The overall purpose of this investigation was to explain the acute exercise-affect relationship by examining potential individual difference variables with strong conceptual frameworks.  The moderator variables were exercise training history, personality temperaments, and resting brain asymmetry.  Solomon's opponent-process thoery of acquired motivation was tested in regard to exercise training history.  Davidson's framework that posits resting frontal EEG asymmetry as a biological marker of approach- and withdrawal-related motivation was examined.  In addition, unique to the present investigation, Gray's theory of personality was examined in relation to extraversion and neuroticism as potential moderators of the acute-exercise affect relationship.  A sample of 53 participants who were chosen based on their respective aerobic exercise training histories.  All participants completed the following three 30-min conditions: control, 55% and 70% of VO2 max exercise.  Results for state anxiety supported Solomon's theory accounting for differences in affective responding due to exercise history and exercise intensity.  For negative affect responding, Solomon's theory was strongly influenced by neuroticism.  Davidson's framework received only partial support.  The unique findings concerning the impact on neuroticism are discussed in terms of Gray's (1987) theorized neuronal systems: the behavioral activation system (BAS) and the behavioral inhibition system (BIS).  The present investigation extended past research by improving on existing methodologies regarding both Solomon's and Davidson's theories and by uniquely investigating the impact of personality dispositions on the exercise-affect relationship.