Self-regulatory moderators of the intention–behavior gap in physical activity: an ecological momentary assessment study among young adults

Physical activity (PA) intentions do not always translate into behavior, particularly at the momentary level, producing a well-documented intention–behavior gap; yet it remains unclear whether self-regulatory factors explain for whom and when intention–PA coupling is stronger or weaker. This study examined whether time-invariant self-regulatory traits (behavioral inhibition system/behavioral activation system sensitivity, trait self-control, and PA self-regulatory strategies) and time-varying momentary states (feeling focused, feeling in control, procrastinating) moderate the within-day association between momentary PA intentions and subsequent accelerometer-measured PA among young adults. Participants ( N = 228; ages 18–29) completed hourly, signal-contingent mobile ecological momentary assessment (EMA) surveys assessing intentions for PA in the next 60 min across 4-day monitoring periods repeated over 12 months, paired with wrist-worn accelerometer measuring movement intensity (20,491 observations). Multilevel Gamma models decomposed intention and moderator variables into between-person (BP) and within-person (WP) components. Within-person intention consistently predicted greater subsequent movement in the 60 min following each EMA prompt ( p ≤ 0.002) in 13 of 14 models. Seven of 14 moderators produced a significant interaction at p < 0.01, one term from each of seven moderator constructs. Trait behavioral inhibition, PA self-monitoring, and time management moderated the BP intention–PA association, indicating for whom a higher overall rate of intending translated into greater activity. Social support and self-reinforcement moderated the WP intention–PA association, indicating for whom momentary intentions more strongly predicted subsequent activity. Momentary focus moderated the WP association at the occasion level, indicating when within a person intentions were more predictive, and momentary procrastination moderated the BP association. All seven effects were compensatory rather than augmenting: The intention–PA association was strongest among individuals lower in self-regulatory capacity and, for the momentary states, on occasions when a person's capacity was lower than usual. These findings suggest that momentary intentions may serve as an alternative route to activity when self-regulatory capacity is low. Just-in-time intervention strategies that support the formation of momentary intentions among individuals and moments of greatest self-regulatory vulnerability may be useful for improving PA.