Regular physical activity is associated with physical and mental health benefits, yet many adults fail to meet recommended activity levels. This study examined the role of affect in shaping exercise intentions, drawing on the Affective Gradient Hypothesis, which proposes that expected affective consequences guide motivated behaviour. Using a randomized between-subjects design, 285 university students were assigned to a positive, negative, or neutral affect induction, involving a scenario-based imagination task related to exercising. Positive and negative affect were assessed before and after the induction, and exercise intentions were measured as the outcome. Mediation analyses tested whether post-induction positive and negative affect explained the relationship between the affect induction and exercise intentions.

Results showed that the induction significantly lowered positive affect in the negative group, but did not significantly increase positive affect in the positive group, and it had no effect on negative affect. Nonetheless, higher positive affect was associated with stronger exercise intentions. A significant indirect effect emerged for the negative condition, whereby lower positive affect was linked to weaker exercise intentions. In contrast, the exploratory analysis found no evidence that negative affect mediated this relationship. These findings suggest that affect, especially positive affect, plays an important role in shaping exercise intentions.