Daytime sleepiness and academic engagement among university students: mind wandering as a partial mediator and physical activity as a limited moderator

This cross-sectional study examined whether mind wandering statistically accounted for the association between daytime sleepiness and academic engagement, and whether physical activity served as a boundary condition in this association. University students in a southern province of China, completed an anonymous online questionnaire. After prespecified quality screening, 1,377 valid responses were included in the main analyses and 1,371 complete cases were included in the moderated mediation analysis. Daytime sleepiness was associated with lower academic engagement and more frequent mind wandering. Mind wandering partially accounted for the association between daytime sleepiness and academic engagement, with an indirect effect of -0.122 (95% bootstrap CI [-0.152, -0.094]), representing approximately 31.8% of the total association. Physical activity showed a statistically detectable interaction with daytime sleepiness in relation to mind wandering (B = -0.005, p = 0.003), but the incremental explanatory value and the moderated mediation index were very small [index = 0.001; 95% bootstrap CI (0.000, 0.002)]. These findings should be interpreted as cross-sectional associations. Mind wandering appeared to be a relevant cognitive correlate within the proposed model, whereas the practical relevance of the physical activity moderation was limited and should not be interpreted as evidence of a strong buffering effect.