sizeable population of Melbourne school children and adolescents. However, during the course of the school-based testing, it became apparent that the severe asthmatic category was under-represented, typical of the current literature. Thus, effort was also directed at addressing this knowledge gap by examining a severely asthmatic cohort in a laboratory-based setting. The outcomes generated by these investigations can be summarised as follows: 1) In ‘school-tested’ youth aged 10 to 14 years, prevalence rates of overweight and obesity were 19.1% and 4.0%, respectively. Approximately 16% of participants also suffered from asthma. These rates appear to be representative of similarly aged children and adolescents within Australia. The latter observation also adds weight to the view that asthma prevalence has attenuated in recent years. In addition, overweight and obesity were more prevalent in asthmatics than non-asthmatics, supporting the proposed notion of an asthma-obesity association. 2) Asthmatic and non-asthmatic young people had comparable aerobic fitness and daily physical activity levels and the severity of disease did not influence aerobic fitness nor involvement in physical activity. Males possessed greater aerobic fitness and physical activity levels and had a lower percentage body fat compared to age-matched females, independent of asthma status (i.e. asthmatic or non-asthmatic). 3) There was a significant inverse relationship between aerobic fitness and markers of increased body fat among non-asthmatic children and adolescents, even after corrections to aerobic fitness were made for fat free mass. Differences in daily physical activity could only partially explain this association. In fact, the current findings suggest that decreased levels of daily physical activity are not the cause of the increased overweight/obesity prevalence among this sample, and that physical activity lacks a strong link to paediatric overweight/obesity in this population. These findings were also present in asthmatic youth. 4) Severely asthmatic youth, premedicated with bronchodilator, had aerobic fitness levels comparable to their non-asthmatic and less severe asthmatic peers. This finding indicates that severely asthmatic youngsters should be able to train at work intensities sufficient to bring about improvements in cardio-respiratory fitness without any added functional limitation due to their condition. In addition, a state of well-controlled asthma (as were the severe asthmatics in this study) afforded the participants the ability to engage in similar levels of physical activity as their non-asthmatic or less severe asthmatic peers. In agreement with data from the ‘school-tested’ asthmatics, a significantly greater proportion of severely asthmatic participants were overweight or obese in comparison to their non-asthmatic peers. These findings (i) highlight the association between aerobic fitness and overweight/obesity; (ii) suggested that decreased levels of daily physical activity were not associated with the increased overweight/obesity prevalence in a youth sample within Australia; (iii) emphasize that well-controlled asthmatic young people can undertake levels of physical activity and achieve cardio-respiratory fitness similar to that of their non-asthmatic peers, independent of asthma severity, and; (iv) indicated that asthma is either a risk factor for overweight and obesity or that overweight and obesity may precede asthma.

Regular aerobic exercise may reduce cardiovascular disease (CVD) risk in part by lowering the concentration of inflammatory markers such as C-reactive protein (CRP). While studies in diseased populations have shown significant decreases in CRP concentrations with regular aerobic training, little has been conclusively determined regarding the effects of aerobic training on CRP concentrations in apparently healthy, untrained populations who may not be adequately screened for CVD risk by traditional methods. PURPOSE: To examine the effects of a 17-wk half marathon training program (TP) on CRP concentrations, aerobic fitness, and body composition in apparently healthy, untrained men. METHODS: Twenty men (29.3 ± 1.0 yr, 37.0 ± 1.6 mL•kg-1•min-1 VO2max, 29.1 ± 1.8% body fat) registered as training subjects (TRN) in a 17-wk half marathon TP. An additional 22 men (27.8 ± 1.4 yr, 38.8 ± 1.0 mL•kg-1•min-1 VO2max, 26.8 ± 1.4% BF) served as controls (CON). Fasting blood samples were taken at four time points over the TP and were analyzed for CRP and interleukin-6 (IL-6) concentrations. Aerobic capacity (VO2max) and body fat (BF%) were measured before and after the TP. RESULTS: No significant changes in CRP (P=0.69) or IL-6 concentrations (P=0.73) were seen in TRN as a result of the TP despite significant improvements in VO2max (42.2 ± 1.9 ml•kg-1•min-1, P<0.0001), resting heart rate (P =0.004), BF% (P =0.03) and BMI (P =0.05). No significant changes in CRP, aerobic fitness, BMI or BF% were detected in CON over time. CONCLUSION: Moderate, long-term aerobic training does not appear to affect CRP concentrations in apparently healthy, untrained men despite significant improvements in BW, BF%, BMI, and VO2max.

This dissertation examines the impact of exercise rehabilitation and the components of exercise prescriptions on optimizing health outcomes for people with diabetes (DM). Exercise is an accepted part of the diabetes management regime to help prevent or slow the progression of the disease. A combined aerobic and resistance training protocol is the recommended exercise regime for people with DM, but the question remains as to what the optimal dose may be for glycemic control and reduction of cardiovascular risk. This thesis aims to address three objectives surrounding optimal exercise prescriptions for diabetes: 1) To investigate aerobic exercise prescription efficacy in people with DM, coronary artery disease (CAD) and both CAD and DM to determine if there are population-specific VO2peak responses to exercise prescription; 2) To determine the optimal volume and intensity of resistance training exercise, in combination with aerobic training, that may improve glucose control, cardiovascular risk factors and body composition in people with type 2 DM (T2DM); and 3) To study the relationship between exercise performance, physiological changes and depressive mood in people with T2DM participating in a supervised, exercise program. Encouraging participation in an appropriately prescribed aerobic and resistance training program may help to improve adherence to exercise and elicit optimal health outcomes in people with T2DM. Tailoring the exercise prescription to suit the patient’s lifestyle, history and capacity is the utmost challenge for health care providers who hope to provide a complementary, non-pharmacologic therapeutic option for their patients.

The present study evaluated the associations between direct measures of aerobic fitness and executive functioning in pre-adolescent children aged 8 to 12 years. To evaluate these associations, the study employed a cross-sectional design and a series of three step hierarchical regressions were conducted. Results suggest that after controlling for age, sex, and BMI percentile, heart rate measures of aerobic fitness did not independently predict executive function. These findings provide preliminary evidence that contradicts a growing body of research within the adult literature demonstrating an association between aerobic fitness and executive function.

Previous reports have demonstrated that children’s physical activity is typically intermittent in nature. Accelerometers are reliable and valid tools for quantifying the pattern of activity in children. However, in order to interpret accelerometer output it is necessary to apply appropriate accelerometer thresholds for classifying physical activity intensity. Currently multiple accelerometer thresholds are available in the literature and it is unclear which are the most appropriate or whether thresholds should be sample specific. Additionally, there is little information regarding how the pattern of activity in children varies across groups and how activity patterns relate to health. The overall aim of the thesis was to describe the pattern of habitual physical activity, using objectively-measured physical activity data, in relation to health outcomes in pre-adolescent boys. The first objective was to characterize the pattern of boys’ habitual physical activity, using objectively-measured physical activity data. The second objective was to investigate the relationship between habitual physical activity and specific aspects of the activity pattern and health outcomes in boys. The final objective was to investigate the effects of continuously- versus intermittently- accumulated physical activity on acute health outcomes in boys, using an intermittent activity protocol based on the measured pattern of habitual activity in boys. The first four studies used a sample of 54 boys, aged 8 to 10 years. The final study used a different sample of 10 boys, aged 9 to 11 years. Both samples were from the county of Devon, UK. The first study of this thesis established sample-specific accelerometer-intensity thresholds through calibration research with ActiGraph accelerometers (counts•2s-1) in boys. The second study in the thesis demonstrated that relationships between time accumulated at different activity intensities and health (fatness, peak oxygen consumption and resting blood pressure) in boys were similar irrespective of whether sample-specific or published thresholds were employed as long as the threshold was at least equivalent to a brisk walk (i.e. >4 METs). However, the prevalence of children reported as meeting activity guidelines did differ according to thresholds employed. Study three showed that, despite little difference between overweight and normal weight boys in overall activity, time spent sedentary and minutes of light, moderate and vigorous intensity activity accumulated, aspects of the activity pattern (frequency, intensity and duration of ≥4 s (short) and ≥5-min (long) bouts of ≥light, ≥moderate, ≥vigorous and ≥hard intensity activity) differed by weight status. Overweight boys accumulated fewer and shorter bouts of activity, particularly sustained bouts of activity which were of moderate intensity or greater. Study four examined the relationship between activity pattern and health in boys further, focusing on body fatness, aerobic fitness, blood pressure and microvascular function. Results demonstrated that summary measures of activity were negatively related to body fatness, and positively related with both aerobic fitness (i.e., total, moderate, vigorous and hard activity) and endothelial function (i.e., total and light activity). Time spent sedentary was negatively related to endothelial function. The frequency and duration of activity bouts of ≥moderate intensity and the intensity of all activity bouts (i.e., ≥light intensity) were most important for body fatness and aerobic fitness. The frequency of all bouts (short and long) of at least light intensity was most important for endothelial health. Finally, study five moved away from chronic measures of health and examined the acute physiological effects of the recommended daily amount of physical activity (60 minutes of physical activity of ≥moderate intensity) on postprandial lipaemia and microvascular function in boys the following day. Furthermore, the study aimed to assess whether the effects differed depending on whether the activity was accumulated continuously or in a manner more similar to the children’s typical activity patterns identified in studies 3 and 4. In contrast to findings from adolescents and adults, 60 minutes of >moderate intensity activity did not impact on postprandial lipaemia or microvascular function the following day in healthy, active boys, regardless of how it was accumulated. The results of the present thesis indicate that aspects of the activity pattern are significantly related to health in boys and differ according to type of day and weight status. Furthermore, the benefits of sporadically-accumulated activity are equally as strong as continuously-accumulated activity to body fatness, aerobic fitness and endothelial health in boys. Since children typically accumulate short, intermittent bouts of activity, the promotion of sporadic activity (i.e., in intervention research and current physical activity guidelines for children and youth) might increase enjoyment and adherence. The benefits of acute intermittent exercise (which simulates free-living activity) on postprandial lipaemia and microvascular function in inactive children with risk factors for cardiovascular disease should be investigated. Longitudinal investigations into the activity pattern of a much larger and more age-diverse sample of boys and girls are needed to determine whether any changes in aspects of the activity pattern might alter these and other health outcomes (i.e., cardiovascular risk factors).