Social-cognitive theories, such as the theory of planned behavior, posit intentions as proximal influences on physical activity (PA). This paper extends those theories by examining within-person variation in intentions and moderate-to-vigorous physical activity (MVPA) as a function of the unfolding constraints in people’s daily lives (e.g., perceived time availability, fatigue, soreness, weather, overeating). College students (N = 63) completed a 14-day diary study over the Internet that rated daily motivation, contextual constraints, and MVPA. Key findings from multilevel analyses were that (1) between-person differences represented 46% and 33% of the variability in daily MVPA intentions and behavior, respectively; (2) attitudes, injunctive norms, self-efficacy, perceptions of limited time availability, and weekend status predicted daily changes in intention strength; and (3) daily changes in intentions, perceptions of limited time availability, and weekend status predicted day-to-day changes in MVPA. Embedding future motivation and PA research in the context of people’s daily lives will advance understanding of individual PA change processes.
David E. Conroy is with the Department of Kinesiology and with the Department of Human Development and Family Studies; Steriani Elavsky is with the Department of Kinesiology; Shawna E. Doerksen is with the Department of Recreation, Park, and Tourism Management; and Jaclyn P. Maher is with the Department of Kinesiology, all at Pennsylvania State University, University Park, Pennsylvania.