Respiratory frequency is strongly associated with perceived exertion during time trials of different duration.

In order to provide further insight into the link between respiratory frequency (f_R) and the rating of perceived exertion (RPE), the present study investigated the effect of exercise duration on perceptual and physiological responses during self-paced exercise. Nine well-trained competitive male cyclists (23 ± 3 years) performed a preliminary incremental ramp test and three randomised self-paced time trials (TTs) differing in exercise duration (10, 20 and 30 min). Both RPE and f_R increased almost linearly over time, with a less-pronounced rate of increase when absolute exercise duration increased. However, when values were expressed against relative exercise duration, no between-trial differences were found in either RPE or f_R. Conversely, between-trial differences were observed for minute ventilation (_E), O₂ and heart rate (HR), when values were expressed against relative exercise duration. Unlike the relationship between RPE and both _E and HR, the relationship between RPE and f_R was not affected by exercise duration. In conclusion, f_R, but not _E, HR or O₂, shows a strong relationship to RPE and a similar time course, irrespective of exercise duration. These findings indicate that f_R is the best correlate of RPE during self-paced exercise, at least among the parameters and for the range of durations herein investigated. [ABSTRACT FROM AUTHOR]