| Objective: While brief bouts of exercise improve cognitive function, more prolonged exercise can suppress attention and executive function. Dehydration and heat exposure are known contributors to these deficits, though the role of blood sugar changes during exercise in cognitive dysfunction is less understood at this time. The current study sought to clarify the independent contribution of blood glucose levels to cognitive function following demanding exercise.;Method: Healthy adult males (N= 10, age= 21.9 +/- 1.97 years) presented for two counterbalanced experimental trials in a 100 degrees F heated chamber. Each experimental trial consisted of BASELINE glucose and cognitive function assessments, as measured by the Logical Relations (LR) and Running Memory Continuous Performance Task (RMCPT) subtests of the Automated Neuropsychological Assessment Metrics- 4th Edition (ANAM4). Participants then completed 120 minutes of exercise on a cycle ergometer, with glucose and cognitive function measured POST-EXERCISE. Next, participants rehydrated with a zero-sugar or full-sugar sports beverage, with measures of glucose and cognitive function repeated immediately POST-REHYDRATION. Finally, after a 15-minute recovery period during which the participants rested while not permitted to drink, they completed experimental measures an additional time, at POST-RECOVERY.;Results: Physiological response to the experimental trials was similar across conditions. Participants demonstrated significantly reduced blood glucose levels (F(1,9)=16.93, p<0.01) and lost an average of 2.57% of their body weight following exercise. Contrary to hypotheses, repeated measures ANOVA showed performance on LR did not change from BASELINE to POST-EXERCISE and actually declined from POST-EXERCISE to POST-REHYDRATION (F(1,9)=9.44, p=0.01). Performance on RMCPT improved from BASELINE to POST-EXERCISE (F(19)=5.43, p<0.05) and the zero-sugar condition produced gains from POST-REHYDRATION to POST-RECOVERY (F(1,9)=6.45, p=0.03) relative to the full-sugar condition.;Conclusion: Contrary to past studies, cognitive function did not universally decline with strenuous exercise, despite reduced blood glucose levels. Performances on an attention measure increased following exercise and were unexpectedly better at POST-RECOVERY for the zero- versus the full-sugar condition. However, executive functioning was stable to POST-EXERCISE and declined following rehydration. The exact mechanisms responsible for this pattern of findings are unclear, but likely involve a combination of limited core temperature increase and dehydration level, reactivity to blood sugar fluctuations, and multiple possible variables not assessed in the current study such as neurotransmitter and blood lactate levels, brain temperature, physiological arousal, and task engagement. Future studies are needed to better understand the inconsistent findings across the literature, as a significant number of individuals engage in strenuous and prolonged exercise regularly, including those involved in service positions (i.e., military personnel and firefighters). Articulating the mechanisms at play in this phenomenon may increase safety and improve performance. |
