State mindfulness during physical activity moderates cognitive fusion linking intolerance of uncertainty to bedtime procrastination in university students

Bedtime procrastination is a common nighttime behavioral problem among university students. Grounded in the psychological flexibility framework and the cognitive model of insomnia, this study examined the association between intolerance of uncertainty and bedtime procrastination among university students, with particular attention to the mediating role of cognitive fusion and the moderating role of state mindfulness during physical activity. A cross-sectional survey was conducted in February 2026 using cluster sampling among 1,912 university students. The Intolerance of Uncertainty Scale-12 (IUS-12), Cognitive Fusion Questionnaire (CFQ-7), State Mindfulness Scale for Physical Activity-2 Short Form (SMS-PA-2), and Bedtime Procrastination Scale (BPS) were used to assess the core variables. Descriptive statistics and confirmatory factor analysis were conducted in SPSS 26.0 and AMOS 26.0, and statistical mediation and moderation were estimated with the PROCESS macro (Models 4 and 14). Intolerance of uncertainty was significantly positively correlated with cognitive fusion and bedtime procrastination. Statistical mediation analysis yielded a significant indirect association involving cognitive fusion, while the direct association between intolerance of uncertainty and bedtime procrastination was non-significant after cognitive fusion was included in the model. State mindfulness during physical activity significantly moderated the positive association between cognitive fusion and bedtime procrastination. Simple slope analysis showed that the positive cognitive fusion–bedtime procrastination association was smaller at higher levels of state mindfulness during physical activity. Higher intolerance of uncertainty was associated with greater bedtime procrastination, with a significant statistical indirect association involving cognitive fusion. Higher state mindfulness during physical activity was associated with a smaller positive cognitive fusion–bedtime procrastination slope. These findings are cross-sectional and should not be interpreted as evidence of temporal mediation, causal buffering, or intervention effects.