Effects of physical activity intensity and task complexity on behavioral and hemodynamic responses in civilians and military personnel

Introduction: Physical activity and exercise training positively enhance cognitive performance across all age-levels. Military personnel undergo intense physical training. Currently, there is a paucity of research in this population in respect how their training may impact executive function measures. Functional near infrared spectroscopy (fNIRS) is an emerging low-cost, noninvasive neuroimaging technique sensitive enough to detect both cognitive load and state and is suitable for measuring cerebral oxygenation changes during both motor and/or cognitive behavioral tasks. The purpose of this study was to determine both behavioral and hemodynamic changes in the prefrontal cortex over varying task complexities and physical activity intensities between civilians and military personnel. Methods: Seventeen healthy individuals (age = 25.6 ± 2.3 years, BMI = 24.2 + 2.3; n= 12 male, n= 5 female, n= 6 military personnel) were recruited to participate in the study. Participants completed a cognitive battery (Erikson Flanker, Switcher, and Delayed- Match-to-Sample tasks) recording accuracy and reaction time both before and after physical activity conditions. Participants also completed six conditions of varying physical intensities (sit, stand, walk) and cognitive complexities (low: congruent; high: incongruent). During the congruent conditions, participants struck green objects, not red. During the incongruent conditions, participants struck red objects, not green. Independent sample t-tests were used to compare accuracy, reaction time, and HbO₂ concentration across physical activity conditions and pre- post-exercise cognitive tasks between Military and Civilians. Results: Physical activity conditions were validated using heart rate data. Both groups experienced significantly greater improvements in all cognitive tasks prepost-test in reaction time, with little differences between groups. Both groups also experienced improvements in both accuracy and reaction time during the physical activity conditions as the intensity increased, with little differences between groups. Higher HbO₂ concentrations during the pre-cognitive tasks relative to the post-cognitive tasks was observed, with no significant difference between groups. Discussion: fNIRS modalities are a valid measure of cerebral HbO₂ concentration changes in the prefrontal cortex before, during and after physical activity in the laboratory setting using a virtual reality system. The findings of this study need to be replicated and the methods applied to different samples of the population