Results: The tidal volume increased significantly from 271.7 54.7 mL to 398.3 88.7 mL at the PSþ4 level (p Z 0.01). Significant differences in exercise duration were observed at different PS levels. The exercise duration was significantly longer at the PSþ4 level than at the PS and PSþ2 levels (146.3 139.9 seconds vs. 108.5 85.9 seconds vs. 72.8 43.9 seconds, p Z 0.038) as their corresponding order. There were significant relationships between resting respiratory rate and exercise duration at the PS (r Z0.639, p Z 0.034) and PSþ2 levels (r Z0.668, p Z 0.025).