This is a multicenter, randomized, double-blind, double-dummy, crossover study with two 2-week treatment periods separated by a 2-week wash-out period. Subjects will participate in up to eight study visits and have a follow up phone call approximately a week after the last clinic visit. Visits 1, 2, 3, 5 and 6 are evening visits that will be conducted between 5PM and 11PM. Visit 4 and Visit 7 are also evening visits that will begin between 5PM and 11PM and continue over a period of approximately 24 hours. Subjects will be required to attend three clinic visits during this 24-hour period. An exercise challenge (using a treadmill) will be conducted at Visit 2, Visit 3 and Visit 6 (after 23 hours of the first treatment dose in each Treatment Period); and at 12 and 23 hours post evening dose at Visits 4 and 7. Spirometry will be conducted at specified visits and prior to and after each exercise challenge.