Background. Exercise duration of constant-load endurance tests has been recently demonstrated to be more sensitive in detecting the changes after bronchodilator administration than either walking distance or peak oxygen uptake in patients with COPD. In the present study, we questioned whether exercise duration of progressive load is better correlated with forced expiratory volume in 1 sec and inspiratory capacity than other indices of submaximal exercise test during stable period in patients with COPD. 

Methods. Thirty-three stable COPD patients, and 26 age- and BMI-matched control subjects were recruited. Resting pulmonary function tests and incremental cycle exercise tests were performed. All indices of exercise and pulmonary function tests including exercise duration, peak oxygen uptake (VO(2)peak), and forced expiratory volume in 1 see (FEV1) were recorded. 

Results. Exercise capacity was lower in COPD than age- and BMI-matched controls as shown by exercise duration and ergometric work (535 +/- 159 vs. 705 +/- 115 sec, p < 0.001 and 89.2 +/- 26.6 vs. 117.8 +/- 19.5 W, p < 0.001). Statistical analysis revealed that exercise duration slightly better correlates with FEV1 and inspiration capacity (IC) (R = 0.600, p < 0.001; R = 0.615, p < 0.001) than peak oxygen uptake (R = 0.284, p > 0.05; R = 0.127, p > 0.05) in stable period COPD patients. 

Conclusions. There is an impairment of aerobic capacity in stable period COPD patients compared to healthy controls. Exercise in COPD patients is ventilation-limited and exercise duration with respect to peak VO2 is better correlated with FEV1 and IC in stable COPD patients undergoing progressive-load cycling exercise.