Acute bouts of physical exercise have the potential to benefit children's cognition. Inconsistent evidence calls for systematic investigations of dose-response relations between quantitative (intensity and duration) and qualitative (modality) exercise characteristics. Thus, in this study the optimal duration of an acute cognitively challenging physical exercise to benefit children's cognition was investigated, also exploring the moderating role of individual characteristics. In a within-subject experimental design, 104 children (M_age = 11.5, SD = 0.8, 51% female) participated weekly in one of four exergaming conditions of different durations (5, 10, 15, 20 min) followed by an Attention Network task (ANT-R). Exergame sessions were designed to keep physical intensity constant (65% HR_max ) and to have a high cognitive challenge level (adapted to the individual ongoing performance). Repeated measures ANOVAs revealed a significant effect of exercise duration on reaction times (RTs; p = 0.009, ƞ² _p = 0.11), but not on response accuracy. Post hoc analyses showed faster information processing speed after 15 min of exercise compared to 10 min (p = 0.019, ƞ² _p = 0.09). Executive control, alerting and orienting performances and interactions were unaffected by exercise duration (p_s > 0.05). Among individual characteristics, habitual physical activity moderated duration effects on RTs. For more active children, exercise duration influenced the interaction between executive control and orienting (p = 0.034; ƞ² _p = 0.17) with best performances after the 15 min duration. Results suggest that an acute 15 min cognitively high-challenging bout of physical exercise enhances allocable resources, which in turn facilitate information processing, and-for more active children only-also executive processes. Results are interpreted according to the arousal theory and cognitive stimulation hypothesis.

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