Hypoxia and exercise interactions on skeletal muscle insulin sensitivity in obese subjects with metabolic syndrome: results of a randomized controlled trial

The role of tissue oxygenation in obesity-related cardiometabolic complications

Obesity is a complex, multifactorial, chronic disease that acts as a gateway to a range of other diseases. Evidence from recent studies suggests that changes in oxygen availability in the microenvironment of metabolic organs may exert an important role in the development of obesity-related cardiometabolic complications. In this review, we will first discuss results from observational and controlled laboratory studies that examined the relationship between reduced oxygen availability and obesity-related metabolic derangements. Next, the effects of alterations in oxygen partial pressure (pO2) in the adipose tissue, skeletal muscle and the liver microenvironment on physiological processes in these key metabolic organs will be addressed, and how this might relate to cardiometabolic complications. Since many obesity-related chronic diseases, including type 2 diabetes mellitus, cardiovascular diseases, chronic kidney disease, chronic obstructive pulmonary disease and obstructive sleep apnea, are characterized by changes in pO2 in the tissue microenvironment, a better understanding of the metabolic impact of altered tissue oxygenation can provide valuable insights into the complex interplay between environmental and biological factors involved in the pathophysiology of metabolic impairments. This may ultimately contribute to the development of novel strategies to prevent and treat obesity-related cardiometabolic diseases.

Anaerobic threshold using sweat lactate sensor under hypoxia

We aimed to investigate the reliability and validity of sweat lactate threshold (sLT) measurement based on the real-time monitoring of the transition in sweat lactate levels (sLA) under hypoxic exercise. In this cross-sectional study, 20 healthy participants who underwent exercise tests using respiratory gas analysis under hypoxia (fraction of inspired oxygen [FiO2], 15.4 ± 0.8%) in addition to normoxia (FiO2, 20.9%) were included; we simultaneously monitored sLA transition using a wearable lactate sensor. The initial significant elevation in sLA over the baseline was defined as sLT. Under hypoxia, real-time dynamic changes in sLA were successfully visualized, including a rapid, continual rise until volitionary exhaustion and a progressive reduction in the recovery phase. High intra- and inter-evaluator reliability was demonstrated for sLT's repeat determinations (0.782 [0.607-0.898] and 0.933 [0.841-0.973]) as intraclass correlation coefficients [95% confidence interval]. sLT correlated with ventilatory threshold (VT) (r = 0.70, p < 0.01). A strong agreement was found in the Bland-Altman plot (mean difference/mean average time: - 15.5/550.8 s) under hypoxia. Our wearable device enabled continuous and real-time lactate assessment in sweat under hypoxic conditions in healthy participants with high reliability and validity, providing additional information to detect anaerobic thresholds in hypoxic conditions.

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.

The Influence of COVID-19 in Endocrine Research: Critical Overview, Methodological Implications and a Guideline for Future Designs

The COVID-19 pandemic has changed many aspects of people's lives, including not only individual social behavior, healthcare procedures, and altered physiological and pathophysiological responses. As a result, some medical studies may be influenced by one or more hidden factors brought about by the COVID-19 pandemic. Using the literature review method, we are briefly discussing the studies that are confounded by COVID-19 and facemask-induced partiality and how these factors can be further complicated with other confounding variables. Facemask wearing has been reported to produce partiality in studies of ophthalmology (particularly dry eye and related ocular diseases), sleep studies, cognitive studies (such as emotion-recognition accuracy research, etc.), and gender-influenced studies, to mention a few. There is a possibility that some other COVID-19 related influences remain unrecognized in medical research. To account for heterogeneity, current and future studies need to consider the severity of the initial illness (such as diabetes, other endocrine disorders), and COVID-19 infection, the timing of analysis, or the presence of a control group. Face mask-induced influences may confound the results of diabetes studies in many ways.

Combined Aerobic and Resistance Training Performed under Conditions of Normobaric Hypoxia and Normoxia Has the Same Impact on Metabolic Control in Men with Type 1 Diabetes

(1) Background: The aim was to assess whether combined aerobic and resistance training performed under hypoxic and normoxic conditions had an impact on diabetes control, VO2max (maximum oxygen consumption), and echocardiological and anthropometric parameters in men with long-term type 1 diabetes. (2) Methods: Sixteen male participants (mean age: 37 years, mean HbA1c (glycated hemoglobin): 7.0%) were randomly assigned to two groups: training in normoxic conditions or training in conditions of altitude hypoxia. All subjects participated in 60 min combined aerobic and resistance training sessions twice a week for 6 weeks. At baseline and in the 6th week, echocardiography, incremental exercise test, and anthropometric and diabetes control parameters were assessed. (3) Results: After 6 weeks, there was no significant change in HbA1c value in any group. We noted a more stable glycemia profile during training in the hypoxia group (p > 0.05). Patients in the hypoxia group required less carbohydrates during training than in the normoxia group. A comparable increase in VO2max was observed in both groups (p > 0.05). There were no significant differences in cardiological and anthropometric parameters. (4) Conclusions: Combined aerobic and resistance training improved VO2max after 6 weeks regardless of the conditions of the experiments. This exercise is safe in terms of glycemic control in patients with well-controlled diabetes.

Hypoxic Exercise Exacerbates Hypoxemia and Acute Mountain Sickness in Obesity: A Case Analysis

Acute mountain sickness (AMS) is a common syndrome characterized by headache, dizziness, loss of appetite, weakness, and nausea. As a major public health issue, obesity has increased in high altitude urban residents and intermittent commuters to high altitudes. The present study investigated acute hypoxic exposure and hypoxic exercise on hypoxemia severity and AMS symptoms in a physically active obese man. In this case analysis, peripheral oxygen saturation (SpO₂) was used to evaluate hypoxemia, heart rate (HR) and blood pressure (BP) were used to reflect the function of autonomic nervous system (ANS), and Lake Louise scoring (LLS) was used to assess AMS. The results showed that acute hypoxic exposure led to severe hypoxemia (SpO₂ = 72%) and tachycardia (HRrest = 97 bpm), and acute hypoxic exercise exacerbated severe hypoxemia (SpO₂ = 59%) and ANS dysfunction (HRpeak = 167 bpm, SBP/DBP = 210/97 mmHg). At the end of the 6-h acute hypoxic exposure, the case developed severe AMS (LLS = 10) symptoms of headache, gastrointestinal distress, cyanosis, vomiting, poor appetite, and fatigue. The findings of the case study suggest that high physical activity level appears did not show a reliable protective effect against severe hypoxemia, ANS dysfunction, and severe AMS symptoms in acute hypoxia exposure and hypoxia exercise.

Post-exercise cardiac autonomic and cardiovascular responses to heart rate-matched and work rate-matched hypoxic exercise

Purpose

This study investigated the effect of performing hypoxic exercise at the same heart rate (HR) or work rate (WR) as normoxic exercise on post-exercise autonomic and cardiovascular responses.

Methods

Thirteen men performed three interval-type exercise sessions (5 × 5-min; 1-min recovery): normoxic exercise at 80% of the WR at the first ventilatory threshold (N), hypoxic exercise (FiO₂ = 14.2%) at the same WR as N (H-WR) and hypoxic exercise at the same HR as N (H-HR). Autonomic and cardiovascular assessments were conducted before and after exercise, both at rest and during active squat–stand manoeuvres (SS).

Results

Compared to N, H-WR elicited a higher HR response (≈ 83% vs ≈ 75%HRmax, p < 0.001) and H-HR a reduced exercise WR (− 21.1 ± 9.3%, p < 0.001). Cardiac parasympathetic indices were reduced 15 min after exercise and recovered within 60 min in N and H-HR, but not after H-WR (p < 0.05). H-WR altered cardiac baroreflex sensitivity (cBRS) both at rest and during SS (specifically in the control of blood pressure fall during standing phases) in the first 60 min after the exercise bout (p < 0.05). Post-exercise hypotension (PEH) did not occur in H-HR (p > 0.05) but lasted longer in H-WR than in N (p < 0.05).

Conclusions

Moderate HR-matched hypoxic exercise mimicked post-exercise autonomic responses of normoxic exercise without resulting in significant PEH. This may relate to the reduced WR and the limited associated mechanical/metabolic strain. Conversely, WR-matched hypoxic exercise impacted upon post-exercise autonomic and cardiovascular responses, delaying cardiac autonomic recovery, temporarily decreasing cBRS and evoking prolonged PEH.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00421-021-04678-5.

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.