Contextual and affective precursors of physical activity intention and enactment examined through ecological momentary assessment.

Background: Regular physical activity (PA) provides numerous health benefits, which is why many people intend to lead an active lifestyle. Yet, internal and external states and barriers can hinder the translation of such intentions into actual behavior. This study prospectively studied such barriers, namely, the temporal relationship between the independent variables momentary affect (stress, emotions), and the dependent variables PA intentions and subsequent PA behavior. The variables were measured using Ecological Momentary Assessment (EMA) at the within-person level.

Methods: A total of 41 healthy participants (aged 19-67) completed 4 daily EMA prompts over three weeks on their smartphones, capturing data on momentary affective states (happy, active, irritated, tired, concerned, nervous, relaxed, energetic), anticipated contextual barriers (i.e., PA-incompatible external circumstances), prospective PA intentions, and PA behavior (retrospective, since the last prompt). We applied generalized linear mixed effect models to examine the influence of momentary affect and contextual barriers onto a) PA intentions, b) their consecutive enactment, and c) directly onto PA behavior.

Results: Individuals were more likely to form PA intentions when feeling happy, active, or energetic, but less likely when external/contextual barriers were high or when they felt tired. Furthermore, only PA intentions were significant precursors of subsequent PA behavior, while neither contextual barriers, nor momentary affect directly affected PA behavior.

Conclusions: Interventions for fostering PA, such as Just-in-Time Adaptive Interventions, should address and 'stabilize' intentions through addressing external barriers and positive affects (happy, active, energetic). The present results call for more temporally sensitive and dynamic health behavior theories of PA.