Stressed out! Not working out? Relationship between momentary stress and physical (in)activity across different time lags: An Ecological Momentary Assessment study

Background: Stress is frequently cited as a barrier to physical activity, yet evidence from daily life remains inconclusive and may depend on the specific stress aspect (perceived stress, physiology), physical (in)activity indicator (e.g., steps, vigorous activity), and temporal window examined. This study investigated associations between multiple momentary stress aspects and subsequent physical (in)activity across several time lags in daily life.Methods: Seventy-six adults in the weight loss maintenance phase who reported difficulties maintaining a balanced diet participated in a 7-day ecological momentary assessment study. Participants completed hourly smartphone surveys assessing momentary perceived stress and perceived safety and continuously wore a chest-mounted sensor to derive vagally-mediated heart rate variability (vmHRV), steps, light physical activity (LPA), moderate-to-vigorous physical activity (MVPA), and sedentary behaviour (SB). Multilevel two-part models estimated within-person associations between each stress aspect and the subsequent occurrence and amount of physical (in)activity at 10-, 30-, 60-, and 120-minute lags.Results: Within-person associations between momentary stress indicators and subsequent physical (in)activity were predominantly small and non-significant. When significant associations emerged, higher momentary stress was positively related to the amount of subsequent physical activity, particularly for steps. Significant associations for the occurrence of physical (in)activity were largely restricted to vmHRV, indicating that activation of stress-related physiology was related to a higher probability of engaging in physical activity. Results showed heterogeneity across time lags and physical activity indicators but were overall consistent across the three stress aspects in terms of the direction of the associations.Conclusions: The findings highlight that associations between momentary stress and physical (in)activity in daily life were generally small and specific to the temporal resolution, but when significant, showed a consistent directional pattern across stress aspects. Higher momentary stress was followed by short-term increases in physical activity. While vmHRV largely converged with subjective stress indicators, it also revealed additional associations, highlighting complementary information across stress measures. Together, these findings emphasize the value of multimodal stress assessments and fine-grained, time-lagged analyses for capturing stress–physical activity dynamics in everyday life.