Search Results (19)

Seasonal hypoxia in bottom waters of the Bohai Sea poses an escalating threat to marine ecosystems, yet monitoring it via satellite remote sensing continues to be challenging due to the inaccessibility of bottom layers. However, surface bio-optical signals do not instantaneously reflect variation in bottom-water dissolved oxygen (DO); instead, a distinct temporal lag exists between surface biological activity and its influence on bottom DO. Leveraging this insight, an inversion framework was established, integrating multi-source remote sensing data with decision tree-based machine learning models to estimate bottom-water DO concentration. We evaluated multiple lag intervals for satellite-derived bio-optical variables and adopted a 14-day lag as representative of the delayed impact of surface processes on bottom DO. An optimized feature set selected via a genetic algorithm (GA) was used to train the XGBoost model, which achieved high predictive performance (R² = 0.86, RMSE = 0.79 mg/L, MAPE = 8.89%). Interpretability analysis identified the sea surface temperature as the dominant driver of bottom-water DO variation in the Bohai Sea. The framework successfully reproduced the spatiotemporal variability in bottom DO from 2022 to 2024 in the Bohai Sea and captured the locations of summer hypoxic zones. Further analysis demonstrated that incorporating physically based bottom-layer variables substantially enhances model accuracy (R² = 0.89, RMSE = 0.68 mg/L, MAPE = 7.85%), underscoring their critical role in regulating bottom-water DO concentrations. Building on the established inversion framework and integrating extended in situ and satellite observations, we reconstruct the long-term temporal distribution of bottom DO in the Bohai Sea from 2014 to 2025, revealing the considerable potential of satellite data for monitoring bottom-water DO conditions in coastal seas. Full article

Background: Coronary artery disease remains the leading cause of morbidity and mortality in developed countries. Despite advances in treatment and standard rehabilitation, conventional programs may be monotonous and insufficiently engaging. Normobaric hypoxia, simulating high-altitude conditions, has emerged as a potential method to enhance cardiovascular adaptations in post-myocardial infarction (MI) patients. Objective: This study aimed to compare the efficacy and safety of exercise-based cardiac rehabilitation performed under normobaric hypoxia corresponding to altitudes of 2000 m and 3000 m above sea level in patients after MI treated with percutaneous coronary intervention (PCI). Methods: A total of 61 male post-MI patients (mean age 60.4 ± 8.9 years) were randomized into two groups: training under simulated altitudes of 2000 m (n = 35) or 3000 m (n = 26). The 22-day program consisted of interval ergometer sessions. Pre- and post-intervention assessments included cardiopulmonary exercise testing (CPET), echocardiography, and tissue Doppler imaging (TDI). Results: Both groups demonstrated significant improvements in exercise tolerance. Training at 2000 m significantly increased test duration (r = 0.735) and peak heart rate (r = 0.467). At 3000 m, additional benefits were observed, including improvements in metabolic equivalent (r = 0.861), peak oxygen consumption (d = 0.81), and reduction in respiratory exchange ratio (r = 0.682). Intergroup analysis revealed moderate differences favoring the 3000 m group in MET, breathing frequency, and RER. Echocardiography showed beneficial remodeling in both groups, with improvements in LV dimensions, ejection fraction, and MAPSE. Notably, training at 2000 m resulted in more consistent echocardiographic benefits compared to 3000 m. Conclusions: Cardiac rehabilitation under normobaric hypoxia is effective and safe in stable post-MI patients. Training at 3000 m provides greater improvements in exercise tolerance, while 2000 m confers more favorable effects on cardiac structure and function. These findings suggest that moderate hypoxic exposure (2000 m) may represent an optimal balance between efficacy and safety in post-MI rehabilitation. Full article

The relationship between exercise and immune function has been widely studied, yet findings remain inconsistent regarding how different exercise modalities and intensities influence acute and chronic immunological responses. Previous reviews have often focused on single exercise types or limited outcomes, leaving a gap for an integrated synthesis. This narrative review aims to address this gap by summarizing and comparing immunological effects across aerobic exercise, resistance training, high-intensity interval training (HIIT), blood flow restriction (BFR), isometric exercise, mind–body interventions, and hypoxic training. A structured narrative approach was adopted. Literature published between January 2000 and December 2024 was searched in PubMed, Scopus, and Web of Science. Experimental and observational studies on humans and animal models were included, with study selection and data extraction performed by two reviewers. Findings were synthesized thematically by exercise modality to capture both acute and chronic immune responses. Twenty-four eligible studies were identified. Aerobic and mind–body exercises consistently demonstrated anti-inflammatory and immunoprotective effects, including increased IL-10 production, improved T cell profiles, and reduced inflammatory markers. Isometric training showed favorable modulation of cytokines and T cell balance, while resistance training evidence was limited but suggested cortisol-lowering benefits. HIIT, BFR, and hypoxic exercise produced mixed results, often combining transient pro-inflammatory responses with immunological benefits. Acute and chronic immunological responses to exercise are highly modality- and intensity-dependent. Aerobic and mind–body interventions provide the most consistent benefits, whereas HIIT, BFR, and hypoxic training show variable effects. Further high-quality trials are needed to clarify mechanisms and guide exercise-based immune recommendations. Full article

Background: Repeated high-intensity intervals under normoxic (NOR) and hypoxic (HYP) conditions is a training strategy used by athletes. Although different protocols have been used, the effect of longer recovery between repetitions is unclear. In addition, information on the effect of repeated high-intensity intervals on HYP in women is scarce. Aims: To analyse the differences between sexes and between conditions (NOR and HYP) in Repeated Wingate (RW) performance and neuromuscular fatigue in triathletes. Methods: A total of 12 triathletes (men: n = 7, 23.00 ± 4.04 years; women: n = 5, 20.40 ± 3.91) participated in this randomised, blinded, crossover study. In two separate sessions over seven days, participants performed 3 × 30” all out with 7′ of recovery in randomised NOR (fraction of inspired oxygen: ≈20%; ≈300 m altitude) and HYP (fraction of inspired oxygen: ≈15.5%; ≈2500 m altitude) conditions. Before and after RW, vertical jump tests were performed to assess neuromuscular fatigue. Oxygen saturation, power, perceived exertion, muscle soreness and heart rate parameters were assessed. Results: Significant differences were reported between sexes in the parameters of vertical jump, oxygen saturation, RW performance and heart rate (p < 0.05). However, between conditions (NOR and HYP), only differences in oxygen saturation were reported (p < 0.05). No significant differences were reported between conditions (NOR and HYP) in RW performance, neuromuscular fatigue, muscle soreness and perception of exertion. Conclusions: A 3 × 30” RW protocol with 7′ recovery in HYP could have no negative consequences on performance, neuromuscular fatigue and perception of exertion in triathletes compared to NOR, independently of sex. Full article

This study explores the effects of normobaric hypoxia and intermittent hypoxic training (IHT) on the physiological condition of the cardiac muscle in swimmers. Hypoxia has been reported to elicit both beneficial and adverse changes in the cardiovascular system, but its impact on the myocardium during acute exercise and altitude/hypoxic training remains less understood. We aimed to determine how a single bout of intense interval exercise and a four-week period of high-intensity endurance training under normobaric hypoxia affect cardiac marker activity in swimmers. Sixteen young male swimmers were divided into two groups: one undergoing training in hypoxia and the other in normoxia. Cardiac markers, including troponin I and T (cTnI and cTnT), heart-type fatty acid-binding protein (H-FABP), creatine kinase-MB isoenzyme (CK-MB), and myoglobin (Mb), were analyzed to assess the myocardium’s response. We found no significant differences in the physiological response of the cardiac muscle to intense physical exertion between hypoxia and normoxia. Four weeks of IHT did not alter the resting levels of cTnT, cTnI, and H-FABP, but it resulted in a noteworthy decrease in the resting concentration of CK-MB, suggesting enhanced cardiac muscle adaptation to exercise. In contrast, a reduction in resting Mb levels was observed in the control group training in normoxia. These findings suggest that IHT at moderate altitudes does not adversely affect cardiac muscle condition and may support cardiac muscle adaptation, affirming the safety and efficacy of IHT as a training method for athletes. Full article

This study aimed to comprehensively evaluate the effects of intermittent hypoxic training (IHT) on anaerobic performance in young, untrained men. Young men (n = 48) were randomly divided into two training groups and a control group. The training groups performed the same submaximal interval training (three times a week for 4 weeks) in normoxia (200 m asl) or in hypoxia (IHT) (FIO₂ = 14.4%). The workloads for the interval training corresponded to the intensity of the ventilatory thresholds determined in a graded test. Participants performed a supramaximal all-out sprint test in normoxia twice: before and after the training. Significant improvement in both absolute peak power (p < 0.001; ES = 0.34) and relative peak power (p < 0.001; ES = 0.54) was noted after IHT. Similar changes were not observed either after training in normoxia (p = 0.14 and p = 0.26, for absolute and relative peak power, respectively) or in the control group (p = 0.34 and p = 0.51, for absolute and relative peak power, respectively). Compared to baseline, there were no significant changes in the absolute and relative mean power of either group after training. Intermittent hypoxic training in young, untrained men can be effective in improving their peak power, but does not significantly affect their mean power. Full article

High-intensity interval training (HIIT) and hyperbaric oxygen therapy (HBOT) induce reactive oxygen species (ROS) formation and have immunomodulatory effects. The lack of readily available biomarkers for assessing the dose–response relationship is a challenge in the clinical use of HBOT, motivating this feasibility study to evaluate the methods and variability. The overall hypothesis was that a short session of hyperbaric oxygen (HBO₂) would have measurable effects on immune cells in the same physiological range as shown in HIIT; and that the individual response to these interventions can be monitored in venous blood and/or peripheral blood mononuclear cells (PBMCs). Ten healthy volunteers performed two interventions; a 28 min HIIT session and 28 min HBO₂ in a crossover design. We evaluated bulk RNA sequencing data from PBMCs, with a separate analysis of mRNA and microRNA. Blood gases, peripheral venous oxygen saturation (SpvO₂), and ROS levels were measured in peripheral venous blood. We observed an overlap in the gene expression changes in 166 genes in response to HIIT and HBO₂, mostly involved in hypoxic or inflammatory pathways. Both interventions were followed by downregulation of several NF-κB signaling genes in response to both HBO₂ and HIIT, while several interferon α/γ signaling genes were upregulated. Only 12 microRNA were significantly changed in HBO₂ and 6 in HIIT, without overlap between interventions. ROS levels were elevated in blood at 30 min and 60 min compared to the baseline during HIIT, but not during/after HBO₂. In conclusion, HBOT changed the gene expression in a number of pathways measurable in PBMC. The correlation of these changes with the dose and individual response to treatment warrants further investigation. Full article

A deep learning classifier is proposed for grading hypoxic-ischemic encephalopathy (HIE) in neonates. Rather than using handcrafted features, this architecture can be fed with raw EEG. Fully convolutional layers were adopted both in the feature extraction and classification blocks, which makes this architecture simpler, and deeper, but with fewer parameters. Here, two large (335 h and 338 h, respectively) multi-center neonatal continuous EEG datasets were used for training and testing. The model was trained based on weak labels and channel independence. A majority vote method was used for the post-processing of the classifier results (across time and channels) to increase the robustness of the prediction. A dimension reduction tool, UMAP, was used to visualize the model classification effect. The proposed system achieved an accuracy of 86.09% (95% confidence interval: 82.41–89.78%), an MCC of 0.7691, and an AUC of 86.23% on the large unseen test set. Two convolutional neural network architectures which utilized time-frequency distribution features were selected as the baseline as they had been developed or tested on the same datasets. A relative improvement of 23.65% in test accuracy was obtained as compared with the best baseline. In addition, if only one channel was available, the test accuracy was only reduced by 2.63–5.91% compared with making decisions based on the eight channels. Full article

Background: Emerging evidence suggests that the outcomes of hypoxia training may be influenced by various factors, contingent upon the chosen method, such as chamber, tent, or mask. This study aimed to examine how different training methods influence the effects of Repeated Sprints in Hypoxia (RSH) training. Methods: Sixteen well-trained cyclists were divided into two groups, experimental (tent; n = 8) and control (mask; n = 8), and carried out eight RSH sessions for four weeks. Training sessions consisted of three bouts of high-intensity sprints using a cycle ergometer. The indoor ambient conditions (CO₂, temperature, and humidity), performance variables (power and relative power output), arterial oxygen saturation, local muscle oxygen of vastus lateralis, heart rate, core temperature, and physiological variables (perception of effort) were measured in each training session. Results: The experimental group reported significantly higher CO₂ (p < 0.001 ES = 0.784), humidity levels (p < 0.001 ES = 0.750), thermal discomfort (p = 0.003 ES = 0.266), dehydration (p 0.025 ES = 0.097), heart rate (p = 0.017 ES = 0.113), and lower muscle oxygen amplification (p = 0.002 ES = 0.181) than the control group. Conclusion: According to the responses observed, interval training performed under hypoxic conditions inside a chamber induces a more severe physiological response. Full article

Objectives: This study describes the effects of interval hypoxic training and electrical muscle stimulation (EMS) technology on human productivity with the following metrics: biochemical indices, cognitive abilities, changes in oxygenated (HbO) and deoxygenated (Hb) hemoglobin concentrations over the prefrontal cortex, and functional connectivity via electroencephalography (EEG). Methods: All measurements according to the described technology were made before the start of training and one month later, right after it ended. The study involved middle-aged Indo-European men. Specifically, there were 14, 15, and 18 participants in the control, hypoxic, and EMS groups, respectively. Results: EMS training improved reactions and nonverbal memory but decreased attention scores. Functional connectivity decreased in the EMS group while it increased in the hypoxic group. A result of the interval normobaric hypoxic training (IHT) was significantly improved contextual memory, with a p-value = 0.08. Conclusions: It was found that EMS training is more likely to cause stress on the body than positively affect cognitive functions. At the same time, interval hypoxic training can be considered a promising direction for increasing human productivity. The data obtained during the study can also help in the timely diagnosis of insufficient or overestimated indicators of biochemistry. Full article

Arterial stiffness, an age-dependent phenomenon, is improved with exercise, which in turn may prevent cardiovascular diseases in women. However, there is a lack of consolidated information on the impact of exercise on arterial stiffness among healthy women. The aim of this review was to (i) analyse the effect of exercise on arterial stiffness in healthy young, middle-aged, and older women, and (ii) recommend types, intensity, and frequency for each age group. Database searches on PubMed, ScienceDirect, Web of Science, and Scopus were conducted using PRISMA guidelines until September 2022. The keywords were: exercise, women/female, and arterial stiffness. The inclusion criteria were: healthy women, supervised exercise, and arterial stiffness measures. Study quality and bias were assessed using the PEDro scale. Fifty-one papers were classified into young (n = 15), middle-aged (n = 14), and older (n = 22) women. Improvements in arterial stiffness were observed among: young women (Pulse Wave Velocity, PWV: 4.9–6.6 m/s), following an 8-week high-intensity aerobic (3 days/week) or hypoxic high-intensity interval training; middle-aged women (PWV: 5.1–7.9 m/s), aerobic exercise with moderate intensity or stretching exercise at “moderate to heavy” (Borg Scale), 20–30 s per site, 10 s of rest interval for 30 min; and for older women (PWV: 7.9–15.6 m/s), resistance training at light intensity, aerobic exercise at any intensity, or a combination of the two exercises. This review shows that arterial stiffness increases with age in healthy women and has an inverse relationship with exercise intensity. Therefore, when prescribing exercise to improve arterial stiffness, age and arterial stiffness measures should be accounted for. Full article

The present study aimed to determine the effect of high intensity interval training (HIIT) in hypoxia on maximal oxygen uptake (VO_2max) compared with HIIT in normoxia with a Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA)-accordant meta-analysis and meta-regression. Studies which measured VO_2max following a minimum of 2 weeks intervention featuring HIIT in hypoxia versus HIIT in normoxia were included. From 119 originally identified titles, nine studies were included (n = 194 participants). Meta-analysis was conducted on change in (∆) VO_2max using standardised mean difference (SMD) and a random effects model. Meta-regression examined the relationship between the extent of environmental hypoxia (fractional inspired oxygen [FiO₂]) and ∆VO_2max and intervention duration and ∆VO_2max. The overall SMD for ∆VO_2max following HIIT in hypoxia was 1.14 (95% CI = 0.56–1.72; p < 0.001). Meta-regressions identified no significant relationship between FiO₂ (coefficient estimate = 0.074, p = 0.852) or intervention duration (coefficient estimate = 0.071, p = 0.423) and ∆VO_2max. In conclusion, HIIT in hypoxia improved VO_2max compared to HIIT in normoxia. Neither extent of hypoxia, nor training duration modified this effect, however the range in FiO₂ was small, which limits interpretation of this meta-regression. Moreover, training duration is not the only training variable known to influence ∆VO_2max, and does not appropriately capture total training stress or load. This meta-analysis provides pooled evidence that HIIT in hypoxia may be more efficacious at improving VO_2max than HIIT in normoxia. The application of these data suggest adding a hypoxic stimuli to a period of HIIT may be more effective at improving VO_2max than HIIT alone. Therefore, coaches and athletes with access to altitude (either natural or simulated) should consider implementing HIIT in hypoxia, rather than HIIT in normoxia where possible, assuming no negative side effects. Full article

Hypobaric hypoxia (HH) seems to lead to different responses compared to normobaric hypoxia (NH) during physical conditioning. The aim of the study was to analyze the hormonal and circulating ion responses after performing high-intensity resistance training with different inter-set rest under HH and NH condition. Sixteen male volunteers were randomly divided into two training groups. Each group completed two counterbalanced resistance training sessions (three sets × ten repetitions, remaining two repetitions in reserve), with both one- and two-minute inter-set rest, under HH and NH. Blood samples were obtained to determine hormones and circulating ions (Ca²⁺, Pi, and HCO₃⁻) at baseline and after training sessions (5, 10, and 30 min). Resistance training with one-minute rest caused greater hormonal stress than with two-minute rest in cortisol and growth hormone, although the hypoxic environmental condition did not cause any significant alterations in these hormones. The short inter-set rest also caused greater alterations in HCO₃⁻ and Pi than the longer rest. Additionally, higher levels of Ca²⁺ and Pi, and lower levels of HCO₃⁻, were observed after training in HH compared to NH. Metabolic and physiological responses after resistance training are mediated by inter-set rest intervals and hypoxic environmental condition. According to the alterations observed in the circulating ions, HH could cause greater muscular fatigue and metabolic stress than NH. Full article

High-intensity interval training (HIIT) and low-oxygen exposure may inhibit the secretion of appetite-stimulating hormones, suppress appetite, and inhibit dietary intake. Physiological changes affecting appetite are frequent and include appetite hormone (ghrelin, leptin, PYY, and GLP-1) effects and the subjective loss of appetite, resulting in nutritional deficiencies. This paper is a narrative review of the literature to verify the HIIT effect on appetite regulation mechanisms and discusses the possible relationship between appetite effects and the need for high-intensity exercise training in a hypoxic environment. We searched MEDLINE/PubMed and the Web of Science databases, as well as English articles (gray literature by Google Scholar for English articles) through Google Scholar, and the searched studies primarily focused on the acute effects of exercise and hypoxic environmental factors on appetite, related hormones, and energy intake. In a general normoxic environment, regular exercise habits may have accustomed the athlete to intense training and, therefore, no changes occurred in their subjective appetite, but there is a significant effect on the appetite hormones. The higher the exercise intensity and the longer the duration, the more likely exercise is to cause exercise-induced appetite loss and changes in appetite hormones. It has not been clear whether performing HIIT in a hypoxic environment may interfere with the exerciser’s diet or the nutritional supplement intake as it suppresses appetite, which, in turn, affects and interferes with the recovery efficiency after exercise. Although appetite-regulatory hormones, the subjective appetite, and energy intake may be affected by exercise, such as hypoxia or hypoxic exercise, we believe that energy intake should be the main observable indicator in future studies on environmental and exercise interventions. Full article

Benefits of performing sprint interval training (SIT) under hypoxic conditions on improving cardiorespiratory fitness and body composition have been well-documented, yet data is still lacking regarding affective responses to SIT under hypoxia. This study aimed to compare affective responses to SIT exercise under different oxygen conditions. Nineteen active males participated in three sessions of acute SIT exercise (20 repetitions of 6 s of all-out cycling bouts interspersed with 15 s of passive recovery) under conditions of normobaric normoxia (SL: PIO₂ 150 mmHg, FIO₂ 0.209), moderate hypoxia (MH: PIO₂ 117 mmHg, FIO₂ 0.154, simulating an altitude corresponding to 2500 m), and severe hypoxia (SH: PIO₂ 87 mmHg, FIO₂ 0.112, simulating an altitude of 5000 m) in a randomized order. Perceived exertions (RPE), affect, activation, and enjoyment responses were recorded before and immediately after each SIT session. There were no significant differences across the three conditions in RPE or the measurements of affective responses, despite a statistically lower SpO₂ (%) in severe hypoxia. Participants maintained a positive affect valence and reported increased activation in all the three SIT conditions. Additionally, participants experienced a medium level of enjoyment after exercise as indicated by the exercise enjoyment scale (EES) and physical activity enjoyment scale (PACES). These results indicated that performing short duration SIT exercise under severe hypoxia could be perceived as pleasurable and enjoyable as performing it under normoxia in active male population. Full article