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

The Impact of Exercise Training in a Hypobaric/Normobaric Hypoxic Environment on Cardiometabolic Health in Adults with Overweight or Obesity: A Systematic Review and Meta-Analysis

This systematic review and meta-analysis aims to comprehensively evaluate the effects of hypoxic training (HT) versus normoxic training (NT) on cardiometabolic health parameters in overweight or obese adults. Searches were performed in PubMed, Web of Science, Embase, Scopus, and the Cochrane Library. A meta-analysis was performed using Stata 18 and RevMan 5.4 software. Seventeen randomized controlled studies involving 517 participants were included. HT significantly improved cardiorespiratory fitness (CRF) and reduced systolic blood pressure (SBP) and diastolic blood pressure (DBP). Compared with NT, HT demonstrated a significant difference in CRF, but no significant differences were observed in SBP and DBP. The subgroup analysis of CRF revealed that HT significantly outperformed NT in six aspects: participants aged < 45 years (Hedges' g = 0.50), an intervention duration of 8 weeks (Hedges' g = 0.43), three sessions per week (Hedges' g = 0.40), each session lasting < 45 min (Hedges' g = 0.23), FiO2 levels > 15% (Hedges' g = 0.69), and high-load-intensity exercise (Hedges' g = 0.57). HT demonstrated favorable effects in improving cardiometabolic health among overweight or obese adults. Compared with NT, this advantage was primarily reflected in CRF while the impacts on SBP and DBP were similar.

Impact of exercise training in a hypobaric/normobaric hypoxic environment on body composition and glycolipid metabolism in individuals with overweight or obesity: a systematic review and meta-analysis

Objective

This study aims to assess the impact of hypoxia training on body composition and glycolipid metabolism in excess body weight or living with obese people through meta-analysis.

Methods

Randomized controlled trials investigating the effects of hypoxia training on body composition, glucose, and lipid metabolism in excess body weight or living with obese people were systematically searched from databases including CNKI, PubMed, and Web of Science. The meta-analysis was performed by using Stata 18 and RevMan 5.4 analytic tools. The risk of bias was assessed using the Cochrane evaluation tool, and the level of certainty of evidence was determined by the GRADE framework. Between-study heterogeneity was examined using the I 2 test, and the publication bias was evaluated via the Egger test or funnel plot.

Results

A total of 32 RCTs with 1,011 participants were included. A meta-analysis of 25 RCTs was performed (499 men and 480 women, Age: 40.25 ± 15.69, BMI: 30.96 ± 3.65). In terms of body composition, the outcome indexes of body fat ratio (MD is -1.16, 95% CI -1.76 to -0.56, P = 0.00) in the hypoxia group were better than the normal oxygen group. There was no significant difference in body mass and BMI between the hypoxia group and the normal-oxygen group (P > 0.05). In terms of lipid and glucose metabolism, no significant changes were found between the hypoxia group and the normoxia group (P > 0.05). Subgroup analysis showed that training in hypoxic environment at altitude 2001-2,500 m could effectively improve body mass, TG and LDL-C (P < 0.05). The effective program to reduce body mass is to carry out moderate intensity training of 45-60 min for ≤8 weeks, ≥4 times a week (P < 0.05).

Conclusion

Hypoxic training is essential for reducing body fat ratio in excess body weight or obese people. It is recommended to carry out 45-60 min of moderate-intensity aerobic exercise for ≤8 weeks, ≥4 times a week, in a hypoxia environment of 2,001-2,500 m to lose body mass. The effects of hypoxia training and normoxia training on lipid and glucose metabolism in excess body weight or obese people are the same.

Systematic Review Registration

https://www.crd.york.ac.uk/PROSPERO/view/CRD42024628550.

Intermittent Hypoxic Training Increases and Prolongs Exercise Benefits in Adult Untrained Women

Camacho-Cardenosa, Alba, Marta Camacho-Cardenosa, Johannes Burtscher, Pedro R. Olivares, Guillermo Olcina, and Javier Brazo-Sayavera. Intermittent hypoxic training increases and prolongs exercise benefits in adult untrained women. High Alt Med Biol. 25:274-284, 2024. Background: Exercising in hypoxia may confer multiple health benefits, but the evidence for specific benefits is scarce. Methods: We investigated effects of intermittent hypoxic training (IHT) on the quality of life and functional fitness of healthy adult women, in a double-blind, randomized, placebo-controlled study. Subjects performed 36 sessions of IHT (experimental group, n = 41; fraction of inspired oxygen [FIO2]: 0.17) or the same training in normoxia (control group, n = 41; FIO2: 0.21). Health-related quality of life, fitness tests, and hemoglobin levels were assessed before (T1), directly after (T2), and 4 weeks after (T3) cessation. Results: At T2, upper body strength (+14.96%), lower body strength (+26.20%), and agility (-4.94%) increased significantly in the experimental group compared to baseline but not in controls. The experimental group improved lower body strength more (by 9.85%) than controls at T2 and performed significantly better in walking (by 2.92%) and upper body strength testing (by 16.03%), and agility (by 4.54%) at T3. Perceived general health and vitality was significantly greater in the experimental group at T2 and T3 compared with T1. None of these improvements were observed in the control group. Conclusions: IHT is a promising strategy to induce long-lasting fitness benefits in healthy adult women.

Discontinuation of HIIT restores diabesity while retraining increases gut microbiota diversity

Investigations involving high-intensity interval training (HIIT) have proven to be efficient in controlling diabesity. This study aimed to assess the impact of discontinuing HIIT and retraining within the context of diabesity. 75 C57BL6 mice went through 5 stages: baseline, induction of diabesity with Western diet, training, detraining, and retraining (6 weeks each period). Detraining led to elevated adiposity, exacerbated metabolic parameters and intestinal health, and altered gut microbiota composition. Retraining restored blood glucose regulation and enhanced intestinal health yet did not induce fat reduction. While both training and retraining exerted an effect on the composition of the gut microbiota, the impact of diet demonstrates a more substantial potency compared to that of exercise concerning intestinal health and microbiome. These findings may contribute to a broader understanding of diabesity management and introduce perspectives for the use of specific physical training to enhance patient outcomes and intestine health.

miR-122/PPARβ axis is involved in hypoxic exercise and modulates fatty acid metabolism in skeletal muscle of obese rats

Hypoxic exercise is an effective intervention for obesity, because it promotes weight loss by regulating fatty acid (FA) metabolism. The regulation of peroxisome proliferator-activated receptor β (PPARβ) by miR-122 may be involved in this process, but the detailed mechanisms are unknown. In order to address this issue, we probed how miR-122 affected the expression of factors associated with FA metabolism in skeletal muscle of obese rats undergoing hypoxic training. By injecting adeno-associated virus 9 containing miR-122 overexpression vector or miR-122 inhibitor into skeletal muscles of rats with a 4-week hypoxic exercise regimen, the miR-122 expression level can be regulated. Body composition and blood lipid levels were analyzed, and PPARβ, carnitine palmitoyltransferase 1b (CPT1b), acetylCoA carboxylase 2 (ACC2), and FA synthase (FAS) mRNA and protein levels were evaluated using quantitative reverse transcription quantitative PCR(RT-qPCR) and Western blot analysis. We found that miR-122 overexpression increased low-density lipoprotein cholesterol (LDL-C) and triglyceride (TG) levels and decreased PPARβ, ACC2, and FAS expression. Conversely, miR-122 inhibition decreased TG level, increased high-density lipoprotein cholesterol (HDL-C) level, and upregulated PPARβ, ACC2, FAS, and CPT1b. These data indicated that the negative regulation of PPARβ by miR-122 promotes FA metabolism by altering the levels of the factors related to FA metabolism in skeletal muscle of obese rat under hypoxic training, thus providing molecular-level insight into the beneficial effects of this intervention.

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.

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.

Effects of moderate-intensity intermittent hypoxic training on health outcomes of patients recovered from COVID-19: the AEROBICOVID study protocol for a randomized controlled trial

Background

Recent studies point to a lower number and reduced severity of cases in higher altitude cities with decreased oxygen concentration. Specific literature has shown several benefits of physical training, so, in this sense, physical training with hypoxic stimulus appears as an alternative that supports the conventional treatments of the COVID-19 patient’s recovery. Thus, this study’s primary aim is to analyze the effects of moderate-intensity intermittent hypoxic training on health outcomes in COVID-19 recovered patients.

Methods

A clinical trial controlled double-blind study was designed. Participants (30–69 years old) will be recruited among those with moderate to severe COVID-19 symptoms, approximately 30 days after recovery. They will be included in groups according to the training (T) and recovery (R) association with hypoxia (H) or normoxia (N): (a) T_H:R_H, (b) T_N:R_H, (c) T_N:R_N, and last (d) the control group. The 8-week exercise bike intervention will be carried out with a gradual load increase according to the established periods, three times a week in sets of 5 min, 90 to 100% of the anaerobic threshold (AT), and a 2.5-min break. Blood will be collected for genotyping. First, after 4 weeks (partial), after 8 weeks, and later, 4 weeks after the end of the physical training intervention, participants will perform assessments. The primary outcome is the maximum oxygen consumption (VO₂peak). The secondary outcomes include lung function, inflammatory mediators, hematological, autonomic parameters, AT, body composition analysis, quality of life, mental health, anthropometric measurements, and physical fitness. The statistical analysis will be executed using the linear regression model with mixed effects at a 5% significance level.

Discussion

This study is designed to provide evidence to support the clinical benefits of moderate-intensity intermittent hypoxic training as a part of the treatment of patients recovered from COVID-19. It may also provide evidence on the efficacy and safety of intermittent hypoxic training in different health conditions. Lastly, this study presents an innovative strategy enabling up to 16 participants in the same training session.

Trial registration

ClinicalTrials.gov RBR-5d7hkv. Registered after the start of inclusion on 3 November 2020 with the Brazilian Clinical Trials Registry

Supplementary Information

The online version contains supplementary material available at 10.1186/s13063-021-05414-2.

Is Physical Exercise in Hypoxia an Interesting Strategy to Prevent the Development of Type 2 Diabetes? A Narrative Review

Impaired metabolism is becoming one of the main causes of mortality and the identification of strategies to cure those diseases is a major public health concern. A number of therapies are being developed to treat type 2 diabetes mellitus (T2DM), but few of them focus on situations prior to diabetes. Obesity, aging and insulin resistance are all risk factors, which fortunately can be reversed to some extent. Non-drug interventions, such as exercise, are interesting strategies to prevent the onset of diabetes, but it remains to determine the optimal dose and conditions. In the search of optimizing the effects of physical exercise to prevent T2DM, hypoxic training has emerged as an interesting and original strategy. Several recent studies have chosen to look at the effects of hypoxic training in people at risk of developing T2DM. Therefore, the purpose of this narrative review is to give an overview of all original articles having tested the effects of a single exercise or exercise training in hypoxia on glucose metabolism and other health-related parameters in people at risk of developing T2DM. Taken together, the data on the effects of hypoxic training on glucose metabolism, insulin sensitivity and the health status of people at risk of T2DM are inconclusive. Some studies show that hypoxic training can improve glucose metabolism and the health status to a greater extent than normoxic training, while others do not corroborate the latter. When an additional benefit of hypoxic vs normoxic training is found, it still remains to determine which signaling pathways and molecular mechanisms are involved.

Inhibition of miR-27b Regulates Lipid Metabolism in Skeletal Muscle of Obese Rats During Hypoxic Exercise by Increasing PPARγ Expression

Hypoxic exercise may represent a novel therapeutic strategy to reduce and prevent obesity through the regulation of lipid metabolism. During hypoxic exercise, the targeting of peroxisome proliferator-activated receptor gamma (PPARγ) by miR-27b has been proposed to be one of the mechanisms involved in the modulation of lipid metabolism. We have previously shown that miR-27b can repress PPARγ and lipid metabolism-associated factors, thereby affecting lipid metabolism during hypoxic exercise in a rat model of obesity. In the current study, we aimed to confirm the role of miR-27b in the regulation of lipid metabolism. First, miR-27b expression was either upregulated or downregulated through the injection of adeno-associated virus (AAV) 9 containing a miR-27b expression cassette or miR-27b-3p inhibitor, respectively, into the right gastrocnemius muscle of obese rats. The rats were then subjected to a 4-week program of hypoxic exercise, and a series of parameters related to lipid metabolism were systematically evaluated, including body composition, blood lipid levels, miR-27b RNA levels, and mRNA and protein levels of PPARγ and those of its downstream lipid metabolism-associated factors. No significant differences were found in body composition between rats expressing different levels of miR-27b. However, regarding blood lipids, miR-27b overexpression led to increased concentrations of triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), and free fatty acids (FFAs), while inhibition of miR-27b decreased the total cholesterol (TC) level and increased that of high-density lipoprotein cholesterol (HDL-C). At the mRNA level, miR-27b overexpression downregulated the expression of Pparγ, but upregulated that of lipid metabolism-associated factors such as heart-type fatty acid-binding protein (H-FABP), fatty acid transport protein 1 (FATP1), adipose triglyceride lipase (ATGL), and lipoprotein lipase (LPL), whereas miR-27b inhibition elicited the opposite effect; however, inhibition of miR-27b led to elevated cholesterol 7 alpha-hydroxylase (CYP7A1) and fatty acid translocase 36 (CD36) levels. Similarly, at the protein level, miR-27b overexpression promoted a decrease in the concentration of PPARγ, whereas miR-27b inhibition led to an increase in PPARγ levels, as well as those of CYP7A1, CD36, ATGL, and LPL. Overall, our results indicated that hypoxic exercise regulates lipid metabolism via the miR-27b/PPARγ pathway and modulates ATGL and LPL expression through inducing their post-transcriptional modifications.