Cardiorespiratory fitness moderates the effect of an affect-guided physical activity prescription: a pilot randomized controlled trial.

Physical activity (PA) interventions have a clear role in promoting mental health. Current PA guidelines directed toward specific PA intensities may have negative effects on affective response to exercise, and affective response is an important determinant of PA adherence. In this randomized trial of 67 previously inactive adults, we compared the effects of a PA prescription emphasizing the maintenance of positive affect to one emphasizing a target heart rate, and tested the extent to which the effect of the affect-guided prescription on PA is moderated by cardiorespiratory fitness (CRF). We found the effect of an affect-guided prescription was significantly moderated by CRF. At one week, for participants with lower CRF (i.e. poor conditioning), the affect-guided prescription resulted in significantly greater change in PA minutes (M = 240.8) than the heart rate-guided prescription (M = 165.7), reflecting a moderate-sized effect (d = .55). For those with higher CRF (i.e. good conditioning), the means were in the opposite direction but not significantly different. At one month, the same pattern emerged but the interaction was not significant. We discuss the implications of these findings for the type of PA prescriptions offered to individuals in need.