Using a mixed-method approach, the aim of this study was to explore affective responses to exercise at intensities below-lactate threshold (LT), at-LT, and above-LT to test the proposals of the dual-mode model. These intensities were also contrasted with a self-selected intensity. Further, the factors that influenced the generation of those affective responses were explored. Nineteen women completed 20 min of treadmill exercise at each intensity. Affective valence and activation were measured, pre-, during and postexercise. Afterward, participants were asked why they had felt the way they had during each intensity. Results supported hypotheses showing affect to be least positive during the above-LT condition and most positive during the self-selected and below-LT conditions. Individual differences were greatest in the below-LT and at-LT conditions. Qualitative results showed that factors relating to perceptions of ability, interpretation of exercise intensity, exercise outcomes, focus of concentration, and perceptions of control influenced the affective response and contributed to the individual differences shown in the quantitative data.