To examine whether the validity of perception-based intensity regulation would be affected by exercise duration, 20 subjects were recruited to complete a maximal exercise test (GXT) and four submaximal trials of varying duration and intensity using a cyle ergometer. During GXT, ratings of perceived exertion (RPE), oxygen uptake VO2, heart rate (HR), and power output (PO) equivalent to 50 and 75% VO2peak were determined. During each trial, subjects were to produce and maintain a workload using RPE estimated at 50 or 75% VO2peak for 20 or 40 min, and VO2, HR, and PO were measured throughout the exercise. No differences in average VO(2) were found between the estimation and production trial of either duration. However, average HR and PO were lower (P < 0.05) during the production trial of both durations. It appears that exercise duration has a minimal impact upon the accuracy of using RPE to regulate a target metabolic demand.