Single and combined effects of environmental heat stress and physical exercise on thermoregulation, executive function, and cerebral oxygenation

Abstract

This study investigated the single and combined effects of environmental heat stress and physical exercise on executive function (EF) performance, prefrontal cortex oxygenation, thermoregulatory responses and subjective perceptions. Sixteen subjects participated in four experimental sessions: two under moderate environmental conditions (23 °C), with and without physical exercise (R23, E23), and two under hot environmental conditions (35 °C), with and without physical exercise (R35, E35). In each session, participants completed EF tasks before and after 1 h of passive rest or 45 min of moderate-intensity cycling followed by 15 min of rest. We used Δresponse time (ΔRT) and Δaccuracy (ΔACC) of EF tasks to demonstrate changes from pre to post experiment. Additionally, changes in cerebral oxygenation during EF tasks were illustrated using the Δoxygenation difference. Heat stress alone increased core temperature (T_core), mean skin temperature (T_skin), heart rate (HR), thermal sensation (TS), and rating of perceived exertion (RPE). Exercise in a hot environment further increased physiological indicators and RPE, but TS exhibited a different pattern, with lower TS in R35 compared to E35 during the second battery of executive function tests. Moreover, heat stress alone increased ΔRT for the More-Odd Shifting task and the Stroop task under incongruent conditions, while decreasing the Δoxygenation difference during the More-Odd Shifting task. ΔRT for the 2-back, More-Odd Shifting and Stroop tasks under incongruent conditions were lower in the E35 trial than in the R35 trial, whereas the Δoxygenation difference was higher in the E35 trial compared to the R35 trial. These findings indicate that environmental heat stress alone increases T_core and T_skin, alters TS, and impairs EF performance by decreasing prefrontal cortex oxygenation. A 45-min moderate-intensity exercise combined with environmental heat stress enhances the increases in body temperatures but mitigates the detrimental effects of heat stress alone on EF performance by increasing prefrontal cortex oxygenation.