3. Body composition and cardiorespiratory fitness assessment: This study also aims to characterise the patterns of change in body composition, physical activity and cardiorespiratory fitness in breast cancer patients. The study will examine whether these modifiable factors might influence a patient's susceptibility to cardiac changes during treatment and, in turn, how these factors are affected by treatment. Of particular interest, it has been suggested that cardiorespiratory fitness (measured by the rate of oxygen uptake) is impaired in breast cancer patients compared to healthy controls, even seven years following the completion of treatment. Oxygen-uptake analysis will be performed in this study to explore possible compensatory mechanisms for abnormal pathology- or treatment-induced cardiac function in breast cancer patients. Fitness, physical activity and body composition will be assessed quantitatively using a range of objective techniques, including cardiopulmonary exercise testing on a cycle ergometer (fitness) with breath-by-breath gas analysis (cardiorespiratory function), accelerometery (activity levels) and DEXA radiography scans (body composition).