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

Sensitivity of cognitive function tests to acute hypoxia in healthy subjects: a systematic literature review

Acute exposure to hypoxia can lead to cognitive impairment. Therefore, hypoxia may become a safety concern for occupational or recreational settings at altitude. Cognitive tests are used as a tool to assess the degree to which hypoxia affects cognitive performance. However, so many different cognitive tests are used that comparing studies is challenging. This structured literature evaluation provides an overview of the different cognitive tests used to assess the effects of acute hypoxia on cognitive performance in healthy volunteers. Less frequently used similar cognitive tests were clustered and classified into domains. Subsequently, the different cognitive test clusters were compared for sensitivity to different levels of oxygen saturation. A total of 38 articles complied with the selection criteria, covering 86 different cognitive tests. The tests and clusters showed that the most consistent effects of acute hypoxia were found with the Stroop test (where 42% of studies demonstrated significant abnormalities). The most sensitive clusters were auditory/verbal memory: delayed recognition (83%); evoked potentials (60%); visual/spatial delayed recognition (50%); and sustained attention (47%). Attention tasks were not particularly sensitive to acute hypoxia (impairments in 0%-47% of studies). A significant hypoxia level-response relationship was found for the Stroop test (p = 0.001), as well as three clusters in the executive domain: inhibition (p = 0.034), reasoning/association (p = 0.019), and working memory (p = 0.024). This relationship shows a higher test sensitivity at more severe levels of hypoxia, predominantly below 80% saturation. No significant influence of barometric pressure could be identified in the limited number of studies where this was varied. This review suggests that complex and executive functions are particularly sensitive to hypoxia. Moreover, this literature evaluation provides the first step towards standardization of cognitive testing, which is crucial for a better understanding of the effects of acute hypoxia on cognition.

Exercise-Induced Elevated BDNF Concentration Seems to Prevent Cognitive Impairment after Acute Exposure to Moderate Normobaric Hypoxia among Young Men

Memory impairment, reduced learning ability, decreased concentration, and psychomotor performance can be all signs of deleterious impact of hypoxia on cognitive functioning. In turn, physical exercise can improve performance and enhance cognitive functions. The purpose of this study was to investigate whether the potential positive effects of exercise performed under normobaric hypoxia can counteract the negative effects of hypoxia on cognitive function, and whether these changes correlate with brain-derived neurotrophic factor (BDNF) concentrations. Seventeen healthy subjects participated in a crossover study where they performed two sessions of single breathing bouts combined with moderate intensity exercise under two conditions: normoxia (NOR EX) and normobaric hypoxia (NH EX). To assess cognitive function, Stroop test was applied. There were no significant differences in any part of the Stroop interference test regardless of the conditions (NOR, NH), despite a statistical decrease in SpO2 (p < 0.0001) under normobaric hypoxic conditions. In addition, a statistical increase (p < 0.0001) in BDNF concentration was observed after both conditions. Acute exercise under normobaric hypoxia did not impair cognitive function despite a significant decrease in SpO2. Exercise in such conditions may offset the negative effects of hypoxia alone on cognitive function. This may be related to the significant increase in BDNF concentration and, as a consequence, positively affect the executive functions.

Executive Functions and Mood States in Athletes Performing Exercise Under Hypoxia

Hypoxia can impair cognitive performance, whereas exercise can enhance it. The effects of hypoxia on cognitive performance during exercise appear to be moderated by exercise duration and intensity and by severity and duration of hypoxia and cognitive task. In normal individuals, exercise under hypoxia can evoke adverse post-exercise mood states, such as tension and fatigue. However, little is known about the effects of hypoxia during exercise in trained athletes. The purpose of this study was to investigate how hypoxia affected executive functions and mood states, assessed, respectively, during and post-exercise and to explore the role of motivation moderators, such as inhibition and activation systems (BIS-BAS). Two different sessions of exercise in normoxia and hypoxia (FiO2 13%), each lasting 18 min, were randomly assigned in a counterbalanced order and administered to seventeen male athletes. During exercise bouts, participants performed a mental task (BST) aimed to produce cognitive interference and suppression. Reaction times and accuracy of responses were recorded. After 5 min, all participants completed two questionnaires assessing mood states (ITAMS) and incidence of symptoms potentially related to hypoxia (AMS-C). The results show that hypoxia impairs cognitive performance in terms of slower reaction times, but a high BAS attenuates this effect. Participants with high BAS show an equivalent cognitive performance under hypoxia and normoxia conditions. No effects were found on mood states. Further research is required to investigate the role of BAS, cognitive abilities, and mood states in prolonged hypoxic conditions.

The Methodological Quality of Studies Investigating the Acute Effects of Exercise During Hypoxia Over the Past 40 years: A Systematic Review

Exercise under hypoxia and the physiological impact compared to normoxia or hypoxia has gained attention in the last decades. However, methodological quality assessment of articles in this area is lacking in the literature. Therefore, this article aimed to evaluate the methodologic quality of trials studying exercise under hypoxia. An electronic search was conducted until December 2021. The search was conducted in PubMed, CENTRAL, and PEDro using the PICO model. (P) Participants had to be healthy, (I) exercise under normobaric or hypobaric hypoxia had to be (C) compared to exercise in normoxia or hypoxia on (O) any physiological outcome. The 11-item PEDro scale was used to assess the methodological quality (internal validity) of the studies. A linear regression model was used to evaluate the evolution of trials in this area, using the total PEDro score of the rated trials. A total of n = 81 studies met the inclusion criteria and were processed in this study. With a mean score of 5.1 ± 0.9 between the years 1982 and 2021, the mean methodological quality can be described as "fair." Only one study reached the highest score of 8/10, and n = 2 studies reached the lowest observed value of 3/10. The linear regression showed an increase of the PEDro score of 0.1 points per decade. A positive and small tendency toward increased methodologic quality was observed. The current results demonstrate that a positive and small tendency can be seen for the increase in the methodological quality in the field of exercise science under hypoxia. A "good" methodological quality, reaching a PEDro score of 6 points can be expected in the year 2063, using a linear regression model analysis. To accelerate this process, future research should ensure that methodological quality criteria are already included during the planning phase of a study.

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.

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.

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.

"Silent" Presentation of Hypoxemia and Cardiorespiratory Compensation in COVID-19

Severe hypoxemia presents variably, and sometimes silently, without subjective complaints of dyspnea. The adequacy of cardiovascular compensation for oxygen delivery to tissues should be a focus in all hypoxemic patients.

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.

Motor behavior-induced prefrontal cortex activation and episodic memory function

BACKGROUND

The objective of this paper was to evaluate the potential individual and combined effects of acute exercise coupled with bilateral interhemispheric activation on episodic memory function. Six experiments were conducted.

METHODS

Experiment 1 was a within-subject, counterbalanced experiment. Participants completed four visits, including 1) exercise and saccadic eye movements, 2) exercise only, 3) saccadic eye movements only, and 4) no exercise and no saccadic eye movements (control). A word-list memory assessment was employed, including a long-term (20-min delay) memory evaluation. In Experiment 2, we evaluated the effects of saccadic eye movements on prefrontal cortex oxygenation, a proxy for neuronal activity. Similarly, in our third experiment, we evaluated the effects of acute exercise on prefrontal cortex oxygenation. Thus, experiments 2 and 3 were employed to provide mechanistic insights from the results shown in experiment 1. Experiment 4 replicated Experiment 1, but instead of increasing prefrontal cortex activation via saccadic eye movements, we used a fist clenching protocol. Experiment 5 evaluated the effects of fist clenching on prefrontal cortex oxygenation.

RESULTS

Collectively, these 5 experimental studies showed that acute exercise (Experiment 1), saccadic eye movements (Experiment 1), and fist clenching (Experiment 4) enhanced memory function, and that acute exercise (Experiment 3), saccadic eye movements (Experiment 2) and fist clenching (Experiment 5) all increased prefrontal cortex oxygenation. Experiment 6 demonstrated that prefrontal cortex oxygenation was positively associated with episodic memory function.

CONCLUSION

These six experiments suggest that several behaviors, such as acute exercise, saccadic eye movements and fist clenching may improve memory function and may, potentially, do so via increases in prefrontal cortex oxygenation.

Combined effects of acute exercise and hypoxia on memory

No previous studies have evaluated the potential combined effects of acute exercise and acute hypoxia exposure on memory function, which was the purpose of this study. Twenty-five participants (Mage = 21.2 years) completed two laboratory visits in a counterbalanced order, involving 1) acute exercise (a 20-min bout of moderate-intensity exercise) and then 30 min of exposure to hypoxia (FIO2 = 0.12), and 2) exposure to hypoxia alone (FIO2 = 0.12) for 30 min. Following this, participants completed a cued-recall and memory interference task (AB/AC paradigm), assessing cued-recall memory (recall 1 and recall 2) and memory interference (proactive and retroactive interference). For cued-recall memory, we observed a significant main effect for condition, with Exercise + Hypoxia condition having significantly greater cued-recall performance than Hypoxia alone. Memory interference did not differ as a function of the experimental condition. This experiment demonstrates that engaging in an acute bout of exercise prior to acute hypoxia exposure had an additive effect in enhancing cued-recall memory performance.

Effects of Acute Normobaric Hypoxia on Memory Interference

Purpose: Previous research has evaluated the effects of acute hypoxia exposure on cognitive function, notably executive function. No studies, to date, have evaluated the effects of acute hypoxia exposure on memory interference, which was the purpose of this experiment. Methods: A within-subjects, counterbalanced experimental design was employed, with condition (hypoxia vs. normoxia) and time (immediate vs. delayed) being the independent variables. Participants (N = 21; M_age = 21.0 years) completed two laboratory visits, involving 30 min of exposure to either hypoxia (FIO₂ = 0.12) or normoxia (FIO₂ = 0.21). Following this, they completed a memory interference task (AB/AC paradigm), assessing immediate and delayed proactive and retroactive interference. Results: For retroactive interference, we observed a significant main effect for condition, F(1, 20) = 5.48, p = 0.03, ƞ² = 0.10, condition by time interaction, F(1, 20) = 4.96, p = 0.03, ƞ² = 0.01, but no main effect for time, F(1, 20) = 1.75, p = 0.20, ƞ² = 0.004. Conclusion: Our results demonstrate that acute hypoxia exposure was facilitative in reducing memory interference. We discuss these findings in the context of the potential therapeutic effects of acute hypoxia exposure on synaptic plasticity.

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.