Habits and self-efficacy moderate the effects of intentions and planning on physical activity

Abstract

Objectives: Behavioural intentions as well as action planning can facilitate the adoption and maintenance of physical activity under certain conditions. The present study examined levels of plan-specific self-efficacy and habit strength as possible conditions that may modify this relationship. Design: As a secondary analysis of a larger randomized trial to improve physical activity, n = 225 recipients of a planning intervention were followed up at five measurement points over one year. Methods: Two-level models were fit. Within-person levels, that is, fluctuations of intention and action planning around person means, were modelled to predict self-reported moderate-to-vigorous physical activity. Moreover, between-person, that is, average person, levels of self-efficacy and habit strength were specified as putative moderators of this relationship. Results: The within-person intention–activity relationship was moderated by between-person levels of habit strength, yielding a compensatory effect: higher-than-usual intention predicted physical activity only when average activity habit levels were low. The within-person planning–activity relationship was moderated by between-person levels of self-efficacy, yielding a synergistic effect: higher-than-usual planning combined with high average self-efficacy resulted in highest physical activity levels. Conclusion: Higher-than-usual intention may only be required in the presence of low activity habits. Moreover, high self-efficacy seems to be required to translate higher-than-usual action planning into augmented physical activity because self-efficacious individuals may invest more efforts to enact their plans.