The effects of exercise under hypoxia on cognitive function

Effects of Exercise Training Under Hypoxia Versus Normoxia on Cognitive Function in Clinical and Non-Clinical Populations: A Systematic Review and Meta-analysis

OBJECTIVE

To compare the effects of exercise training under hypoxia versus normoxia on cognitive function in clinical and non-clinical populations.

DATA SOURCES

From inception to June 13th, 2022, a systematic search was performed on PubMed, Web of Science, Embase, Scopus, and Cochrane Central Register of Controlled Trials.

STUDY SELECTION

Randomized controlled trials comparing the effects of exercise under hypoxic vs normoxic on cognition in clinical and non-clinical populations were included. The systematic search generated 14,894 relevant studies, of which 12 were finally included.

DATA EXTRACTION

Two reviewers independently extracted data from included studies. Results were expressed as standardized mean difference (SMD). Each included study was assessed using the Cochrane Risk of Bias 1.0 (RoB1.0) tool. Finally, the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) system was used to rate the certainty of evidence for each outcome.

DATA SYNTHESIS

Overall, 12 studies with a total of 338 participants met the inclusion criteria. The pooled results suggested that hypoxia exercise had a small but not statistically significant positive effect on overall cognitive function (SMD=0.064, 95% confidence interval (CI): -0.156-0.284, P=.567, very low-certainty evidence), when compared with normoxic exercise. Regarding the domain-specific cognitive functions, there was a medium and significant positive effect on memory (SMD=0.594, 95% CI: 0.068 to 1.120, P=.027, very low-certainty evidence), while effects on visuospatial function (SMD=0.490, 95% CI: -0.030 to 1.010, P=.065, very low-certainty evidence), attention (SMD=0.037, 95% CI: -0.340 to 0.414, P=.847, very low-certainty evidence), executive function (SMD=0.096, 95% CI: -0.268 to 0.460, P=.605, very low-certainty evidence), and processing speed (SMD=-0.145, 95% CI: -0.528 to 0.239, P=.459, very low-certainty evidence) were not statistically significant.

CONCLUSIONS

The current pooled results revealed that hypoxic exercise was related to improved cognitive performance. Nevertheless, exercise under hypoxia did not have a significant advantage in cognitive promotion when compared with exercise under normoxia.

Immediate effect of physical activity on the autonomic nervous system in individuals with autism spectrum disorders of different age groups: a randomised trial

Background

Autism spectrum disorder (ASD) is one of the most complex neurodevelopmental disorders. It affects almost all human physiological systems. Individuals with ASD often display dysregulation in their autonomic nervous system (ANS), which may elicit differing effects across age groups. Also, studying the ANS missed several important parameters related to ANS. Studying the ANS is crucial in developing adaptive behavioural strategies and maintaining communication abilities and social behaviours. Thus, this study compared the immediate effect of physical activity on the ANS in individuals with ASD in different age groups.

Methods

200 participants (106 males and 94 females) took part in a double-blinded randomised design. All participants were divided into four groups according to their age (4-7, 7-10, 10-13 and 14-18 years old). Participants performed a 60 min treadmill walk. The main outcome measurements were heart rate (HR), saturation of peripheral oxygen (SpO2), respiratory rate (RR) and end-tidal carbon dioxide (etCO2).

Results

Before the study, there were non-significant differences between groups in their physical characteristics (body mass index, Childhood Autism Rating Scale, physical activity level, both parents' existence, aerobic capacity and gender) (p>0.05). At baseline measurements, there were non-significant differences between all groups for all outcome measurements (p>0.05). Immediately after physical activity, there was significant difference between group 1 and other groups (p<0.05), while all other differences were non-significant (p>0.05). At the follow-up (after 15 min of rest), group 1 maintained significant differences with the other groups for all outcome measurements (p<0.05), while there were non-significant differences between the other three groups (p>0.05).

Conclusion

This study revealed that the SpO2 significantly decreased immediately after the physical activity, while HR, RR and etCO2 significantly increased immediately after physical activity in comparison to the baseline measurements. Contrary to other ANS parameters (SpO2, RR and etCO2), HR in early ages (4-7 years old) was higher after physical activity and remained elevated longer than other ages. The early ages (4-7 years old) take more time to return to the normal status of ANS parameters including SpO2, HR, RR and etCO2.

Trial registration number

NCT05725733.

Simulated Acute Hypobaric Hypoxia Effects on Cognition in Helicopter Emergency Medical Service Personnel - A Randomized, Controlled, Single-Blind, Crossover Trial

OBJECTIVE

To evaluate, under replicable, blinded and standardised conditions, the effect of acute exposure to hypobaric hypoxia (HH) (equivalent to 200 or 3000 or 5000 m above sea level (asl)) on selected cognitive domains and physiological parameters in personnel of helicopter emergency medical service (HEMS).

METHODS

We conducted a randomized clinical trial using a single-blind crossover design in an environmental chamber (terraXcube) to induce HH in 48 HEMS personnel. Participants performed cognitive tests (CT) before the ascent, after 5 min at altitude, and after simulated cardiopulmonary resuscitation (SCR). CT evaluated: sustained attention using the psychomotor vigilance test (PVT) that included measurement of reaction time (RT); risky decision making using the balloon analogue risk task (BART), and attention and speed of processing using the digit symbol substitution test (DSST). CT performance was subjectively rated with a visual analogue scale (VAS). Physiological data were recorded with a physiological monitoring system. Data were analysed using a linear mixed model and correlation analysis.

RESULTS

Mean reaction time was significantly slower (p = 0.002) at HH (5000 m asl), but there were no independent effects of HH on the other parameters of the PVT, BART or DSST. Participants did not detect subjectively the slower RT at altitude since VAS performance results showed a positive correlation with mean RT (p = 0.009). DSST results significantly improved (p = 0.001) after SCR.

CONCLUSION

Acute exposure of HEMS personnel to HH induced a slower RT but no changes in any other investigated measures of cognition. The reduced RT was not detected subjectively by the participants. Trial number 3489044136, ClinicalTrials.gov trial registration.

The effects of sleep deprivation, acute hypoxia, and exercise on cognitive performance: A multi-experiment combined stressors study

INTRODUCTION

Both sleep deprivation and hypoxia have been shown to impair executive function. Conversely, moderate intensity exercise is known to improve executive function. In a multi-experiment study, we tested the hypotheses that moderate intensity exercise would ameliorate any decline in executive function after i) three consecutive nights of partial sleep deprivation (PSD) (Experiment 1) and ii) the isolated and combined effects of a single night of total sleep deprivation (TSD) and acute hypoxia (Experiment 2).

METHODS

Using a rigorous randomised controlled crossover design, 12 healthy participants volunteered in each experiment (24 total, 5 females). In both experiments seven executive function tasks (2-choice reaction time, logical relations, manikin, mathematical processing, 1-back, 2-back, 3-back) were completed at rest and during 20 min semi-recumbent, moderate intensity cycling. Tasks were completed in the following conditions: before and after three consecutive nights of PSD and habitual sleep (Experiment 1) and in normoxia and acute hypoxia (FIO2 = 0.12) following one night of habitual sleep and one night of TSD (Experiment 2).

RESULTS

Although the effects of three nights of PSD on executive functions were inconsistent, one night of TSD (regardless of hypoxic status) reduced executive functions. Significantly, regardless of sleep or hypoxic status, executive functions are improved during an acute bout of moderate intensity exercise.

CONCLUSION

These novel data indicate that moderate intensity exercise improves executive function performance after both PSD and TSD, regardless of hypoxic status. The key determinants and/or mechanism(s) responsible for this improvement still need to be elucidated. Future work should seek to identify these mechanisms and translate these significant findings into occupational and skilled performance settings.

The neuromodulatory role of dopamine in improved reaction time by acute cardiovascular exercise

Acute cardiovascular physical exercise improves cognitive performance, as evidenced by a reduction in reaction time (RT). However, the mechanistic understanding of how this occurs is elusive and has not been rigorously investigated in humans. Here, using positron emission tomography (PET) with [11 C]raclopride, in a multi-experiment study we investigated whether acute exercise releases endogenous dopamine (DA) in the brain. We hypothesized that acute exercise augments the brain DA system, and that RT improvement is correlated with this endogenous DA release. The PET study (Experiment 1: n = 16) demonstrated that acute physical exercise released endogenous DA, and that endogenous DA release was correlated with improvements in RT of the Go/No-Go task. Thereafter, using two electrical muscle stimulation (EMS) studies (Experiments 2 and 3: n = 18 and 22 respectively), we investigated what triggers RT improvement. The EMS studies indicated that EMS with moderate arm cranking improved RT, but RT was not improved following EMS alone or EMS combined with no load arm cranking. The novel mechanistic findings from these experiments are: (1) endogenous DA appears to be an important neuromodulator for RT improvement and (2) RT is only altered when exercise is associated with central signals from higher brain centres. Our findings explain how humans rapidly alter their behaviour using neuromodulatory systems and have significant implications for promotion of cognitive health. KEY POINTS: Acute cardiovascular exercise improves cognitive performance, as evidenced by a reduction in reaction time (RT). However, the mechanistic understanding of how this occurs is elusive and has not been rigorously investigated in humans. Using the neurochemical specificity of [11 C]raclopride positron emission tomography, we demonstrated that acute supine cycling released endogenous dopamine (DA), and that this release was correlated with improved RT. Additional electrical muscle stimulation studies demonstrated that peripherally driven muscle contractions (i.e. exercise) were insufficient to improve RT. The current study suggests that endogenous DA is an important neuromodulator for RT improvement, and that RT is only altered when exercise is associated with central signals from higher brain centres.

Acute hypoxia impairs posterior cerebral bioenergetics and memory in man

Hypoxia has the potential to impair cognitive function; however, it is still uncertain which cognitive domains are adversely affected. We examined the effects of acute hypoxia (∼7 h) on central executive (Go/No-Go) and non-executive (memory) tasks and the extent to which impairment was potentially related to regional cerebral blood flow and oxygen delivery (CDO2 ). Twelve male participants performed cognitive tasks following 0, 2, 4 and 6 h of passive exposure to both normoxia and hypoxia (12% O2 ), in a randomized block cross-over single-blinded design. Middle cerebral artery (MCA) and posterior cerebral artery (PCA) blood velocities and corresponding CDO2 were determined using bilateral transcranial Doppler ultrasound. In hypoxia, MCA DO2 was reduced during the Go/No-Go task (P = 0.010 vs. normoxia, main effect), and PCA DO2 was attenuated during memorization (P = 0.005 vs. normoxia) and recall components (P = 0.002 vs. normoxia) in the memory task. The accuracy of the memory task was also impaired in hypoxia (P = 0.049 vs. normoxia). In contrast, hypoxia failed to alter reaction time (P = 0.19 vs. normoxia) or accuracy (P = 0.20 vs. normoxia) during the Go/No-Go task, indicating that selective attention and response inhibition were preserved. Hypoxia did not affect cerebral blood flow or corresponding CDO2 responses to cognitive activity (P > 0.05 vs. normoxia). Collectively, these findings highlight the differential sensitivity of cognitive domains, with memory being selectively vulnerable in hypoxia. NEW FINDINGS: What is the central question of this study? We sought to examine the effects of acute hypoxia on central executive (selective attention and response inhibition) and non-executive (memory) performance and the extent to which impairments are potentially related to reductions in regional cerebral blood flow and oxygen delivery. What is the main finding and its importance? Memory was impaired in acute hypoxia, and this was accompanied by a selective reduction in posterior cerebral artery oxygen delivery. In contrast, selective attention and response inhibition remained well preserved. These findings suggest that memory is selectively vulnerable to hypoxia.

Hemiplegia resulting from acute carbon monoxide poisoning

Carbon monoxide (CO) poisoning can cause neurological complications such as movement disorders and cognitive impairment through hypoxic brain damage. Although peripheral neuropathy of the lower extremities is a known complication of CO poisoning, hemiplegia is very rare. In our case, a patient who developed left hemiplegia due to acute CO poisoning received early hyperbaric oxygen treatment (HBOT). The patient had left hemiplegia and anisocoria at the beginning of HBOT. Her Glasgow coma score was 8. A total of five sessions of HBOT at 243.2 kPa for 120 minutes were provided. At the end of the 5th session, the patient's hemiplegia and anisocoria were completely resolved. Her Glasgow coma score was 15. After nine months of follow-up, she continues to live independently with no sequelae, including delayed neurological sequelae. Clinicians should be aware that CO poisoning can (rarely) present with hemiplegia.

The brain in motion-cognitive effects of simultaneous motor activity

During the last 30 years, a large number of behavioral studies have investigated the effect of simultaneous exercise on cognitive functions. The heterogeneity of the results has been attributed to different parameters, such as intensity or modality of physical activity, and the investigated cognitive processes. More recent methodological improvements have enabled to record electroencephalography (EEG) during physical exercise. EEG studies combining cognitive tasks with exercise have described predominantly detrimental effects on cognitive processes and EEG parameters. However, differences in the underlying rationale and the design of EEG versus behavioral studies make direct comparisons between both types of studies difficult. In this narrative review of dual-task experiments we evaluated behavioral and EEG studies and discuss possible explanations for the heterogeneity of results and for the discrepancy between behavioral and EEG studies. Furthermore, we provide a proposal for future EEG studies on simultaneous motion to be a useful complement to behavioral studies. A crucial factor might be to find for each cognitive function the motor activity that matches this function in terms of attentional focus. This hypothesis should be investigated systematically in future studies.

Anodal tDCS over the left DLPFC but not M1 increases muscle activity and improves psychophysiological responses, cognitive function, and endurance performance in normobaric hypoxia: a randomized controlled trial

BACKGROUND

Transcranial direct current stimulation (tDCS) has been shown to have positive effects on exercise performance and cognitive function in the normal ambient condition. Hypoxia is deemed a stressful situation with detrimental effects on physiological, psychological, cognitive, and perceptual responses of the body. Nevertheless, no study has evaluated the efficacy of tDCS for counteracting the negative effects of hypoxic conditions on exercise performance and cognition so far. Hence, in the present study, we investigated the effects of anodal tDCS on endurance performance, cognitive function, and perceptual responses in hypoxia.

PARTICIPANTS AND METHODS

Fourteen endurance-trained males participated in five experimental sessions. After familiarization and measuring peak power output in hypoxia, in the first and second sessions, through the 3rd to 5th sessions, participants performed a cycling endurance task until exhaustion after 30 min hypoxic exposure at resting position followed by 20 min of anodal stimulation of the motor cortex (M1), left dorsolateral prefrontal cortex (DLPFC), or sham-tDCS. Color-word Stroop test and choice reaction time were measured at baseline and after exhaustion. Time to exhaustion, heart rate, saturated O₂, EMG amplitude of the vastus lateralis, vastus medialis, and rectus femoris muscles, RPE, affective response, and felt arousal were also measured during the task under hypoxia.

RESULTS

The results showed a longer time to exhaustion (+ 30.96%, p₌0.036), lower RPE (- 10.23%, p ₌ 0.045) and higher EMG amplitude of the vastus medialis muscle (+ 37.24%, p₌0.003), affective response (+ 260%, p₌0.035) and felt arousal (+ 28.9%, p₌0.029) in the DLPFC tDCS compared to sham. The choice reaction time was shorter in DLPFC tDCS compared to sham (- 17.55%, p₌0.029), and no differences were seen in the color-word Stroop test among the conditions under hypoxia. M1 tDCS resulted in no significant effect for any outcome measure.

CONCLUSIONS

We concluded that, as a novel finding, anodal stimulation of the left DLPFC might provide an ergogenic aid for endurance performance and cognitive function under the hypoxic condition probably via increasing neural drive to the working muscles, lowering RPE, and increasing perceptual responses.

Characterisation of Primary Human Hippocampal Astrocyte Cell Culture Following Exposure to Hypoxia

Background

The present study aimed to understand the characterisation of human hippocampal astrocyte following hypoxia exposure. Based on the preliminary screening, 15 min was chosen as the time point and the cells were exposed to different oxygen percentages.

Methods

The Trypan blue viability assay used to examine cell death. Immunofluorescence assay, glial fibrillary acidic protein (GFAP) was used to portray the morphology of astrocytes. The hypoxia-inducible factor 1 (HIF-1) staining was performed to confirm hypoxia induced cell death and there was a dramatic expression of HIF-1α displayed in exposed astrocyte cells compared to the control. In molecular level, genes were chosen, such as glyceraldehyde 3-phosphate dehydrogenase (GAPDH), GFAP, HIF-1α and B-cell lymphoma 2 (Bcl-2) and ran the reverse transcription-polymerase chain reaction (RT-PCR).

Results

Microscope revealed a filamentous and clear nucleus appearance in a control whereas the rupture nuclei with no rigid structure of the cell were found in the 3% oxygen. The control and hypoxia cells were also stained with the annexin V-fluorescein isothiocyanate (annexin V-FITC). Fluorescence microscope reveals astrocyte cells after hypoxia showed higher expression of nuclei but not in control. Merging PI and FITC showed the differences of nuclei expression between the control and hypoxia. In the molecular analysis, there were significant changes of GFAP, HIF-1α and Bcl-2 in hypoxia exposed cells when compared to the control group.

Conclusion

Cells that were exposed to hypoxia (3% oxygen for 15 min) clearly showed damage. General view of human hippocampal astrocyte genomic response to hypoxia was obtained.

The effects of acute high-intensity aerobic exercise on cognitive performance: A structured narrative review

It is well established that acute moderate-intensity exercise improves cognitive performance. However, the effects of acute high-intensity aerobic exercise on cognitive performance have not been well characterized. In this review, we summarize the literature investigating the exercise-cognition interaction, especially focusing on high-intensity aerobic exercise. We discuss methodological and physiological factors that potentially mediate cognitive performance in response to high-intensity exercise. We propose that the effects of high-intensity exercise on cognitive performance are primarily affected by the timing of cognitive task (during vs. after exercise, and the time delay after exercise). In particular, cognitive performance is more likely to be impaired during high-intensity exercise when both cognitive and physiological demands are high and completed simultaneously (i.e., the dual-task paradigm). The effects may also be affected by the type of cognitive task, physical fitness, exercise mode/duration, and age. Second, we suggest that interactions between changes in regional cerebral blood flow (CBF), cerebral oxygenation, cerebral metabolism, neuromodulation by neurotransmitters/neurotrophic factors, and a variety of psychological factors are promising candidates that determine cognitive performance in response to acute high-intensity exercise. The present review has implications for recreational, sporting, and occupational activities where high cognitive and physiological demands are required to be completed concurrently.

Sprint Interval Exercise Improves Cognitive Performance Unrelated to Postprandial Glucose Fluctuations at Different Levels of Normobaric Hypoxia

Objective: The aim of our study was to examine cognition response to sprint interval exercise (SIE) against different levels of hypoxia. Research design and methods: 26 recreational active males performed SIE (20 × 6 s of all-out cycling bouts, 15 s of passive recovery) under normoxia (FIO2: 0.209), moderate hypoxia (FIO2: 0.154), and severe hypoxia (FIO2: 0.112) in a single-blinded crossover design. Cognitive function and blood glucose were assessed before and after 0, 10, 30, and 60 min of the SIE. Heart rate (HR), peripheral oxygen saturation (SpO2), and ratings of perceived exertion (RPE, the Borg 6−20-point scale) during each SIE trial were recorded before and immediately after every five cycling bouts, and after 0, 10, 30, and 60 min of the SIE. Results: All the three SIE trials had a significantly faster overall reaction time in the Stroop test at 10 min after exercise as compared to that of the baseline value (p = 0.003, ƞ2 = 0.606), and returned to normal after 60 min. The congruent RT at 10 min after SIE was significantly shorter than that of the baseline (p < 0.05, ƞ2 = 0.633), while the incongruent RT at both 10 min and 30 min were significantly shorter than that measured at baseline (p < 0.05, ƞ2 = 0.633). No significant differences in terms of accuracy were found across the three trials at any time points (p = 0.446, ƞ2 = 0.415). Blood glucose was significantly reduced at 10 min and was sustained for at least 60 min after SIE when compared to pre-exercise in all trials (p < 0.05). Conclusions: Acute SIE improved cognitive function regardless of oxygen conditions, and the sustained improvement following SIE could last for at least 10−30 min and was unaffected by the altered blood glucose level.

Intensity-dependent acute aerobic exercise: Effect on reactive control of attentional functions in acclimatized lowlanders at high altitude

Human attentional function is sensitive to hypoxia. However, little is known about whether and how attentional function is altered after acute aerobic exercise at high altitude, especially for acclimatized lowlanders. In this study, we used the Attention Network Test (ANT) to measure alerting, orienting, and executive control functions and the Stroop Color and Word Test (SCWT) with a different proportion of incongruent trials to investigate proactive and reactive control of executive function. We randomly divided the sample of 160 Tibetan lowlanders who had lived in the highlands for more than two years into four groups. Each of three groups performed 20 min of low-, moderate-, or high-intensity acute aerobic exercise, separately, and a control group watched a 20-min documentary. The ANT and SCWT were conducted before and after exercise or watching the documentary. The results indicated that the executive control effects of the three experimental groups significantly decreased and, in the posttest, the executive control effects of the high-intensity group were lower than those of the low-intensity group. Furthermore, the accuracy of the moderate- and high-intensity groups was increased significantly in the blocks containing 25% incongruent trials of SCWT task. These results suggest that the acute aerobic exercise at high altitude will improve the reactive control of attentional functions in acclimatized lowlanders, and the intensity may play an important role in the exercise-cognition interaction at high altitude.

The Impact of Sprint Interval Exercise in Acute Severe Hypoxia on Executive Function

Kong, Zhaowei, Qian Yu, Shengyan Sun, On Kei Lei, Yu Tian, Qingde Shi, Jinlei Nie, and Martin Burtscher. The impact of sprint interval exercise in acute severe hypoxia on executive function. High Alt Med Biol. 23: 135-145, 2022. Objective: The present study evaluated executive performance responses to sprint interval exercise in normoxia and relatively severe hypoxia. Methods: Twenty-five physically active men (age 22 ± 2 years; maximal oxygen uptake 43 ± 2 ml/[kg·min]) performed four trials including two normoxic (F_IO₂ = 0.209) and two normobaric hypoxic trials (F_IO₂ = 0.112), at rest (control) and exercise at the same time on different days. The exercise scheme consisted of 20 sets of 6-seconds all-out cycling sprint interspersed with 15-seconds recovery. The Stroop task was conducted before, 10, 30, and 60 minutes after each trial, whereas peripheral oxygen saturation (SpO₂), heart rate, ratings of perceived exertion, and feelings of arousal were additionally recorded immediately after the interventions. Results: Despite the low SpO₂ levels, both resting and sprint interval exercise in hypoxia had no adverse effects on executive function. Exercise elicited executive improvements in normoxia (-5.3% and -3.4% at 10 and 30 minutes after exercise) and in hypoxia (-7.8% and -4.3%), which is reflected by ameliorating incongruent reaction time and its 30-minutes sustained effects (p = 0.018). Conclusions: The findings demonstrate that sprint interval exercise caused sustained executive benefits, and exercise in relatively severe hypoxia did not impair executive performance.

Cognitive Improvement After Aerobic and Resistance Exercise Is Not Associated With Peripheral Biomarkers

The role of peripheral biomarkers following acute physical exercise on cognitive improvement has not been systematically evaluated. This study aimed to explore the role of peripheral circulating biomarkers in executive performance following acute aerobic and resistance exercise. Nineteen healthy males completed a central executive (Go/No-Go) task before and after 30-min of perceived intensity matched aerobic and resistance exercise. In the aerobic condition, the participants cycled an ergometer at 40% peak oxygen uptake. In the resistance condition, they performed resistance exercise using elastic bands. Before and after an acute bout of physical exercise, venous samples were collected for the assessment of following biomarkers: adrenaline, noradrenaline, glucose, lactate, cortisol, insulin-like growth hormone factor 1, and brain-derived neurotrophic factor. Reaction time decreased following both aerobic exercise and resistance exercise (p = 0.04). Repeated measures correlation analysis indicated that changes in reaction time were not associated with the peripheral biomarkers (all p &gt; 0.05). Accuracy tended to decrease in the resistance exercise condition (p = 0.054). Accuracy was associated with changes in adrenaline [rrm(18) = −0.51, p = 0.023], noradrenaline [rrm(18) = −0.66, p = 0.002], lactate [rrm(18) = −0.47, p = 0.035], and brain-derived neurotrophic factor [rrm(17) = −0.47, p = 0.044] in the resistance condition. These findings suggest that these peripheral biomarkers do not directly contribute to reduction in reaction time following aerobic or resistance exercise. However, greater sympathoexcitation, reflected by greater increase in noradrenaline, may be associated with a tendency for a reduction in accuracy after acute resistance exercise.

Effects of Cardiorespiratory Fitness on Cerebral Oxygenation in Healthy Adults: A Systematic Review

Introduction

Exercise is known to improve cognitive functioning and the cardiorespiratory hypothesis suggests that this is due to the relationship between cardiorespiratory fitness (CRF) level and cerebral oxygenation. The purpose of this systematic review is to consolidate findings from functional near-infrared spectroscopy (fNIRS) studies that examined the effect of CRF level on cerebral oxygenation during exercise and cognitive tasks.

Methods

Medline, Embase, SPORTDiscus, and Web of Science were systematically searched. Studies categorizing CRF level using direct or estimated measures of V̇O_2max and studies measuring cerebral oxygenation using oxyhemoglobin ([HbO₂]) and deoxyhemoglobin ([HHb]) were included. Healthy young, middle-aged, and older adults were included whereas patient populations and people with neurological disorders were excluded.

Results

Following PRISMA guidelines, 14 studies were retained following abstract and full-text screening. Cycle ergometer or treadmill tests were used as direct measures of CRF, and one study provided an estimated value using a questionnaire. Seven studies examined the effects of CRF on cerebral oxygenation during exercise and the remaining seven evaluated it during cognitive tasks. Increased [HbO₂] in the prefrontal cortex (PFC) was observed during cognitive tasks in higher compared to lower fit individuals. Only one study demonstrated increased [HHb] in the higher fit group. Exercise at submaximal intensities revealed increased [HbO₂] in the PFC in higher compared to lower fit groups. Greater PFC [HHb] was also observed in long- vs. short-term trained males but not in females. Primary motor cortex (M1) activation did not differ between groups during a static handgrip test but [HHb] increased beyond maximal intensity in a lower compared to higher fit group.

Conclusion

Consistent with the cardiorespiratory hypothesis, higher fit young, middle-aged, and older adults demonstrated increased cerebral oxygenation compared to lower fit groups. Future research should implement randomized controlled trials to evaluate the effectiveness of interventions that improve CRF and cerebral oxygenation longitudinally.

The Acute Effects of Normobaric Hypoxia on Strength, Muscular Endurance and Cognitive Function: Influence of Dose and Sex

The aim of this study was to examine the acute effects of different levels of hypoxia on maximal strength, muscular endurance, and cognitive function in males and females. In total, 13 males (mean ± SD: age, 23.6 ± 2.8 years; height, 176.6 ± 3.9 cm; body mass, 76.6 ± 2.1 kg) and 13 females (mean ± SD: age, 22.8 ± 1.4 years; height, 166.4 ± 1.9 cm; body mass, 61.6 ± 3.4 kg) volunteered for a randomized, double-blind, crossover study. Participants completed a one repetition strength and muscular endurance test (60% of one repetition maximum to failure) for squat and bench press following four conditions; (i) normoxia (900 m altitude; FiO2: 21%); (ii) low dose hypoxia (2000 m altitude; FiO2: 16%); (iii) moderate dose hypoxia (3000 m altitude; FiO2: 14%); and (iv) high dose hypoxia (4000 m altitude; FiO2: 12%). Heart rate, blood lactate, rating of perceived exertion, and cognitive function was also determined during each condition. The one repetition maximum squat (p = 0.33) and bench press (p = 0.68) did not differ between conditions or sexes. Furthermore, squat endurance did not differ between conditions (p = 0.34). There was a significant decrease in bench press endurance following moderate (p = 0.02; p = 0.04) and high (p = 0.01; p = 0.01) doses of hypoxia in both males and females compared to normoxia and low dose hypoxia, respectively. Cognitive function, ratings of perceived exertion, and lactate were also significantly different in high and moderate dose hypoxia conditions compared to normoxia (p < 0.05). Heart rate was not different between the conditions (p = 0.30). In conclusion, high and moderate doses of acute normobaric hypoxia decrease upper body muscular endurance and cognitive performance regardless of sex; however, lower body muscular endurance and maximal strength are not altered.

Effect of a speed ascent to the top of Europe on cognitive function in elite climbers

PURPOSE

The combined effects of acute hypoxia and exercise on cognition remain to be clarified. We investigated the effect of speed climbing to high altitude on reactivity and inhibitory control in elite climbers.

METHODS

Eleven elite climbers performed a speed ascent of the Mont-Blanc (4810 m) and were evaluated pre- (at 1000 m) and immediately post-ascent (at 3835 m). In both conditions, a Simon task was done at rest (single-task session, ST) and during a low-intensity exercise (dual-task session, DT). Prefrontal cortex (PFC) oxygenation and middle cerebral artery velocity (MCAv) were monitored using near-infrared spectroscopy and transcranial Doppler, respectively, during the cognitive task. Self-perceived mental fatigue and difficulty to perform the cognitive tests were estimated using a visual analog scale. Heart rate and pulse oxygenation (SpO₂) were monitored during the speed ascent.

RESULTS

Elite climbers performed an intense (~ 50% of the time ≥ 80% of maximal heart rate) and prolonged (8h58 ± 6 min) exercise in hypoxia (minimal SpO₂ at 4810 m: 78 ± 4%). Reaction time and accuracy during the Simon task were similar pre- and post-ascent (374 ± 28 ms vs. 385 ± 39 ms and 6 ± 4% vs. 5 ± 4%, respectively; p > 0.05), despite a reported higher mental fatigue and difficulty to perform the Simon task post-ascent (all p < 0.05). The magnitude of the Simon effect was unaltered (p > 0.05), suggesting a preserved cognitive control post-ascent. Pattern of PFC oxygenation and MCAv differed between pre- and post-ascent as well as between ST and DT conditions.

CONCLUSIONS

Cognitive control is not altered in elite climbers after a speed ascent to high-altitude despite substantial cerebral deoxygenation and fatigue perception.

A Review of Cognitive Changes During Acute Aerobic Exercise

A growing body of work has investigated the effects of acute, or single bouts of, aerobic exercise on cognitive function. However, review of this research has largely focused on changes following exercise, with less focus on cognitive changes during exercise. The purpose of this review is to discuss the critical characteristics of this literature to date, including: (1) what has been done, (2) what has been found, and (3) what is next. Furthermore, previous meta-analytic reviews have demonstrated there is a small positive effect on cognition when measured during exercise, with executive functions showing the largest effects. However, these reviews group executive functions together. Here we explore how inhibition, working memory and cognitive flexibility are individually impacted by factors such as exercise intensity or duration. Searches of electronic databases and reference lists from relevant studies resulted in 73 studies meeting inclusion criteria. Studies were grouped by executive and non-executive cognitive domains, intensity and duration of exercise bouts. Within the executive domain, we found that effects on working memory and cognitive flexibility remain mixed, effects on inhibition are clearer. Moderate intensity exercise improves response time, vigorous intensity impairs accuracy. Moderate to vigorous intensity improves response time across non-executive domains of attention, motor speed and information processing, with no significant effects on accuracy. Memory processes are consistently improved during exercise. Effects of exercise duration on response time and accuracy are nuanced and vary by cognitive domain. Studies typically explore durations of 45 min or less, extended exercise durations remain largely unexplored. We highlight factors to consider when assessing exercise-cognition relationships, as well as current gaps and future directions for work in this field.

Effect of Exercise on Brain Health: The Potential Role of Lactate as a Myokine

It has been well established in epidemiological studies and randomized controlled trials that habitual exercise is beneficial for brain health, such as cognition and mental health. Generally, it may be reasonable to say that the physiological benefits of acute exercise can prevent brain disorders in late life if such exercise is habitually/chronically conducted. However, the mechanisms of improvement in brain function via chronic exercise remain incompletely understood because such mechanisms are assumed to be multifactorial, such as the adaptation of repeated acute exercise. This review postulates that cerebral metabolism may be an important physiological factor that determines brain function. Among metabolites, the provision of lactate to meet elevated neural activity and regulate the cerebrovascular system and redox states in response to exercise may be responsible for exercise-enhanced brain health. Here, we summarize the current knowledge regarding the influence of exercise on brain health, particularly cognitive performance, with the underlying mechanisms by means of lactate. Regarding the influence of chronic exercise on brain function, the relevance of exercise intensity and modality, particularly high-intensity interval exercise, is acknowledged to induce “metabolic myokine” (i.e., lactate) for brain health.

Hypoxic and Hyperoxic Breathing as a Complement to Low-Intensity Physical Exercise Programs: A Proof-of-Principle Study

Inflammation is an adaptive response to both external and internal stimuli including infection, trauma, surgery, ischemia-reperfusion, or malignancy. A number of studies indicate that physical activity is an effective means of reducing acute systemic and low-level inflammation occurring in different pathological conditions and in the recovery phase after disease. As a proof-of-principle, we hypothesized that low-intensity workout performed under modified oxygen supply would elicit a "metabolic exercise" inducing a hormetic response, increasing the metabolic load and oxidative stress with the same overall effect expected after a higher intensity or charge exercise. Herein, we report the effect of a 5-week low-intensity, non-training, exercise program in a group of young healthy subjects in combination with the exposure to hyperoxia (30% and 100% pO₂, respectively) or light hypoxia (15% pO₂) during workout sessions on several inflammation and oxidative stress parameters, namely hemoglobin (Hb), redox state, nitric oxide metabolite (NOx), inducible nitric oxide synthase (iNOS), inflammatory cytokine expression (TNF-α, interleukin (IL)-6, IL-10), and renal functional biomarkers (creatinine, neopterin, and urates). We confirmed our previous reports demonstrating that intermittent hyperoxia induces the normobaric oxygen paradox (NOP), a response overlapping the exposure to hypoxia. Our data also suggest that the administration of modified air composition is an expedient complement to a light physical exercise program to achieve a significant modulation of inflammatory and immune parameters, including cytokines expression, iNOS activity, and oxidative stress parameters. This strategy can be of pivotal interest in all those conditions characterized by the inability to achieve a sufficient workload intensity, such as severe cardiovascular alterations and articular injuries failing to effectively gain a significant improvement of physical capacity.

Does exercise have a protective effect on cognitive function under hypoxia? A systematic review with meta-analysis

OBJECTIVE

This study aimed to examine (1) the independent effects of hypoxia on cognitive function and (2) the effects of exercise on cognition while under hypoxia.

METHODS

Design: Systematic review with meta-analysis.

DATA SOURCES

PubMed, Scopus, Web of Science, PsychInfo, and SPORTDiscus were searched. Eligibility criteria for selecting studies: randomized controlled trials and nonrandomized controlled studies that investigated the effects of chronic or acute exercise on cognition under hypoxia were considered (Aim 2), as were studies investigating the effects of hypoxia on cognition (Aim 1).

RESULTS

In total, 18 studies met our inclusionary criteria for the systematic review, and 12 studies were meta-analyzed. Exposure to hypoxia impaired attentional ability (standardized mean difference (SMD) = -0.4), executive function (SMD = -0.18), and memory function (SMD = -0.26), but not information processing (SMD = 0.27). Aggregated results indicated that performing exercise under a hypoxia setting had a significant effect on cognitive improvement (SMD = 0.3, 95% confidence interval: 0.14 - 0.45, I² = 54%, p < 0.001). Various characteristics (e.g., age, cognitive task type, exercise type, exercise intensity, training type, and hypoxia level) moderated the effects of hypoxia and exercise on cognitive function.

CONCLUSION

Exercise during exposure to hypoxia improves cognitive function. This association appears to be moderated by individual and exercise/hypoxia-related characteristics.

The exercise intensity of square-stepping exercise in community-dwelling late elderly females

[Purpose] Square-stepping exercise is recommended for elderly people, as it has a positive effect on cognitive and physical functions; however, few studies have examined the exercise intensity of square-stepping exercise. Therefore, we aimed to examine the exercise intensity of square-stepping exercise in community-dwelling late elderly females. [Participants and Methods] Study 1: The participants, constituting 12 community-dwelling late elderly females (age: 78.7 ± 3.8 years), performed the three target step patterns. Exhaled gas, heart rate, and rating of perceived exertion using the Borg Scale were measured during square-stepping exercise. Study 2: Participants were 57 community-dwelling elderly females (81.2 ± 4.3 years old). The exercise intensity, heart rate, and rating of perceived exertion using the Borg Scale during square-stepping exercise were measured. [Results] Study 1: The average METs of the 3 target step patterns was 3.6 ± 0.7, and the %heart rate reserve and rating of perceived exertion were 54.3 ± 20.0% and 11.4 ± 1.9%, respectively. Study 2: The average METs during the square-stepping exercise program was 2.1 ± 0.2, and the %heart rate reserve and rating of perceived exertion were 19.6 ± 10.2% and 11.3 ± 1.4%, respectively. [Conclusion] Square-stepping exercise was confirmed to be a low to moderate intensity exercise program and is expected to improve health and physical fitness.

Cognitive Impairment during High-Intensity Exercise: Influence of Cerebral Blood Flow

PURPOSE

Cognitive performance appears to be impaired during high-intensity exercise, and this occurs concurrently with a reduction in cerebral blood flow (CBF). However, it is unclear whether cognitive impairment during high-intensity exercise is associated with reduced CBF. We tested the hypothesis that a reduction in CBF is responsible for impaired cognitive performance during high-intensity exercise.

METHODS

Using a randomized crossover design 17 healthy males performed spatial delayed response and Go/No-Go tasks in three conditions (exercise [EX], exercise+CO2 [EX+CO2], and a nonexercising control [CON]). In the EX and EX+CO2, they performed cognitive tasks at rest and during 8 min of moderate and high-intensity exercise. Exercise intensity corresponded to ~50% (moderate) and ~80% (high) of peak oxygen uptake. In the EX+CO2, the participants inspired hypercapnic gas (2% CO2) during high-intensity exercise. In the CON, they performed the cognitive tasks without exercise.

RESULTS

Middle cerebral artery mean velocity increased during high-intensity exercise in the EX+CO2 relative to the EX (69.4 [10.6] cm·s, vs 57.2 [7.7] cm·s, P < 0.001). Accuracy of the cognitive tasks was impaired during high-intensity exercise in the EX (84.1% [13.3%], P < 0.05) and the EX+ CO2 (85.7 [11.6%], P < 0.05) relative to rest (EX: 95.1% [5.3%], EX+CO2: 95.1 [5.3%]). However, no differences between the EX and the EX+CO2 were observed (P > 0.10). These results demonstrate that restored CBF did not prevent cognitive impairment during high-intensity exercise.

CONCLUSIONS

We conclude that a reduction in CBF is not responsible for impaired cognitive performance during high-intensity exercise.

Application of carbon dioxide to the skin and muscle oxygenation of human lower-limb muscle sites during cold water immersion

Background

Cold therapy has the disadvantage of inducing vasoconstriction in arterial and venous capillaries. The effects of carbon dioxide (CO₂) hot water depend mainly on not only cutaneous vasodilation but also muscle vasodilation. We examined the effects of artificial CO₂ cold water immersion (CCWI) on skin oxygenation and muscle oxygenation and the immersed skin temperature.

Subjects and Methods

Fifteen healthy young males participated. CO₂-rich water containing CO₂ >1,150 ppm was prepared using a micro-bubble device. Each subject’s single leg was immersed up to the knee in the CO₂-rich water (20 °C) for 15 min, followed by a 20-min recovery period. As a control study, a leg of the subject was immersed in cold tap-water at 20 °C (CWI). The skin temperature at the lower leg under water immersion (T_sk-WI) and the subject’s thermal sensation at the immersed and non-immersed lower legs were measured throughout the experiment. We simultaneously measured the relative changes of local muscle oxygenation/deoxygenation compared to the basal values (Δoxy[Hb+Mb], Δdeoxy[Hb+Mb], and Δtotal[Hb+Mb]) at rest, which reflected the blood flow in the muscle, and we measured the tissue O₂ saturation (S_tO₂) by near-infrared spectroscopy on two regions of the tibialis anterior (TA) and gastrocnemius (GAS) muscles.

Results

Compared to the CWI results, the Δoxy[Hb+Mb] and Δtotal[Hb+Mb] in the TA muscle at CCWI were increased and continued at a steady state during the recovery period. In GAS muscle, the Δtotal[Hb+Mb] and Δdeoxy[Hb+Mb] were increased during CCWI compared to CWI. Notably, S_tO₂values in both TA and GAS muscles were significantly increased during CCWI compared to CWI. In addition, compared to the CWI, a significant decrease in T_sk at the immersed leg after the CCWI was maintained until the end of the 20-min recovery, and the significant reduction continued.

Discussion

The combination of CO₂ and cold water can induce both more increased blood inflow into muscles and volume-related (total heme concentration) changes in deoxy[Hb+Mb] during the recovery period. The T_sk-WI stayed lower with the CCWI compared to the CWI, as it is associated with vasodilation by CO₂.

New Directions in Exercise Prescription: Is There a Role for Brain-Derived Parameters Obtained by Functional Near-Infrared Spectroscopy?

In the literature, it is well established that regular physical exercise is a powerful strategy to promote brain health and to improve cognitive performance. However, exact knowledge about which exercise prescription would be optimal in the setting of exercise–cognition science is lacking. While there is a strong theoretical rationale for using indicators of internal load (e.g., heart rate) in exercise prescription, the most suitable parameters have yet to be determined. In this perspective article, we discuss the role of brain-derived parameters (e.g., brain activity) as valuable indicators of internal load which can be beneficial for individualizing the exercise prescription in exercise–cognition research. Therefore, we focus on the application of functional near-infrared spectroscopy (fNIRS), since this neuroimaging modality provides specific advantages, making it well suited for monitoring cortical hemodynamics as a proxy of brain activity during physical exercise.

Acute aerobic exercise impairs aspects of cognitive function at high altitude

Hypoxia-mediated cognitive dysfunction can be transiently mitigated by exercise in a laboratory-based setting. Whether this effect holds true in the context of high altitude hypoxia has not been determined. We investigated the effect of acute aerobic exercise on cognitive function (CF) at low (1400m) and high altitude (4240m). Fifteen volunteers (24.1±3.5yrs; 9 females) exercised for 20-min at 40-60% of their heart rate reserve at low and high altitude. CF was assessed before and 10-min after exercise using a tablet-based battery of executive function tests. A sea-level control group (n=13; 24.2±2.4 years; 9 females) performed time-matched CF tests to assess the contribution of a learning effects due to repeated testing. Measures of resting CF were unaffected by ascent to high altitude. Following high altitude exercise, performance significantly worsened on the digit symbol substitution task - a test of processing speed, working memory, and visuospatial attention (z=0.01 vs. -0.59, p=0.02, η²=0.35). No effect was found on other measures of CF following exercise. There was no association between changes in peripheral oxygen saturation and changes in CF following high altitude exercise (r=0.22, p=0.44), but higher hemoglobin concentration at high altitude was associated with a decline in CF following exercise at high altitude (r=-0.65, p=0.02). Acute aerobic exercise performed at high altitude impairs some aspects of CF, whereas other CF tests remain unchanged. The strong ecological validity of this study warrants attention and follow-up investigations are needed to better characterize selective impairment of CF with high altitude exercise.

Relationship Between Cerebral Oxygenation and Skin Blood Flow at the Frontal Lobe during Progressive Hypoxia: Impact of Acute Hypotension

We investigated the relationship between cerebral oxygenation (COX) and skin blood flow (SkBF) at the left frontal lobes of 10 healthy young men during progressive hypoxia (∼ -1 h at each of 21%, 18%, 15%, and 12% of inspired oxygen [FiO₂]). Acute hypotension was manipulated by a thigh-cuff-release technique, where a pressure of 220 mmHg was applied at both thigh muscles for 3 min and the cuff was immediately released to induce acute hypotension. While the resting baseline for COX before the thigh-cuff release manipulation decreased gradually with the reduction of FiO₂ (P < 0.05), the resting baseline for SkBF, mean arterial blood pressure (MAP), and cutaneous vascular conductance (CVC) were unaffected by FiO₂ (P > 0.05). The acute hypotension that was induced by the thigh-cuff release decreased COX, SkBF, MAP, and CVC; thereafter, these values recovered toward their baseline values. During the hypotension phase, while the time to the nadir values for COX slowed progressively with reductions in FiO₂ (P < 0.05), those for SkBF, MAP, and CVC were unaffected by FiO₂ (P > 0.05). These results suggest that COX may not be associated with SkBF for the protocol or with the subjects in the present study.

Carbohydrate supplementation and psychophysiological responses during moderate exercise in hypoxia

Background

Rating of Perceived Exertion (RPE) is a subjective scale to monitor overload and fatigue during exercise. Hypoxia may worsen the perception of fatigue, compromising the self-reported perception of effort and increasing RPE. The objective was to evaluate the effects of carbohydrate (CHO) supplementation on RPE during exercise in hypoxia simulating 4200 m.

Methods

Eight male physically active volunteers performed two exercises at 50% VO_2peak and 1% slope: exercise in hypoxia + placebo or exercise in hypoxia + CHO (6% maltodextrin) with supplementation at 20, 40, and 60 min during exercise. Oxygen Saturation (SaO₂%) was assessed at baseline and after exercise, while RPE and HR were measured each 10 min during the trial.

Results

SaO₂% decreased after exercise in both conditions of hypoxia compared to rest. The RPE did not differ between groups. However, the RPE increased in hypoxia after 20 min of exercise in relation to 10 min. The Area Under the Curve (AUC) of RPE was lower in hypoxia + CHO compared to hypoxia. The AUC of the HR/RPE ratio in the hypoxia + CHO group was higher in relation to hypoxia.

Conclusions

Our results indicate that CHO supplementation does not change RPE induced by 60 min of exercise at 50% VO_2peak in hypoxia equivalent to 4200 m at the different times analyzed. However, in hypoxia + CHO the (AUC)-60 min of total RPE decreased during exercise, while the heart rate/RPE ratio improved, indicating lower RPE in the hypoxic environment.

The Impact of Environmental Stress on Cognitive Performance: A Systematic Review

OBJECTIVE

In this review, we detail the impact of environmental stress on cognitive and military task performance and highlight any individual characteristics or interventions which may mitigate any negative effect.

BACKGROUND

Military personnel are often deployed in regions markedly different from their own, experiencing hot days, cold nights, and trips both above and below sea level. In spite of these stressors, high-level cognitive and operational performance must be maintained.

METHOD

A systematic review of the electronic databases Medline (PubMed), EMBASE (Scopus), PsycINFO, and Web of Science was conducted from inception up to September 2018. Eligibility criteria included a healthy human cohort, an outcome of cognition or military task performance and assessment of an environmental condition.

RESULTS

The search returned 113,850 records, of which 124 were included in the systematic review. Thirty-one studies examined the impact of heat stress on cognition; 20 of cold stress; 59 of altitude exposure; and 18 of being below sea level.

CONCLUSION

The severity and duration of exposure to the environmental stressor affects the degree to which cognitive performance can be impaired, as does the complexity of the cognitive task and the skill or familiarity of the individual performing the task.

APPLICATION

Strategies to improve cognitive performance in extreme environmental conditions should focus on reducing the magnitude of the physiological and perceptual disturbance caused by the stressor. Strategies may include acclimatization and habituation, being well skilled on the task, and reducing sensations of thermal stress with approaches such as head and neck cooling.

The interactive effects of acute exercise and hypoxia on cognitive performance: A narrative review

Acute moderate intensity exercise has been shown to improve cognitive performance. In contrast, hypoxia is believed to impair cognitive performance. The detrimental effects of hypoxia on cognitive performance are primarily dependent on the severity and duration of exposure. In this review, we describe how acute exercise under hypoxia alters cognitive performance, and propose that the combined effects of acute exercise and hypoxia on cognitive performance are mainly determined by interaction among exercise intensity and duration, the severity of hypoxia, and duration of exposure to hypoxia. We discuss the physiological mechanism(s) of the interaction and suggest that alterations in neurotransmitter function, cerebral blood flow, and possibly cerebral metabolism are the primary candidates that determine cognitive performance when acute exercise is combined with hypoxia. Furthermore, acclimatization appears to counteract impaired cognitive performance during prolonged exposure to hypoxia although the precise physiological mechanism(s) responsible for this amelioration remain to be elucidated. This review has implications for sporting, occupational, and recreational activities at terrestrial high altitude where cognitive performance is essential. Further studies are required to understand physiological mechanisms that determine cognitive performance when acute exercise is performed in hypoxia.

Salivary Metabolome and Soccer Match: Challenges for Understanding Exercise induced Changes

Saliva samples of seventeen soccer players were analyzed by nuclear magnetic resonance before and after an official match. Two different ways of normalizing data are discussed, using total proteins and total metabolite concentrations. Changes in markers related to energy, hydration status, amino acids and other compounds were found. The limits and advantages of using saliva to define the systemic responses to exercise are examined, both in terms of data normalization and interpretation, and the time that the effect lasts in this biofluid, which is shorter to that commonly observed in blood. The heterogeneous nature and different timing of the exercise developed by players also plays an important role in the metabolic changes that can be measured. Our work focuses mainly on three different aspects: The effect that time sampling has on the observed effect, the type of normalization that is necessary to perform in order to cope with changes in water content, and the metabolic response that can be observed using saliva.

Repeated Treadmill Sprints Impair Cognitive Performance in Amateur Team-Sport Athletes When Performed in Normobaric Hypoxia

This study determined if a single bout of repeated-sprint running under hypoxic (RSH) conditions was associated with impaired cognitive function when compared with repeated-sprint running under normoxic (RSN) conditions. Eleven amateur team-sport athletes performed a repeated-sprint running protocol (4 sets of 4, 4-s all-out sprints; i.e., RSR₄₄₄) under both conditions (14.5% and 20.9% O₂) on a non-motorized treadmill. Changes in S_pO₂, pre-frontal cortex total haemoglobin (Δ[THb]), oxyhaemoglobin (Δ[O₂Hb]), deoxyhaemoglobin (Δ[HHb]) and cognitive function (detection task: DET; identification task: IDN; one card learning task: OCL; performed pre and 20 min post RSR₄₄₄) were examined. During RSH, S_pO₂ was lower following each set (p ≤ 0.05), while [HHb] was higher after each set (p ≤ 0.05) compared with RSN. In addition, while there was no effect of condition on DET (p = 0.20) or IDN (p = 0.14), OCL accuracy was lower after, compared with before, RSH (p=0.04), but not RSN (p = 0.52). A significant relationship was observed between Δ[HHB] and ΔOCL accuracy (r = -0.68, p = 0.01). Performance of a single bout of RSH with 14.5% O₂ resulted in impaired cognitive function in amateur team-sport athletes. Coaches should be mindful of timing of RSH prescription with regard to other training sessions that challenge speed and movement accuracy.

Effects of periodic carbohydrate ingestion on endurance and cognitive performances during a 40-km cycling time-trial under normobaric hypoxia in well-trained triathletes

The purpose of this study was to examine CHO ingestion on a cognitive task using a field-simulated time-trial (TT) under hypoxia in well-trained triathletes. Ten male triathletes (age: 22.1 ± 1.1 years; VO₂max: 59.4 ± 1.4 ml/kg/min) participated in this double-blind/crossover/counter-balanced design study. Participants completed 3 TT trials: 1) normoxic placebo (NPLA; FiO₂ = 20.9%), 2) hypoxic placebo (HPLA; FiO₂ = 16.3%), and 3) hypoxic CHO (HCHO; 6% CHO provided as 2 ml/kg/15 min; FiO₂ = 16.3%). During the TT, physiological responses (SpO₂, HR, RPE, and blood glucose/lactate), cognitive performance, and cerebral haemodynamics were measured. Hypoxia reduced TT performance by ~3.5-4% (p < 0.05), but CHO did not affect TT performance under hypoxia. For the cognitive task, CHO slightly preserved exercise-induced cognitive reaction speed but did not affect response accuracy during hypoxic exercise. However, CHO did not preserve the decreased Hb-Diff (cerebral blood flow, CBF) and increased HHb in the prefrontal lobe (p < 0.05) during hypoxic exercise, and CHO failed to preserve hypoxia-suppressed prefrontal CBF and tissue oxygen saturation. In conclusion, the present study demonstrates that CHO is effective in sustaining reaction speed for a cognitive task but not promoting TT performance during hypoxic exercise, which would be important for strategy-/decision-making when athletes compete at moderate high-altitude.

Severe Hypoxia Does Not Offset the Benefits of Exercise on Cognitive Function in Sedentary Young Women

Purpose: To examine the effect of acute moderate-intensity continuous exercise performed under normobaric severe hypoxia on cognition, compared to sea-level normoxia. Methods: Thirty healthy inactive women randomly performed two experimental trials separated by at least three days but at approximately the same time of day. Executive functions were measured during the follicular stage via an interference control task before (rest) and during exercise with 45% peak power output under normobaric normoxia (PIO₂ = 150 mmHg, FIO₂ = 0.21), and (2) hypoxia (PIO₂ = 87 mmHg, FIO₂ = 0.12, simulated at an altitude of 4000 m). Reaction time (RT), accuracy rate (AC), heart rate, ratings of perceived exertion, and peripheral oxygen saturation (SpO₂) were collected before and during exercise. Results: RT (p < 0.05, η²_p = 0.203) decreased during moderate exercise when compared at rest, while a short bout of severe hypoxia improved RT (p < 0.05, η²_p = 0.134). Exercise and hypoxia had no effects on AC (p > 0.05). No significant associations were found between the changes of RT and SpO₂ under the conditions of normoxia and hypoxia (p > 0.05). Conclusions: At the same phase of the menstrual cycle, a short bout of severe hypoxia simulated at 4000 m altitude caused no impairment at rest. RT during moderate exercise ameliorated in normoxia and severe hypoxia, suggesting that both exercise and short-term severe hypoxia have benefits on cognitive function in sedentary young women.

Combined effects of exposure to hypoxia and cool on walking economy and muscle oxygenation profiles at tibialis anterior

We investigated combined effects of ambient temperature (23°C or 13°C) and fraction of inspired oxygen (21%O₂ or 13%O₂) on energy cost of walking (C_w: J·kg^-1·km^-1) and economical speed (ES). Eighteen healthy young adults (11 males, seven females) walked at seven speeds from 0.67 to 1.67 m s^-1 (four min per stage). Environmental conditions were set; thermoneutral (N: 23°C) with normoxia (N: 21%O₂) = NN; 23°C (N) with hypoxia (H: 13%O₂) = NH; cool (C: 13°C) with 21%O₂ (N) = CN, and 13°C (C) with 13%O₂ (H) = CH. Muscle deoxygenation (HHb) and tissue O₂ saturation (StO₂) were measured at tibialis anterior. We found a significantly slower ES in NH (1.289 ± 0.091 m s^-1) and CH (1.275 ± 0.099 m s^-1) than in NN (1.334 ± 0.112 m s^-1) and CN (1.332 ± 0.104 m s^-1). Changes in HHb and StO₂ were related to the ES. These results suggested that the combined effects (exposure to hypoxia and cool) is nearly equal to exposure to hypoxia and cool individually. Specifically, acute moderate hypoxia slowed the ES by approx. 4%, but acute cool environment did not affect the ES. Further, HHb and StO₂ may partly account for an individual ES.

The Effects of High-Intensity Interval Exercise and Hypoxia on Cognition in Sedentary Young Adults

Background and Objectives: Limited research has evaluated the effects of acute exercise on cognition under different conditions of inspired oxygenation. Thus, the purpose of this study was to examine the effects of high-intensity interval exercise (HIE) under normoxia (inspired fraction of oxygen (FIO₂): 0.209) and moderate hypoxia (FIO₂: 0.154) on cognitive function. Design: A single-blinded cross-over design was used to observe the main effects of exercise and oxygen level, and interaction effects on cognitive task performance. Methods: Twenty inactive adults (10 males and 10 females, 19–27 years old) performed a cognitive task (i.e., the Go/No-Go task) before and immediately after an acute bout of HIE under normoxic and hypoxic conditions. The HIE comprised 10 repetitions of 6 s high-intensity cycling against 7.5% body weight interspersed with 30 s passive recovery. Heart rate, peripheral oxygen saturation (SpO₂) and rating of perceived exertion were monitored. Results: The acute bout of HIE did not affect the reaction time (p = 0.204, η² = 0.083) but the accuracy rate decreased significantly after HIE under both normoxic and hypoxic conditions (p = 0.001, η² = 0.467). Moreover, moderate hypoxia had no influence either on reaction time (p = 0.782, η² = 0.004) or response accuracy (p = 0.972, η² < 0.001). Conclusions: These results indicate that an acute session of HIE may impair response accuracy immediately post-HIE, without sacrificing reaction time. Meanwhile moderate hypoxia was found to have no adverse effect on cognitive function in inactive young adults, at least in the present study.

The influence of hypoxia and prolonged exercise on attentional performance at high and extreme altitudes: A pilot study

Introduction

Exposure to hypoxic conditions is reported to impair cognitive performance. Further, moderate physical exercise improves cognitive function, but little is known about the influence of exercise on cognitive function in hypoxia. Therefore, the current study aimed to examine the influence of hypoxia (HYP) and prolonged exercise (EX) on attentional performance.

Methods

A total of 80 participants (female: n = 29; male: n = 51) were assigned to four groups: HYP + EX (n = 15), HYP (n = 25), EX (n = 21) and normoxia (NOR) (n = 21). The Frankfurt Attention Inventory—2 (FAIR-2) was performed at four testing points (day 1, 14, 16 and 18) to assess attentional performance. All groups completed a pretest (D1) and a follow-up test (D18). In HYP + EX conditions, the cognitive task was performed in a hypoxic state after prolonged exercise (D14: 3950 m, D16: 5739 m) during a mountain climb on Mt. Kilimanjaro. Participants in HYP were tested under intermittent hypoxia at rest in a hypoxic chamber (D14: 3500 m, D16: 5800 m), and those in EX were tested under normoxia after prolonged exercise during a 7-day backcountry ski hiking tour. NOR was a control group, and participants completed all tests under normoxia and at rest.

Results

Hypoxia impaired the attentional functions performance value (PV) and continuity value (CV) for the HYP + EX (p = 0.000) and HYP (L: p = 0.025; K: p = 0.043) groups at 5739 m and 5800 m, respectively, but not the function quality value (QV). In contrast, the EX group did not exhibit changes in attentional function.

Conclusion

The current results suggest that attentional performance is impaired during extreme normobaric and hypobaric hypoxic exposure. We further conclude that greater cognitive impairment under hypobaric hypoxia during a mountain climb compared with normobaric hypoxia at rest is not caused by prolonged exercise, but may be influenced by other factors (e.g. low temperatures, dehydration, or sleep deprivation) that remain to be verified.

Acute cocoa flavanols intake improves cerebral hemodynamics while maintaining brain activity and cognitive performance in moderate hypoxia

INTRODUCTION

Acute cocoa flavanols (CF) intake has been suggested to modulate cognitive function and neurovascular coupling (NVC). Whether increased NVC is solely driven by improved vascular responsiveness or also by neuronal activity remains unknown. This study investigated the effects of acute CF intake on cognitive performance, NVC, and neuronal activity in healthy subjects in normoxia and hypoxia (4000 m simulated altitude; 12.7% O₂).

METHODS

Twenty healthy subjects (age 23.2 ± 4.3 years) performed four trials. Participants performed a Stroop task and "cognition" battery 2 h after acute CF (530 mg CF, 100 mg epicatechin) or placebo intake, and 30 min after initial exposure to hypoxia or normoxia. Electroencephalogram and functional near-infrared spectroscopy were used to analyze hemodynamic changes and neuronal activity.

RESULTS

CF enhanced NVC in the right prefrontal cortex during several tasks (risk decision making, visual tracking, complex scanning, spatial orientation), while neuronal activity was not affected. CF improved abstract thinking in normoxia, but not in hypoxia and did not improve other cognitive performances. Hypoxia decreased accuracy on the Stroop task, but performance on other cognitive tasks was preserved. NVC and neuronal activity during cognitive tasks were similar in hypoxia vs. normoxia, with the exception of increased β activity in the primary motor cortex during abstract thinking.

CONCLUSIONS

Acute CF intake improved NVC, but did not affect neuronal activity and cognitive performance in both normoxia and hypoxia. Most cognitive functions, as well as NVC and neuronal activity, did not decline by acute exposure to moderate hypoxia in healthy subjects.

The effects of multi-stage exercise with and without concurrent cognitive performance on cardiorespiratory and cerebral haemodynamic responses

INTRODUCTION

Studies of cerebral haemodynamics have shown changes with increased exercise intensity, but the patterns have been highly variable and reliable associations with cognitive performance have not been identified. The aim of this study was to examine whether exercise-induced changes in oxygenated haemoglobin (O₂Hb) led to changes in concomitant cognitive performance.

METHODS

This study examined cardiorespiratory and cerebral haemodynamics during multi-stage exercise from rest to exhaustion, with (Ex + C) and without (Ex) concurrent cognitive performance (Go/No-go task).

RESULTS

The presence of the cognitive task affected both cardiorespiratory and cerebral haemodynamics. The patterns in the cerebral haemodynamics during Ex and Ex + C diverged above the respiratory compensation threshold (RCT), but differences were significant only at 100% [Formula: see text], displaying increased deoxygenated haemoglobin (HHb), decreased difference between oxygenated and deoxygenated haemoglobin (HbDiff), and decreased cerebral oxygenation (COx) during Ex + C. More complex haemodynamic trends against intensity during Ex + C suggested that the presence of a cognitive task increases cerebral metabolic demand at high exercise intensities. The levels of O₂Hb, HHb, HbDiff and total haemoglobin increased most steeply at intensities around the RCT during both Ex and Ex + C, but these changes were not accompanied by improved cognitive performance.

CONCLUSION

The primary hypothesis, that cognitive performance would match changes in O₂Hb, was not supported. Small variations in reaction time and response accuracy across exercise intensities were not significant, suggesting that cognitive performance is unaffected by intense short-duration exercise. Our results add further evidence that exercise-induced changes in cerebral haemodynamics do not affect cognitive performance.

Cognitive function during exercise under severe hypoxia

Acute exercise has been demonstrated to improve cognitive function. In contrast, severe hypoxia can impair cognitive function. Hence, cognitive function during exercise under severe hypoxia may be determined by the balance between the beneficial effects of exercise and the detrimental effects of severe hypoxia. However, the physiological factors that determine cognitive function during exercise under hypoxia remain unclear. Here, we examined the combined effects of acute exercise and severe hypoxia on cognitive function and identified physiological factors that determine cognitive function during exercise under severe hypoxia. The participants completed cognitive tasks at rest and during moderate exercise under either normoxic or severe hypoxic conditions. Peripheral oxygen saturation, cerebral oxygenation, and middle cerebral artery velocity were continuously monitored. Cerebral oxygen delivery was calculated as the product of estimated arterial oxygen content and cerebral blood flow. On average, cognitive performance improved during exercise under both normoxia and hypoxia, without sacrificing accuracy. However, under hypoxia, cognitive improvements were attenuated for individuals exhibiting a greater decrease in peripheral oxygen saturation. Cognitive performance was not associated with other physiological parameters. Taken together, the present results suggest that arterial desaturation attenuates cognitive improvements during exercise under hypoxia.

Executive function after exhaustive exercise

PURPOSE

Findings concerning the effects of exhaustive exercise on cognitive function are somewhat equivocal. The purpose of this study was to identify physiological factors that determine executive function after exhaustive exercise.

METHODS

Thirty-two participants completed the cognitive tasks before and after an incremental exercise until exhaustion (exercise group: N = 18) or resting period (control group N = 14). The cognitive task was a combination of a Spatial Delayed-Response (Spatial DR) task and a Go/No-Go task, which requires executive function. Cerebral oxygenation and skin blood flow were monitored during the cognitive task over the prefrontal cortex. Venous blood samples were collected before and after the exercise or resting period, and blood catecholamines, serum brain-derived neurotrophic factor, insulin-like growth hormone factor 1, and blood lactate concentrations were analyzed.

RESULTS

In the exercise group, exhaustive exercise did not alter reaction time (RT) in the Go/No-Go task (pre: 861 ± 299 ms vs. post: 775 ± 168 ms) and the number of error trials in the Go/No-Go task (pre: 0.9 ± 0.7 vs. post: 1.8 ± 1.8) and the Spatial DR task (pre: 0.3 ± 0.5 vs. post: 0.8 ± 1.2). However, ΔRT was negatively correlated with Δcerebral oxygenation (r = -0.64, P = 0.004). Other physiological parameters were not correlated with cognitive performance. Venous blood samples were not directly associated with cognitive function after exhaustive exercise.

CONCLUSION

The present results suggest that recovery of regional cerebral oxygenation affects executive function after exhaustive exercise.

Effects of acute hypoxia on human cognitive processing: a study using ERPs and SEPs

Although hypoxia has the potential to impair the cognitive function, the effects of acute hypoxia on the high-order brain function (executive and/or inhibitory processing) and somatosensory ascending processing remain unknown. We tested the hypothesis that acute hypoxia impairs both motor executive and inhibitory processing and somatosensory ascending processing. Fifteen healthy subjects performed two sessions (sessions 1 and 2), consisting of electroencephalographic event-related potentials with somatosensory Go/No-go paradigms and somatosensory-evoked potentials (SEPs) under two conditions (hypoxia and normoxia) on different days. On 1 day, participants breathed room air in the first and second sessions of the experiment; on the other day, participants breathed room air in the first session, and 12% O₂ in the second session. Acute hypoxia reduced the peak amplitudes of Go-P300 and No-go-P300, and delayed the peak latency of Go-P300. However, no significant differences were observed in the peak amplitude or latency of N140, behavioral data, or the amplitudes and latencies of individual SEP components between the two conditions. These results suggest that acute hypoxia impaired neural activity in motor executive and inhibitory processing, and delayed higher cognitive processing for motor execution, whereas neural activity in somatosensory processing was not affected by acute hypoxia.NEW & NOTEWORTHY Hypoxia has the potential to impair the cognitive function, but the effects of acute hypoxia on the cognitive function remain debatable. We investigated the effects of acute hypoxia on human cognitive processing using electroencephalographic event-related potentials and somatosensory-evoked potentials. Acute normobaric hypoxia impaired neural activity in motor executive and inhibitory processing, but no significant differences were observed in neural activity in somatosensory processing.

Relationship between cognitive function and regulation of cerebral blood flow

Ageing is the primary risk factor for cognitive deterioration. Given that the cerebral blood flow (CBF) or regulation of cerebral circulation is attenuated in the elderly, it could be expected that ageing-induced cognitive deterioration may be affected by a decrease in CBF as a result of brain ischemia and energy depletion. CBF regulation associated with cerebral metabolism thus likely plays an important role in the preservation of cognitive function. However, in some specific conditions (e.g. during exercise), change in CBF does not synchronize with that of cerebral metabolism. Our recent study demonstrated that cognitive function was more strongly affected by changes in cerebral metabolism than by changes in CBF during exercise. Therefore, it remains unclear how an alteration in CBF or its regulation affects cognitive function. In this review, I summarize current knowledge on previous investigations providing the possibility of an interaction between regulation of CBF or cerebral metabolism and cognitive function.

Effect of acute hypoxia on cognition: A systematic review and meta-regression analysis

A systematic meta-regression analysis of the effects of acute hypoxia on the performance of central executive and non-executive tasks, and the effects of the moderating variables, arterial partial pressure of oxygen (PaO₂) and hypobaric versus normobaric hypoxia, was undertaken. Studies were included if they were performed on healthy humans; within-subject design was used; data were reported giving the PaO₂ or that allowed the PaO₂ to be estimated (e.g. arterial oxygen saturation and/or altitude); and the duration of being in a hypoxic state prior to cognitive testing was ≤6days. Twenty-two experiments met the criteria for inclusion and demonstrated a moderate, negative mean effect size (g=-0.49, 95% CI -0.64 to -0.34, p<0.001). There were no significant differences between central executive and non-executive, perception/attention and short-term memory, tasks. Low (35-60mmHg) PaO₂ was the key predictor of cognitive performance (R²=0.45, p<0.001) and this was independent of whether the exposure was in hypobaric hypoxic or normobaric hypoxic conditions.