High-Intensity Interval Training in Normobaric Hypoxia Improves Cardiorespiratory Fitness in Overweight Chinese Young Women

Sprint training in hypoxia and with blood flow restriction: Controversies and perspectives

This narrative review assesses the effects of repeated sprint training (RST) in hypoxia (RSH) and blood flow restriction (BFR) methods on skeletal muscle adaptations and performance. Current literature suggests that RSH promotes metabolic modifications in muscle cells, especially driven by reactive oxygen species production, HIF-1α stabilization, and changes in metabolism. Training with BFR promotes metabolite accumulation in working muscles due to limited blood flow, however, cellular mechanisms affected by BFR during RST are less explored. Data highlight that RSH improves repeated sprint ability (RSA) in several sport disciplines (e.g. rugby, tennis, soccer, cross-country skiing). However, recent studies showed that addition of hypoxia or BFR during RST did not promote supplementary benefits on aerobic performance, force-velocity power profile, and V ˙ O 2 max . Nonetheless, gains in V ˙ O 2 max were observed during sprint interval training protocols when BFR was applied during recovery between sets. Finally, recent studies highlighted that RSH can improve RSA in a short period. Thus, RSH and sprint training with BFR may be useful for sports disciplines requiring high glycolytic demand and can promote gains in RSA in a short window. Further studies must be encouraged to better understand the biological consequences of adding such stimuli to exercise, especially BFR, on long-term adaptation.

The Impact of Intermittent Hypoxic Training on Aerobic Capacity and Biometric-Structural Indicators among Obese Women-A Pilot Study

BACKGROUND

Obesity, a common lifestyle-related condition, is correlated with factors like inadequate physical activity. Its connection to diverse health issues presents a significant challenge to healthcare. This pilot study investigated the effects of hypoxic training on aerobic capacity and biometric-structural indicators in obese women. The secondary objective was to determine the feasibility, effectiveness, and safety of the planned research procedures and their potential for larger-scale implementation.

MATERIAL AND METHODS

Forty-one non-trained women with first-degree obesity were randomly assigned to even normobaric hypoxic training (H + E), normoxic training (E), passive exposure to hypoxia (H), and a control group (C). Training sessions were conducted three times a week for four weeks (12 training sessions). Body composition parameters were assessed, metabolic thresholds were determined, and maximal oxygen consumption (VO2max) was measured before and after interventions.

RESULTS

The results demonstrated that training in hypoxic conditions significantly affected somatic parameters, with the H + E group achieving the best outcomes in terms of weight reduction and improvements in body composition indicators (p < 0.001). Normoxic training also induced a positive impact on body weight and body composition, although the results were less significant compared to the H + E group (p < 0.001). Additionally, training in hypoxic conditions significantly improved the aerobic capacity among the participants (p < 0.001). The H + E group achieved the best results in enhancing respiratory endurance and oxygen consumption (p < 0.001).

CONCLUSIONS

The results of this pilot study suggest, that hypoxic training can be effective for weight reduction and improving the aerobic capacity in obese women. Despite study limitations, these findings indicate that hypoxic training could be an innovative approach to address obesity and related conditions. Caution is advised in interpreting the results, considering both the strengths and limitations of the pilot study. Before proceeding to a larger-scale study, the main study should be expanded, including aspects such as dietary control, monitoring physical activity, and biochemical blood analysis.

Aerobic Exercise Training Under Normobaric Hypoxic Conditions to Improve Glucose and Lipid Metabolism in Overweight and Obese Individuals: A Systematic Review and Meta-Analysis

Guo, Hai, Linjie Cheng, Dilihumaier Duolikun, and Qiaoling Yao. Aerobic exercise training under normobaric hypoxic conditions to improve glucose and lipid metabolism in overweight and obese individuals: a systematic review and meta-analysis. High Alt Med Biol. 24:312-320, 2023. Background: Obesity is a critical public health issue around the world, reaching epidemic proportions in some countries. However, only a few studies have examined the effects of hypoxic training on metabolic parameters in an obese population. This systematic review and meta-analysis aimed to determine the effects of aerobic exercise training under normobaric hypoxic conditions versus normoxic training in improving glucose and lipid metabolism in obese individuals. Methods: A systematic search of PubMed, EMBASE, Web of Science, and Wan Fang databases (up to August 2021) was performed to identify randomized controlled trials (RCTs) of overweight or obese human subjects eligible for inclusion. Main study endpoints were changes in body mass index (BMI), waist/hip (W/H) ratio, leptin, blood glucose and insulin levels, as well as blood lipids between hypoxic and normoxic conditioning. Results: Fourteen RCTs with a total of 413 subjects qualified for inclusion. Pooled analyses revealed that BMI (d = 0.38), W/H ratio (d = 0), blood glucose (d = 0.01), and triglyceride (d = -2.27) were not significantly different between aerobic exercise training under hypoxic and normoxic conditions. However, significant differences were found in heart rate at rest (d = -4.50) between aerobic exercise training under hypoxic versus normoxic conditions. Conclusions: In conclusion, no significant benefits were noted in aerobic exercise training under hypoxic conditions over normoxic conditions in overweight or obese individuals. However, the maximum training heart rate mm was significantly higher under hypoxic conditions than under normoxic conditions. Future studies with larger samples controlling for exercise-related parameters, and addressing the potential modifying effects of level of hypoxia, sex, or age on the role of hypoxic exercise training are warranted. PROSPERO registration number: CRD42020221680.

Comparative efficacy of various hypoxic training paradigms on maximal oxygen consumption: A systematic review and network meta-analysis

Background

Enhancement in maximal oxygen consumption (VO2max) induced by hypoxic training is important for both athletes and non-athletes. However, the lack of comparison of multiple paradigms and the exploration of related modulating factors leads to the inability to recommend the optimal regimen in different situations. This study aimed to investigate the efficacy of seven common hypoxic training paradigms on VO2max and associated moderators.

Methods

Electronic (i.e., five databases) and manual searches were performed, and 42 studies involving 1246 healthy adults were included. Pairwise meta-analyses were conducted to compare different hypoxic training paradigms and hypoxic training and control conditions. The Bayesian network meta-analysis model was applied to calculate the standardised mean differences (SMDs) of pre-post VO2max alteration among hypoxic training paradigms in overall, athlete, and non-athlete populations, while meta-regression analyses were employed to explore the relationships between covariates and SMDs.

Results

All seven hypoxic training paradigms were effective to varying degrees, with SMDs ranging from 1.45 to 7.10. Intermittent hypoxia interval training (IHIT) had the highest probability of being the most efficient hypoxic training paradigm in the overall population and athlete subgroup (42%, 44%), whereas intermittent hypoxic training (IHT) was the most promising hypoxic training paradigm among non-athletes (66%). Meta-regression analysis revealed that saturation hours (coefficient, 0.004; P = 0.038; 95% CI [0.0002, 0.0085]) accounted for variations of VO2max improvement induced by IHT.

Conclusion

Efficient hypoxic training paradigms for VO2max gains differed between athletes and non-athletes, with IHIT ranking best for athletes and IHT for non-athletes. The practicability of saturation hours is confirmed with respect to dose-response issues in the future hypoxic training and associated scientific research.

Registration

This study was registered in the PROSPERO international prospective register of systematic reviews (CRD42022333548).

Elucidating the primary mechanisms of high-intensity interval training for improved cardiac fitness in obesity

Obesity is a global and rising multifactorial pandemic associated with the emergence of several comorbidities that are risk factors for malignant cardiac remodeling and disease. High-intensity interval training (HIIT) has gained considerable attention due to its favorable outcomes of cardiometabolic health in individuals with overweight or obese. The primary aim of this review is to discuss the fundamental processes through which HIIT improves cardiac impairment in individuals with obesity to develop viable treatments for obesity management. In this review, a multiple database search and collection were conducted from the earliest record to January 2013 for studies included the qualitative component of HIIT intervention in humans and animals with overweight/obesity related to cardiac remodeling and fitness. We attempt to integrate the main mechanisms of HIIT in cardiac remolding improvement in obesity into an overall sequential hypothesis. This work focus on the ameliorative effects of HIIT on obesity-induced cardiac remodeling with respect to potential and pleiotropic mechanisms, including adipose distribution, energy metabolism, inflammatory response, insulin resistance, and related risk profiles in obesity. In conclusion, HIIT has been shown to reduce obesity-induced risks of cardiac remodeling, but the long-term effects of HIIT on obesity-induced cardiac injury and disease are presently unknown. Collective understanding highlights numerous specific research that are needed before the safety and effectiveness of HIIT can be confirmed and widely adopted in patient with obesity.

Moderate to Vigorous-intensity Continuous Training versus High-intensity Interval Training for improving VO2max in women: A systematic review and meta-analysis

Traditional continuous training and high-intensity interval training (HIIT) can increase maximal oxygen uptake (V̇O_2max). However, there is conflicting evidence regarding which form of training demonstrates the greatest improvements to V̇O_2max, and data in women is sparse. We conducted a systematic review and meta-analyses to assess whether moderate to vigorous-intensity continuous training (MVICT) or HIIT was superior at improving V̇O_2max in women. Randomised controlled and parallel studies examined the influence of MVICT and/or HIIT on V̇O_2max in women. There was no statistical difference in V̇O_2max improvements after training between women in the MVICT and HIIT cohorts (mean difference [MD]: -0.42, 95%CI: -1.43 to 0.60, p>0.05). Both MVICT and HIIT increased V̇O_2max from baseline (MD: 3.20, 95% CI: 2.73 to 3.67 and MD: 3.16, 95% CI 2.09 to 4.24, respectively, p<0.001). Greater improvements in V̇O_2max were observed in women who participated in more training sessions in both training formats. Long-HIIT was superior to short-HIIT protocols at increasing V̇O_2max. Although MVICT and long-HIIT sessions elicited greater increases in V̇O_2max in younger women compared to short-HIIT protocols, these differences were negligible in older women. Our findings suggest MVICT and HIIT are equally effective strategies for improving V̇O_2max and indicate an effect of age on its response to training in women.

Mechanisms for Combined Hypoxic Conditioning and Divergent Exercise Modes to Regulate Inflammation, Body Composition, Appetite, and Blood Glucose Homeostasis in Overweight and Obese Adults: A Narrative Review

Obesity is a major global health issue and a primary risk factor for metabolic-related disorders. While physical inactivity is one of the main contributors to obesity, it is a modifiable risk factor with exercise training as an established non-pharmacological treatment to prevent the onset of metabolic-related disorders, including obesity. Exposure to hypoxia via normobaric hypoxia (simulated altitude via reduced inspired oxygen fraction), termed hypoxic conditioning, in combination with exercise has been increasingly shown in the last decade to enhance blood glucose regulation and decrease the body mass index, providing a feasible strategy to treat obesity. However, there is no current consensus in the literature regarding the optimal combination of exercise variables such as the mode, duration, and intensity of exercise, as well as the level of hypoxia to maximize fat loss and overall body compositional changes with hypoxic conditioning. In this narrative review, we discuss the effects of such diverse exercise and hypoxic variables on the systematic and myocellular mechanisms, along with physiological responses, implicated in the development of obesity. These include markers of appetite regulation and inflammation, body conformational changes, and blood glucose regulation. As such, we consolidate findings from human studies to provide greater clarity for implementing hypoxic conditioning with exercise as a safe, practical, and effective treatment strategy for obesity.

Effects of exercise training in hypoxia versus normoxia on fat-reducing in overweight and/or obese adults: A systematic review and meta-analysis of randomized clinical trials

Objective: Fat loss theory under various oxygen conditions has been disputed, and relevant systematic review studies are limited. This study is a systematic review and meta-analysis to assess whether hypoxic exercise training (HET) leads to superior fat-reducing compared with normoxic exercise training (NET).

Methods: We searched PubMed, Web of Science, CNKI, ProQuest, Google Scholar, Cochrane Library, and EBSCOhost from inception to June 2022 for articles comparing the effects of hypoxic and normoxic exercise on body composition indicators, glycometabolism, and lipometabolism indicators in obese and overweight adults. Only randomized controlled trials (RCTs) were included. The effect sizes were expressed as standardized mean difference (SMD) and 95% confidence intervals (CI). Between-study heterogeneity was examined using the I² test and evaluated publication bias via Egger’s regression test. The risk of bias assessment was performed for each included trial using Cochrane Evaluation Tool second generation. The meta-analysis was performed by using R 4.1.3 and RevMan 5.3 analytic tools.

Results: A total of 19 RCTs with 444 subjects were analyzed according to the inclusion and exclusion criteria. Among them, there were 14 English literature and five Chinese literature. No significant difference in body composition (SMD -0.10, 95% CI -0.20 to -0.01), glycometabolism and lipid metabolism (SMD -0.01, 95% CI -0.13 to -0.10) has been observed when comparing the HET and NET groups. We only found low heterogeneity among trials assessing glycometabolism and lipometabolism (I² = 20%, p = 0.09), and no publication bias was detected.

Conclusion: The effects of HET and NET on fat loss in overweight or obese people are the same. The application and promotion of HET for fat reduction need further exploration.

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.

Therapeutic approach for digestive system cancers and potential implications of exercise under hypoxia condition: what little is known? a narrative review

BACKGROUND

Cancer, like other chronic pathologies, is associated with the presence of hypoxic regions due to the uncontrolled cell growth. Under this pathological hypoxic condition, various molecular signaling pathways are activated to ensure cell survival, such as those that govern angiogenesis, erythropoiesis, among others. These molecular processes are very similar to the physiological response caused by exposure to altitude (natural hypobaric systemic hypoxia), the use of artificial hypoxia devices (systemic normobaric simulated hypoxia) or the delivery of vascular occlusion to the extremities (also called local hypoxia by the blood flow restriction technique). "Tumor hypoxia" has gained further clinical importance due to its crucial role in both tumor progression and resistance to treatment. However, the ability to manipulate this pathway through physical exercise and systemic hypoxia-mediated signaling pathways could offer an important range of therapeutic opportunities that should be further investigated.

METHODS

This review is focused on the potential implications of systemic hypoxia combined with exercise in digestive system neoplasms prognosis. Articles included in the review were retrieved by searching among the three main scientific databases: PubMed, Scopus, and Embase.

FINDINGS

The findings of this review suggest that exercise performed under systemic hypoxic conditions could have a positive impact in prognosis and quality of life of the population with digestive system cancers.

CONCLUSIONS

Further studies are needed to consider this paradigm as a new potential intervention in digestive oncological population.

Exposure to Normobaric Hypoxia Combined with a Mixed Diet Contributes to Improvement in Lipid Profile in Trained Cyclists

This study aimed to analyze the effects of live high-train low method (LH-TL) and intermittent hypoxic training (IHT) with a controlled mixed diet on lipid profile in cyclists. Thirty trained male cyclists at a national level with at least six years of training experience participated in the study. The LH-TL group was exposed to hypoxia (FiO2 = 16.5%) for 11-12 h a day and trained under normoxia for 3 weeks. In the IHT group, participants followed the IHT routine three times a week under hypoxia (FiO2 = 16.5%) at lactate threshold intensity. The control group (N) lived and trained under normoxia. The results showed that the 3-week LH-TL method significantly improved all lipid profile variables. The LH-TL group showed a significant increase in HDL-C by 9.0% and a decrease in total cholesterol (TC) by 9.2%, LDL-C by 18.2%, and triglycerides (TG) by 27.6%. There were no significant changes in lipid profiles in the IHT and N groups. ∆TG and ∆TC were significantly higher in the LH-TL group compared to the N group. In conclusion, hypoxic conditions combined with a mixed diet can induce beneficial changes in lipid profile even in highly trained athletes. The effectiveness of the hypoxic stimulus is closely related to the hypoxic training method.

Altitude, Exercise, and Skeletal Muscle Angio-Adaptive Responses to Hypoxia: A Complex Story

Hypoxia, defined as a reduced oxygen availability, can be observed in many tissues in response to various physiological and pathological conditions. As a hallmark of the altitude environment, ambient hypoxia results from a drop in the oxygen pressure in the atmosphere with elevation. A hypoxic stress can also occur at the cellular level when the oxygen supply through the local microcirculation cannot match the cells’ metabolic needs. This has been suggested in contracting skeletal myofibers during physical exercise. Regardless of its origin, ambient or exercise-induced, muscle hypoxia triggers complex angio-adaptive responses in the skeletal muscle tissue. These can result in the expression of a plethora of angio-adaptive molecules, ultimately leading to the growth, stabilization, or regression of muscle capillaries. This remarkable plasticity of the capillary network is referred to as angio-adaptation. It can alter the capillary-to-myofiber interface, which represent an important determinant of skeletal muscle function. These angio-adaptive molecules can also be released in the circulation as myokines to act on distant tissues. This review addresses the respective and combined potency of ambient hypoxia and exercise to generate a cellular hypoxic stress in skeletal muscle. The major skeletal muscle angio-adaptive responses to hypoxia so far described in this context will be discussed, including existing controversies in the field. Finally, this review will highlight the molecular complexity of the skeletal muscle angio-adaptive response to hypoxia and identify current gaps of knowledges in this field of exercise and environmental physiology.

Affective and Enjoyment Responses to Sprint Interval Exercise at Different Hypoxia Levels

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.

Hypoxia, energy balance, and obesity: An update

Because of the enduring rise in the prevalence of obesity worldwide, there is continued interest in hypoxia as a mechanism underlying the pathophysiology of obesity and its comorbidities and as a potential therapeutic adjunct for the management of the disease. Lifelong exposure to altitude is accompanied by a lower risk for obesity, whereas altitude sojourns are generally associated with a loss of body mass. A negative energy balance upon exposure to hypoxia can be due to a combination of changes in determinants of energy expenditure (resting metabolic rate and physical activity energy expenditure) and energy intake (appetite). Over the past 15 years, the potential therapeutic interest of hypobaric or normobaric hypoxic exposure in individuals with obesity-to lower body mass and improve health status-has become an active field of research. Various protocols have been implemented, using actual altitude sojourns or intermittent normobaric hypoxic exposures, at rest or in association with physical activity. Although several studies suggest benefits on body mass and cardiovascular and metabolic variables, further investigations are required before recommending hypoxic exposure in obesity management programs. Future studies should also better clarify the effects of hypoxia on appetite, the intestinal microbiota, and finally on overall energy balance.

The Use of Artificial Hypoxia in Endurance Training in Patients after Myocardial Infarction

The presence of a well-developed collateral circulation in the area of the artery responsible for the infarction improves the prognosis of patients and leads to a smaller area of infarction. One of the factors influencing the formation of collateral circulation is hypoxia, which induces angiogenesis and arteriogenesis, which in turn cause the formation of new vessels. The aim of this study was to assess the effect of endurance training conducted under normobaric hypoxia in patients after myocardial infarction at the level of exercise tolerance and hemodynamic parameters of the left ventricle. Thirty-five patients aged 43–74 (60.48 ± 4.36) years who underwent angioplasty with stent implantation were examined. The program included 21 training units lasting about 90 min. A statistically significant improvement in exercise tolerance assessed with the cardiopulmonary exercise test (CPET) was observed: test duration (p < 0.001), distance covered (p < 0.001), HRmax (p = 0.039), maximal systolic blood pressure (SBPmax) (p = 0.044), peak minute ventilation (VE) (p = 0.004) and breathing frequency (BF) (p = 0.044). Favorable changes in left ventricular hemodynamic parameters were found for left ventricular end-diastolic dimension LVEDD (p = 0.002), left ventricular end-systolic dimension LVESD (p = 0.015), left ventricular ejection fraction (LVEF) (p = 0.021), lateral e’ (p < 0.001), septal e’ (p = 0.001), and E/A (p = 0.047). Endurance training conducted in hypoxic conditions has a positive effect on exercise tolerance and the hemodynamic indicators of the left ventricle.

Effects of Active and Passive Hypoxic Conditioning for 6 Weeks at Different Altitudes on Blood Lipids, Leptin, and Weight in Rats

Du, Xia, Olivier Girard, Rong yun Fan, and Fuhai Ma. Effects of active and passive hypoxic conditioning for 6 weeks at different altitudes on blood lipids, leptin, and weight in rats. High Alt Med Biol. 21:243-248, 2020. Objective: To compare the effects of 6 weeks of passive and active hypoxia exposure at different altitudes on lipid metabolism, leptin, and weight in rats. Materials and Methods: Eighty 9-week-old male Wistar rats were assigned to either non-exercise or exercise groups. Each group was subdivided into four categories (n = 10) based on hypoxic conditions: 0, 2200, 2200 + 3500, and 3500 m. Rats in the exercise group trained on a treadmill at a speed of 20-22 m/min (0° incline) for 90 minutes, 5 days per week for 6 weeks. Serum lipid and leptin levels and weight were measured following the intervention. Results: Total cholesterol (-8.2% ± 3.5%), low-density lipoproteins (-29.8% ± 8.1%), and triglyceride (TG) levels (-17.2% ± 3.8%) were lower, and high-density lipoproteins (+7.4% ± 4.0%) higher, in exercise versus non-exercise groups (all p < 0.001), independent of condition. TG levels were lower at altitude (-13.0% ± 27.3%, -10.9% ± 24.3%, and -9.2% ± 20.9% at 2200, 2200 + 3500, and 3500 m, respectively) compared to 0 m (p < 0.001). Hypoxic exposure decreased leptin with lower values at 2200 + 3500 m and 3500 m compared to 0 m (p < 0.05). Weight was lower in exercise than non-exercise groups (-8.2% ± 21.0%; p < 0.001), and at altitude (-2.7% ± 2.6%, -5.5% ± 3.7%, and -5.7% ± 2.7% at 2200, 2200 + 3500, and 3500 m, respectively) compared to 0 m. Conclusion: Regular aerobic exercise led to more favorable responses for lipid metabolism and weight control than the oxygenation conditions the animals are in.

Effects of Living High-Training Low and High on Body Composition and Metabolic Risk Markers in Overweight and Obese Females

This study examined the effects of 4 weeks of living high-training low and high (LHTLH) under moderate hypoxia on body weight, body composition, and metabolic risk markers of overweight and obese females. Nineteen healthy overweight or obese females participated in this study. Participants were assigned to the normoxic training group (NG) or the LHTLH group (HG). The NG participants lived and trained at sea level. The HG participants stayed for approximately 10 hours in a simulated 2300 m normobaric state of hypoxia for six days a week and trained for 2 hours 3 times a week under the same simulated hypoxia. The interventions lasted for 4 weeks. All groups underwent dietary restriction based on resting metabolic rate. The heart rate of the participants was monitored every ten minutes during exercise to ensure that the intensity was in the aerobic range. Compared with the preintervention values, body weight decreased significantly in both the NG and the HG (−8.81 ± 2.09% and −9.09 ± 1.15%, respectively). The fat mass of the arm, leg, trunk, and whole body showed significant reductions in both the NG and the HG, but no significant interaction effect was observed. The percentage of lean soft tissue mass loss in the total body weight loss tended to be lower in the HG (27.61% versus 15.94%, P=0.085). Between the NG and the HG, significant interaction effects of serum total cholesterol (−12.66 ± 9.09% versus −0.05 ± 13.36%,) and apolipoprotein A₁ (−13.66 ± 3.61% versus −5.32 ± 11.07%, P=0.042) were observed. A slight increase in serum high-density lipoprotein cholesterol (HDL-C) was observed in the HG (1.12 ± 12.34%) but a decrease was observed in the NG (−11.36 ± 18.91%). The interaction effect of HDL-C between NG and HG exhibited a significant trend (P=0.055). No added effects on serum triglycerides (TGs), low-density lipoprotein cholesterol (LDL-C), or APO-B were observed after 4 weeks of LHTLH. In conclusion, 4 weeks of LHTLH combined with dietary restriction could effectively reduce the body weight and body fat mass of overweight and obese females. Compared with training and sleeping under normoxia, no additive benefit of LHTLH on the loss of body weight and body fat mass was exhibited. However, LHTLH may help to relieve the loss of lean soft tissue mass and serum HDL-C.

Additive stress of normobaric hypoxic conditioning to improve body mass loss and cardiometabolic markers in individuals with overweight or obesity: A systematic review and meta-analysis

We performed a systematic review and meta-analysis to determine if hypoxic conditioning, compared to similar training near sea level, maximizes body mass loss and further improves cardiometabolic markers in overweight and obese individuals. A systematic search of PubMed, Web of Science and the Cochrane Library databases (up to January 2019) was performed. This analysis included randomized controlled trials with humans with overweight or obesity assessing the effects of HC on body mass loss or cardiometabolic markers. A subgroup analysis was performed to examine if HC effects differed between individuals with overweight or obesity. 13 articles (336 participants) qualified for inclusion. HC significantly decreased body mass (p = .01), fat mass (p = .04), waist/hip ratio (p < .001), waist (p < .001), LDL (p = .01), diastolic (p < .01) and systolic blood pressure (p < .01) with these effects not being larger than equivalent normoxic interventions. There were trends towards higher triglycerides decrement (p = .06) and higher muscle mass gain in hypoxic (p = .08) compared with normoxic condition. Also, the two BMI categories displayed no difference in the magnitude of the responses. Compared to normoxic equivalent, HC provides greater reductions in triglycerides and greater muscle growth, while body mass changes are similar. In addition, HC responses were essentially similar between individuals with overweight or obesity.

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.

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.

Detraining effect on overweight/obese women after high-intensity interval training in hypoxia

PURPOSE

Promising benefits on fat mass and biochemical components may be reported after applying programs of cyclic hypoxia and HIIT.

AIM

To investigate the effect of a month of detraining on cardiometabolic risk markers after active hypoxia exposure.

METHODS

Participants included 59 overweight/obese women, who started a 12-week program of 36 sessions, and were randomly divided into four groups: (a) aerobic interval training in hypoxia (AitH; FiO₂  = 17.2%; n = 13), (b) aerobic interval training in normoxia (AitN; n = 15), (c) sprint interval training in hypoxia (SitH; FiO₂  = 17.2%; n = 15), and (d) sprint interval training in normoxia (SitN; n = 18). Body composition, anthropometric, and biochemical parameters were assessed at baseline (A), after 36 training sessions (B) and after 4 weeks of detraining (C).

RESULTS

Hypoxia conditions showed a significant positive effect on waist circumference (P = 0.01), WHR (P = 0.04), and percentage of trunk fat mass (P < 0.001). The percentage of trunk fat continued to decrease significantly after training cessation in both AitH and SitH groups.

CONCLUSION

After 4 weeks of detraining with a previous 12 weeks of high-intensity interval training under cyclic normobaric hypoxia, the percentage of fat mass located in the trunk decreases significantly and this effect was not observed in the normoxia groups.

Effects of High-Intensity Interval Training Under Normobaric Hypoxia on Cardiometabolic Risk Markers in Overweight/Obese Women

Promising benefits on cardiometabolic risk factors have been reported with prolonged programs of cyclic hypoxia. The aim of this study was to examine whether cyclic hypoxia exposure while exercising through two protocols of high-intensity interval training in overweight/obese women is more effective to improve cardiometabolic risk markers than exercising in normoxia. Participants included 86 overweight/obese women, who started a 12-week program of 36 sessions, and were randomly divided into four groups: (1) interval training in hypoxia (IHT; FIO₂ = 17.2%; n = 13), (2) interval training in normoxia (INT; n = 15), which included 3-minute high-intensity exercise (90% Wmax) followed by 3 minutes of active recovery (55%-65% Wmax), (3) repeated-sprint training in hypoxia (RSH; FIO₂ = 17.2%; n = 15), and (4) repeated-sprint training in normoxia (RSN; n = 18), which included 30 seconds of all-out effort (130% Wmax) followed by 3 minutes of active recovery (55%-65% Wmax). Body composition, anthropometric, biochemical, and clinical parameters were assessed at baseline (A), after 18 training sessions (B), and during the 7 days after the last session (C). IHT and RSH showed a significant (p < 0.001 and p = 0.016, respectively) decrease in the waist circumference at both B and C assessments compared with A. Hypoxia groups presented a significant reduction in the percentage of trunk fat with a moderate effect size (IHT: d = 0.56; RSH: d = 0.93). In the normoxia groups, total cholesterol (CHOL) tended to decrease (INT: -4.21% and RSN: -5.18%), whereas it tended to increase in the hypoxia groups (IHT: +2.91% and RSH +4.07%). An interaction effect between conditions (through pooled data) on waist circumference (p = 0.01), percentage of trunk fat mass (p < 0.001), and CHOL (p = 0.019) was observed. Both training regimens under normobaric cyclic hypoxia were more effective at causing decreased abdominal fat in overweight/obese women than the same protocols in normoxia.

Endurance Training in Normobaric Hypoxia Imposes Less Physical Stress for Geriatric Rehabilitation

Rationale: Evidence suggests that training in hypoxia can be very effective even while requiring less physical effort. We therefore aimed to measure the effect of endurance training under hypoxic conditions on pulmonary and cardiovascular parameters in an elderly population undergoing inpatient rehabilitation. Methods: Forty patients over age 65 years with multiple co-morbid conditions were recruited during a 3-week stay in a geriatric rehabilitation center. Using a randomized, single-blinded, placebo-controlled design, patients were assigned to a hypoxic (HG) or normoxic (NG) group. HG patients completed seven training sessions of 30 min duration on a treadmill in a normobaric chamber with inspired oxygen fraction (FiO2) of 15.27%, with 10-30 min active training. Training was conducted with target heart rate at 80% of peak oxygen consumption (VO2-peak). NG group performed similar training in sham hypoxia (room air or FiO2 = 20.94%). At pre- and post-test completion, measures included: (1) cycle ergometry with ECG monitoring and measurement of VO2-peak, and (2) echocardiography for ejection fraction. Results: The physical effort required of patients to reach target heart rate was reduced significantly (-28%, p = 0.043) in the HG compared to NG. Cardiopulmonary parameters showed no differences between groups. Conclusion: Endurance training at 3,000 meters elevation imposes less stress on the locomotor systems while resulting in a similar physiological strain (i.e., heart rate). Hypoxic training holds promise for successful geriatric rehabilitation by being more accommodating to physical limitations in geriatric patients. Trial registration: Registration at DRKS. (Approval No. 359/12, Trial No. DRKS00005241).