Modeling longitudinal variation in affective response to exercise across a 16-week randomized control trial (RCT).

Objective: Consistent with the Science of Behavior Change (SOBC) experimental medicine approach, this early phase intervention development study examines the influence of an intervention strategy (exercise training) on a behavioral health outcome (exercise engagement) in the service of addressing a widespread threat to public health (physical inactivity). Method: Physically inactive participants (N = 201) were randomly assigned to one of four exercise training conditions fully crossed on intensity (moderate, vigorous) and duration (short, long). Training occurred over 16-weeks and in-bout assessments of affective response (valence) and ratings of perceived exertion (RPE) were collected during Weeks 1, 4, 8, and 16. Cardiorespiratory fitness (VO₂max) was assessed pre- or postintervention and exercise behavior was assessed at 6-months postintervention follow-up. Results: Across conditions, affective response to exercise did not change, on average, over 16-weeks. Conversely, RPE decreased slightly, on average, over time. Participants completing vigorous intensity exercise reported more negatively valenced affective response and higher RPE, on average, across weeks. Greater total exercise volume completed and greater change in VO₂max were associated with more negatively valenced affective response, on average. Baseline affective response scores were positively associated with exercise minutes at follow-up; however, average affective response scores across the intervention were not associated with minutes of exercise at follow-up. Conclusions: Affective response to exercise did not become more positive in valence over time as a function of training volume or change in VO₂max. Implications for translating these findings to inform future intervention development efforts are discussed. (PsycInfo Database Record (c) 2020 APA, all rights reserved).