Post-Exercise Cognition and Prefrontal Hemodynamic Responses in Athletes: An Investigation of Low vs. High Glycemic Index Breakfast

Background/Objectives: This study aimed to investigate the effects of low and high glycemic index (LGI and HGI) breakfasts on post-exercise cognitive functions and prefrontal hemodynamic responses. Methods: Ten male athletes aged 18–22 years participated in this study. The athletes conducted two laboratory visits in a randomized manner. Athletes were given different glycemic index (GI) levels (low and high) for pre-exercise meals on different days, with the same calorie values, carbohydrate, and fat content. A total of 90 min after breakfast, a 30 min submaximal exercise was performed using a cycling ergometer. During the laboratory visits, blood glucose measurements were performed at the 0th (fasting), 90th (pre-exercise), and 120th (post-exercise) min. Additionally, the “3-Back test” was performed pre- and post-exercise to assess working memory and their prefrontal hemodynamic responses were monitored via functional Near-Infrared Spectroscopy. The collected data were evaluated in the SPSS 22 statistical program. Results: The HGI breakfast led to higher blood glucose levels at the 90th (pre-exercise) and 120th min (post-exercise) than LGI breakfast (p < 0.05). No difference was observed between HGI and LGI breakfasts in the results of the “3-Back Test” performed pre- and post-exercise. In terms of prefrontal hemodynamic responses, no difference was observed in post-exercise oxy-hemoglobin responses between the conditions. Conclusions: The findings of the study indicate that an increase in the glycemic index of breakfast has the potential to affect prefrontal oxygenation responses during cognitive tasks. However, no effect of glycemic index level was observed on cognitive and hemodynamic values at the end of the exercise.