| Adequate oxygen supply is essential to maintain normal brain function,and brain oxygenation level is an important indicator of oxygen metabolism in brain tissue.Reduced oxygenation in the prefrontal cortex(PFC),the supreme command center in the brain,is closely related to human cognitive activities(i.e.,attention,memory,executive functions),and can lead to reduced cognitive function,such as slower reaction time,reduced attentional control and memory,as well as mood disorders,causing some degree of damage to the physical and mental health of all ages.Therefore,understanding ways to boost PFC oxygenation is essential to enhance PFC function,promote health,and improve quality of life and work.Numerous studies have demonstrated that aerobic exercise is a protective strategy to promote brain health in different age groups.Acute exercise transiently enhances cognitive function,while long-term exercise alters individuals’ baseline neurochemical levels and causes structural/anatomical and physiological changes.Studies have focused on the following two aspects: firstly,maximum incremental exercise was used to examine the changes in PFC oxygenation with increasing exercise intensity,to discover trends in PFC oxygenation during increasing exercise loads,find key fatigue inflection points,and to explore neurophysiological factors that affect exercise performance.It was found that PFC oxygenation gradually increased from low intensity to high intensity;after exceeding high intensity,PFC oxygenation gradually decreased compared to baseline and was lower than baseline level at exhaustion.Second,the effects and neural mechanisms of acute exercise on cognitive performance were investigated.It was found that acute aerobic exercise could transiently enhance subsequent cognitive performance and accompany increased PFC activation.However,few studies have used constant-intensity exercise to examine differences in the dynamic effects of different intensities on PFC oxygenation.Little attention has been paid to the question of whether the choice of different constant intensities has a differential effect on the enhancement of PFC oxygenation when individuals perform aerobic exercise.In addition,constant-intensity exercise is commonly used to assess the psychophysiological response during exercise.Monitoring PFC oxygenation,heart rate,and rating of perceived exertion(RPE)during exercise at a given intensity can help identify the correspondence between cerebral oxygenation and psychophysiological load.This study aimed to investigate whether the real-time PFC oxygenation response induced by constant-intensity aerobic exercise is related to the intensity of exercise and to investigate the cognitive neural mechanisms underlying it in conjunction with heart rate and PRE measurements.When selecting exercise intensity,health guidelines have traditionally recommended moderate-intensity continuous training(MICT)to maintain health in the general population.However,recent research has found that higher-intensity exercise with more significant physiological challenges can provide additional benefits,including more effective improvements in cardiorespiratory and cardiovascular function and significant increases in levels of multiple neurotransmitters.Vigorous-intensity exercise can be achieved through intervals,and aerobic vigorous-intensity interval training(VIIT)has received increasing attention in recent years.However,only some studies have examined the differences in the effects of VIIT and MICT on PFC oxygenation.In this study,we used two popular forms of fixed-intensity aerobic exercise,power cycling VIIT and MICT,and used portable wireless fNIRS technology to monitor the dynamic changes in PFC oxygenation levels throughout the exercise,comparing the differences in PFC Voxygenation between the VIIT exercise sprint and recovery phases and the corresponding MICT exercise phases,and combining the heart rate and subjective exertion levels corresponding to each exercise phase according to the function of activated brain regions measurements and reported values of subjective exertion level to explore the mechanisms that induce this response pattern.The aim was to identify differences in the effects of aerobic exercise of different intensities on PFC oxygenation,to provide neuroscientific evidence that aerobic exercise enhances PFC oxygenation and improves cognitive function,and to allow for an attempt to refine an exercise regimen.Methods: The experiment used a randomized crossover design in which 34 subjects(21males,21.14 ± 4.07 years;13 females,21.08 ± 3.50 years)were randomly divided into two groups of 17 each,and the two groups completed the VIIT or MICT task separately in the first week,and the group members completed the other exercise task in the same order in the second week.The VIIT exercise protocol consisted of the following phases: 5 minutes of rest;a total of40 minutes of exercise,including a warm–up phase(intensity of 40–60% reserve heart rate[HRR])for 10 minutes,an interval exercise(75–85% HRR)phase for 4 minutes each,for a total of 4 sessions,interspersed with three 3–minute recovery phases(30–60% HRR HRR),and a recovery time of 5 minutes after the completion of the last interval exercise.The MICT exercise protocol consisted of the following phases: 5 minutes of rest;45 minutes of exercise,with the first 5 minutes being the warm–up phase and the last 40 minutes being the exercise phase,all set at 40–60% HRR.fNIRS equipment was used to monitor the PFC oxygenation signal during the rest and exercise phases,and RPE and heart rate were measured in the last30 seconds of each exercise and recovery phase.Results:(1)for the whole PFC(all 20 channels),only two exercise phases exhibited significant differences in oxygenation signals between VIIT and MICT.After dividing the channels with significant differences between the two exercise modalities into lateral prefrontal cortex(LPFC)and frontopolar cortex(FPC)based on their function,we found that oxygenation signals in these two subregions showed more phases with significant differences between the exercise modalities.First,LPFC oxygenation levels were significantly higher in all exercise phases of VIIT than in the corresponding MICT phases and significantly lower in most recovery phases of VIIT than in the corresponding MICT phases;second,oxygenation signals in the frontopolar cortex(FPC)were significantly higher in two exercise phases of VIIT than in the corresponding MICT phases.In LPFC,the dorsolateral prefrontal cortex(DLPFC)area was activated to the largest extent,including five channels;the ventral lateral prefrontal cortex(VLPFC)area was activated to 2 channels.(2)Pairwise comparisons between motor phases in VIIT and MICT revealed that during VIIT,the PFC oxygenation signal was significantly higher than that of the resting state in all exercise phases.There were no significant differences between any two phases of MICT.(3)The correlations between RPE,Hb O(LPFC,FPC,and PFC),and heart rate were all higher in VIIT than they were in MICT.(4)RPE scores and heart rate measurements were significantly higher for each exercise phase of VIIT than for the corresponding MICT phase.However,there was almost no difference between the recovery phase of VIIT and the corresponding MICT.Conclusion: VIIT better modulates the PFC oxygenation signal than MICT,of which LPFC contributes the most.The mechanism may be that aerobic vigorous–intensity exercise requires more self–regulation than moderate–intensity exercise.Individuals need to exert a higher level of cognitive self–control,specifically attentional control(mainly associated with DLPFC)and inhibitory control(mainly associated with VLPFC).Since the DLPFC,which is primarily responsible for attentional control,is activated in a more vast and dominant region,we further speculate that the most crucial reason for VIIT’s better ability to regulate PFC oxygenation may be that high levels of attentional control induce increased neural activation of the DLPFC,which consequently elevates oxygenation levels in local brain regions. |
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