Physical activity, aerobic fitness, body composition and asthma severity in children and adolescents

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.