The joint effect and hemodynamic mechanism of PA and PM_2.5 exposure on cognitive function: A randomized controlled...

While PM_2.5 has been shown to impair cognitive function, physical activity (PA) is known to enhance it. Nonetheless, considering the increased inhalation of PM_2.5 during exercise, the potential of PA to counteract the detrimental effects of PM_2.5, along with the underlying hemodynamic mechanisms, remains uncertain.

We conducted a double-blinded, randomized controlled trial among healthy young adults in Beijing, China. Ninety-three participants were randomly allocated to groups experiencing different intensities of PA interventions, and either subjected to purified or unpurified air conditions. Cognitive function was measured by the Color-Word Matching Stroop task, and the hemodynamic response was measured using functional near-infrared spectroscopy during participants performed the Stroop task both before and after the intervention. Linear mixed-effect models were used to estimate the impact of PA and PM_2.5 on cognitive function and hemodynamic response.

The reaction time for congruent and incongruent Stroop tasks improved by - 80.714 (95% CI: -136.733, -24.695) and - 105.843 (95% CI: -188.6, -23.085) milliseconds after high-intensity interval training (HIIT) intervention. PM_2.5 and HIIT had interaction effects on cognition, such that every 1 μg/m³ increase in PM_2.5 attenuated the benefits of HIIT on reaction time by 2.231 (95% CI: 0.523, 3.938) and 3.305 (95% CI: 0.791, 5.819) milliseconds for congruent and incongruent Stroop tasks. Moreover, we divided participants into high and low PM_2.5 exposure groups based on average PM_2.5 concentration (32.980 μg/m³), and found that HIIT intervention in high PM_2.5 concentration led to 69.897 (95% CI: 9.317, 130.476) and 99.269 (95% CI: 10.054, 188.485) milliseconds increased in the reaction time of congruent and incongruent Stroop, compared with the control group among low PM_2.5. Furthermore, we found a significant interaction effects of PM_2.5 and moderate-intensity continuous training (MICT) on the middle frontal gyrus (MFG) and dorsolateral superior frontal gyrus (DLPFC). PM_2.5 and HIIT had a significant interaction effect on the DLPFC.

HIIT improved cognitive function, but the cognitive benefits of HIIT were attenuated or even reversed under high PM_2.5 exposure. The activation of the DLPFC and MFG could serve as hemodynamic mechanisms to explain the joint effect of PA and PM_2.5.