Decreased levels of physical activity is common amongst individuals with Chronic Obstructive Pulmonary Disease (COPD) and has been directly associated with reduced survival, decreased quality of life and increased health care utilisation. Physical activity is a complex, multifactorial behaviour, and the development of multi sensor physical activity monitors has enabled researchers and clinicians alike to quantify this behaviour with greater degree of accuracy. However, despite this improved measurement capacity the clinical characteristics related to physical activity in COPD remain unclear. Using a historical data-base, the aim of this thesis was to examine how standard clinical characteristics such as anthropometry, lung function, exercise capacity (assessed by the sixminute walk distance) and quadricep strength were related to physical activity in two groups of COPD patients, one group with more severe disease referred to outpatient lung transplant assessment (pre-LTx group) (n=90) and another with less severe disease referred to attend a tertiary outpatient pulmonary rehabilitation program (pre-PR group) (n=70). This retrospective cross-sectional study included COPD patients that attended The Prince Charles Hospital between 2008 and 2013 and had a valid measurement of physical activity level as recorded by the SenseWear Armband.