Abstract:The psychological construct of affect is proposed to significantly contribute to pacing decisions during exercise. Borg's Ratings of Perceived Exertion (RPE) scale, another important regulator of work-rate, is criticised as an inadequate measure of the multiple perceptual responses experienced. This study aimed to examine power output distribution and associated changes in affect, self-efficacy, perceptual cues, heart rate and respiratory gases during both 16.1 km and 40 km self-paced cycling time trials (TT). Secondly, the differentiation between physical perceptions of exertion and sense of effort in self-paced exercise was investigated.Method: Fifteen trained male cyclists completed 16.1 km and 40 km TT using a CompuTrainer cycle ergometer. Time, power output distribution, affect, self-efficacy, physical RPE (P-RPE), 2 task effort and awareness (TEA), heart rate and respiratory gases were measured throughout each TT. Linear mixed models explored associations of these variables with power output distribution, and the relationship between P-RPE and TEA. Results: Similar pacing strategies were adopted in the 16.1 km and 40 km TT (p = 0.31) and main effects were found for affect