Can In-Task Affect During Interval and Continuous Exercise Predict 12-Month Physical Activity Behavior? Findings from a Randomized Trial

Background In-task affective responses to moderate-intensity continuous exercise training (MICT) have been shown to predict future physical activity behavior. However, limited research has investigated whether this affect–behavior relationship is similar for high-intensity interval training (HIIT) and whether it holds true over the longer term. This study aims to determine (1) if in-task affect during 2 weeks of supervised MICT and HIIT predicted changes to unsupervised moderate-to-vigorous physical activity (MVPA) behavior 12 months post-intervention and (2) if this predictive relationship was moderated by exercise type (MICT vs. HIIT). Method Ninety-nine adults (69.7% female; 50.9 ± 9.4 years) who were low active and overweight were randomized to 2 weeks of exercise training of MICT ( n = 52) or HIIT ( n = 47), followed by 12 months of accelerometry-assessed free-living MVPA. Results The pooled moderation model was not significant, F (3, 94) = 2.54, p = .07 ( R 2 = 0.085), with a non-significant group by affect interaction ( p = .06). The conditional effect for MICT was significant ( B = 17.27, t = 2.17, p = .03), suggesting that 12-month change in MVPA increased by 17.27 min/week for every one-point increase in in-task affect. The conditional effect for HIIT was not significant ( p = .85), suggesting that in-task affect was not predictive of 12-month change in MVPA. Conclusion The current findings raise important questions about whether the affect–behavior relationship may vary depending on exercise type. For HIIT-based exercise in particular, additional psychological constructs beyond in-task affect should be considered when attempting to predict future physical activity behavior.