 Expiratory airflow limitation is the most obvious physiological change associated with chronic obstructive pulmonary disease COPD. A consequence of airflow limitation is gas trapping as expiration becomes flow limited. This may occur at rest with more severe airway obstruction and is most evident during exercise as lung emptying is reduced and increased ventilation does not allow full expiration. This increased gas trapping or hyperinflation is the cause of much of the increased work of breathing, dyspnea, and exercise intolerance in subjects with COPD ODonnell 1997; ODonnell, 1993. Spirometric measurement of airflow limitation, particularly as assessed by forced expiratory volume in one second FEV1, is commonly used for the diagnosis of and assessment of response to pharmacotherapeutic intervention in COPD. However, changes in FEV1 may not fully predict symptomatic responses and alternative measures of lung hyperinflation such as exercise tolerance and exertional dyspnea may be more sensitive to therapeutic intervention andor more clinically relevant than FEV1 ODonnell1999; Bauerle, 1998; ODonnell, 1998; Officer, 1998. GSK573719GW642444 Inhalation Powder, a combination of the long-acting muscarinic antagonist LAMA bronchodilator GSK573719 and the long-acting beta2-agonist LABA bronchodilator GW642444, is in development for the maintenance treatment of airflow obstruction associated with COPD. Development of this product is supported by studies showing improvement in lung function with similar safety when use of combinations of long-acting bronchodilators with different mechanisms of action are compared with single bronchodilator therapy van Noord 2005; van Noord van Noord 2006; Tashkin 2008. Previous studies have demonstrated that treatment with short- and long-acting bronchodilators including ipratropium, tiotropium, and salmeterol reduces resting lung hyperinflation as measured by functional residual capacity FRC, residual volume RV, and inspiratory capacity IC, with associated improvements in exercise endurance time and exertional dyspnoea in subjects with COPD Ayers, 2001; ODonnell 1998; ODonnell 2004; Pepin 2005; Pepin 2007; Ramirez-Venegas 1997. However, the effect of combined LAMALABA therapy on these measures is not well characterized. 