University students experience negative emotions due to their study situation, which adversely affects their academic performance. Previous between-group and between-individual studies have demonstrated that cognition, physical activity, and sleep serve as predictors of academic performance. The objective of this pilot study was to examine the potential relationship between physical activity, sleep, and cognition within days, as well as to explore whether physical activity and sleep have a bidirectional relationship within days. This observational study consisted of five N-of-1 studies involving university students aged 22-29. Physical activity levels were measured using accelerometers, while cognition was assessed using the memory span test within the m-Path app. Sleep quality and duration were self-assessed through the ecological momentary assessment approach within the m-Path app. The study did not yield statistically significant findings. It is important to note that the study's methodological choices may have hindered the detection of potentially significant associations and effects. Future studies should employ more objective measurement methods, increase the number of measurement occasions, and include a more diverse sample group in order to further investigate these relationships.