The "feel better" effect of exercise has been well established, but the optimal intensity needed to elicit a positive affective response is controversial. In addition, the mechanisms underlying such a response are unclear. To clarify these issues, female undergraduate students were monitored for electroencephalographic (EEG) and self-reported affective responses during the recovery period following rest, low, moderate, and high intensities of treadmill running, each lasting 30 min. Frontal EEG asymmetry and self-reported vigor scores following exercise at all three intensities were significantly elevated compared to those observed following rest. The results suggest that steady-state aerobic exercise bouts executed at varying intensities induce a similar affective response during the recovery period when assessed at both the behavioral and psychophysiological levels. (Contains 2 tables and 2 figures.)