Translating physical activity intentions into behavior in adults with overweight/obesity: The role of daily stressors and stress pile-up.

PURPOSE: Research shows an inconsistent association between psychological stress and physical activity (PA), which may be due to not considering the type of stress (daily stressors vs. accumulated daily stressors [i.e., stress pile-up]) and the role of PA intentions in PA behavior. This study investigated whether daily stressful experiences or stress pile-up moderate within-person associations between daily PA intentions and PA behavior. METHODS: Adults with a body mass index ≥25 kg/m2 wore an activPAL for 21 days to measure moderate-to-vigorous PA (MVPA) and completed morning diaries about PA intentions and evening diaries about stressful experiences. Two-part multilevel models tested within-person interactions between intentions, daily stress experiences and stress pile-up (stressor frequency, intensity, negative affect) across 21 days on odds and volume of MVPA. RESULTS: Participants (N = 91, Mage = 30.7 ± 6.5, 58 % female, 72 % White) experienced stressors on 32 % of days. On days with stronger intentions, participants had 49 % higher odds of doing MVPA and spent 26 % more time in MVPA (ps < 0.001). After adjusting for multiple comparisons, stress pile-up, but not daily stress experiences, moderated PA intention-behavior associations. Intentions were associated with time in MVPA when people experienced fewer than 10 stressors or stress intensity pile-up was less than 25.7 points but not when pile-up was higher (PRinteraction = 0.98 and 0.99, respectively). CONCLUSIONS: Stress pile-up undermined the translation of PA intentions into behavior. This could promote a negative reinforcement cycle with stress pile-up reducing PA participation and reduced PA exacerbating people's stress responses. Effective stress-management could interrupt this cycle to promote better health.