<qa>  What is the main purpose of this study?In people with mild COPD, the ability to exhale air from the lungs is partly limited because of narrowing and collapse of the airways. This results in the trapping of air within the lungs and over-distention of the lungs and chest - this is known as lung hyperinflation. We believe that breathing at high lung volumes hyperinflation is an important cause of breathing discomfort dyspnea in people with COPD. Bronchodilators help to relax muscles in the airways or breathing tubes. Bronchodilators are often prescribed if a cough occurs with airway narrowing; this medication can reduce coughing, wheezing and shortness of breath. Bronchodilators can be taken orally, through injection or through inhalation and begin to act almost immediately but with the effect only lasting 4-6 hours. The main purpose of this study is to examine the effects of inhaled bronchodilators on breathing discomfort and exercise endurance in patients with mild COPD. 