Objectives: To monitor the effects of exercise intensity on regular exercisers' emotions, stress and effort.Design: A two-period crossover design was used in each of two within-subjects field experiments.Methods: Participants were two different groups of regularly exercising male students. Each group exercised using their usual exercise mode in their usual exercise environment. Group 1 (n=38) ran 5.0 km at low and high intensities, Group 2 (n=36) ran 1.7 km at low and high intensities. The analysis of results also examined differences between fast and slow runners.Results: Doubly multivariate (DM) analysis was used in the statistical analysis which indicated that significant changes occurred in pleasant and unpleasant emotions pre- to post-running 5.0 km and 1.7 km. No significant results between high and low running intensities were obtained for the 5.0 km distance. For exercisers running 1.7 km, significant differences between high and low intensity running were found for bodily stress and effort. Several significant findings for pleasant emotions were also obtained between fast and slow runners pre- to post-exercise.Conclusions: The atheoretical nature of some previous studies was avoided by utilising reversal theory's broad range of pleasant and unpleasant emotions as the basis for measurement and analysis. The results show that, for regular exercisers, exercise can lead to improved positive affect and support findings obtained in other studies.