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Background: Because treadmill exercise testing is more representative of daily activity than cycle testing, we developed treadmill protocols to be used in various clinical settings as part of a two-year, multicenter, chronic obstructive pulmonary disease (COPD) trial evaluating the effect of tiotropium on exercise., Methods: We enrolled 519 COPD patients aged 64.6 ± 8.3 years with a postbronchodilator forced expiratory volume in one second (FEV(1)) of 1.25 ± 0.42 L, 44.3% ± 11.9% predicted. The patients performed symptom-limited treadmill tests where work rate (Ẇ) was increased linearly using speed and grade adjustments every minute. On two subsequent visits, they performed constant Ẇ tests to exhaustion at 90% of maximum Ẇ from the incremental test., Results: Mean incremental test duration was 522 ± 172 seconds (range 20-890), maximum work rate 66 ± 34 watts. For the first and second constant Ẇ tests, both at 61 ± 33 watts, mean endurance times were 317 ± 61 seconds and 341 ± 184 seconds, respectively. The mean of two tests had an intraclass correlation coefficient of 0.85 (P < 0.001). During the second constant Ẇ test, 88.2% of subjects stopped exercise because of breathing discomfort; 87.1% for Global Initiative for Chronic Obstructive Lung Disease (GOLD) Stage II, 88.5% for GOLD Stage III, and 90.2% for GOLD Stage IV., Conclusion: The symptom-limited incremental and constant work treadmill protocol was well tolerated and appeared to be representative of the physiologic limitations of COPD.