Bronchodilators and Lung Mechanics During Exercise in COPD

Bronchodilators are medications that open the bronchi to help patients with COPD to breathe better. It is still not known exactly how this effect improves shortness of breath in people with COPD. The goal of this clinical trial is to determine whether bronchodilators lower resistance in the smallest airways in the lungs, and whether this will improve the feeling of breathlessness in these patients. The main questions the investigators attempt to answer are: * In patients with COPD, does treatment with a short-acting bronchodilator improve small airway resistance during exercise? * In patients with COPD, does acute treatment with short-acting bronchodilator improve breathlessness and exercise endurance? The investigators will compare short-acting bronchodilators to placebo (a substance that contains no drug) to see if the bronchodilator medications improve small airway resistance and breathlessness during exercise. Participants will: * Visit the research laboratory 3 visits to complete tests of lung function and exercise * Complete 2 identical visits (Visit 2 and 3), one in which the participant receives bronchodilator and one in which the participant receives placebo.