The effects of fluid loss status with high intensity interval exercise on brain hemodynamic and cognition

Fluid loss is a stress that negatively affects many aspects of human performance, especially physical, physiological and cognitive functions. Fluid loss in exercise condition has become a topic of interest in current studies. The aim of this study is to investigate the effects of exercise-induced dehydration on prefrontal cortex hemodynamics, cognitive performance and physical performance. Twelve healthy male participants (20.4 years aged, training experience 8 years) who trained regularly were included in the study. The study was carried out in two sessions, with ~ 1% hypohydration and euhydration condition. Participants were given water at a level of ~ 1% of their body weight in the euhydration session, while they were subject to fluid restriction in the hypohydration session. Body weight, heart rate and hematocrit measurements were performed at the beginning of all sessions, and then a 2-back cognitive test protocol was applied. These tests were repeated post-exercise sessions. In the first exercise sessions, participants were included in a 30-minute submaximal exercise session on a bicycle ergometer. They were subjected to modified sprint interval exercise in the second session after a 15-minute transition phase. Before and after exercise sessions, prefrontal cortex hemodynamic responses were recorded with the fNIRS method. Analysis of variance (repeated measures ANOVA) was applied for repeated measurements in the statistical analysis of the data. The statistical significance level was set at 0.05. In the intergroup comparisons, a significant difference was found between body weight, hematocrit levels, heart rate, peak power outputs and rating of perceived exertion levels (p = 0.00-0.05). There was no significant difference between the groups. As a result; It was found that ~ 1% hypohydration had a mild impairement effect on prefrontal cortex oxyhemoglobin and total hemoglobin response, reaction time, peak power outputs, and rating of percived exertion levels. This information suggests that the ~ 1 hypohydration condition is the initial threshold of impairment in human performance