Stressed out! Not working out? Relationship between momentary stress and physical (in)activity across different time...

Stress is frequently cited as a barrier to physical activity, yet evidence from daily life remains inconclusive and may depend on the stress aspect (perceived stress, physiology), physical activity indicator (e.g., steps, vigorous activity), and temporal window studied. We investigated associations between multiple momentary stress aspects and subsequent physical activity across several time lags in daily life. Seventy-six adults in weight loss maintenance participated in a 7-day ecological momentary assessment study. Participants completed hourly smartphone surveys assessing perceived stress and safety and wore a chest-mounted sensor to derive vagally-mediated heart rate variability (vmHRV), steps, and time spent in physical inactivity, light physical activity (LPA), and moderate-to-vigorous physical activity (MVPA). Multilevel two-part models estimated within-person associations between stress and occurrence and amount of physical activity at 10-, 30-, 60-, and 120-min lags. Within-person associations between stress indicators and subsequent physical activity were often non-significant, varied across time lags and physical activity indicators but were consistent across stress aspects in direction. When significant, higher stress was associated with a small increase in subsequent physical activity, particularly steps and for shorter time lags. Significant associations for physical inactivity were largely restricted to vmHRV, indicating that activity in stress-related physiology related to higher probability of engaging in physical activity. While the results for vmHRV largely converged with those for perceived stress, it also revealed additional associations, highlighting complementary information across stress aspects. Together, these findings emphasize the value of multimodal stress assessments and time-lagged analyses for understanding how stress relates to physical activity in everyday life.