Mechanisms underlying the health benefits of intermittent hypoxia conditioning.

Intermittent hypoxia (IH) is commonly associated with pathological conditions, particularly obstructive sleep apnoea. However, IH is also increasingly used to enhance health and performance and is emerging as a potent non-pharmacological intervention against numerous diseases. Whether IH is detrimental or beneficial for health is largely determined by the intensity, duration, number and frequency of the hypoxic exposures and by the specific responses they engender. Adaptive responses to hypoxia protect from future hypoxic or ischaemic insults, improve cellular resilience and functions, and boost mental and physical performance. The cellular and systemic mechanisms producing these benefits are highly complex, and the failure of different components can shift long-term adaptation to maladaptation and the development of pathologies. Rather than discussing in detail the well-characterized individual responses and adaptations to IH, we here aim to summarize and integrate hypoxia-activated mechanisms into a holistic picture of the body's adaptive responses to hypoxia and specifically IH, and demonstrate how these mechanisms might be mobilized for their health benefits while minimizing the risks of hypoxia exposure.

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) TH:RH, (b) TN:RH, (c) TN:RN, 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.

Effects of whole-body vibration under hypoxic exposure on muscle mass and functional mobility in older adults.

BACKGROUND: Ageing is accompanied by a loss of muscle mass and function, which are associated with decrease of functional capacity. Combination of WBV training with normobaric hypoxic exposure could augment the beneficial effects due to synergic effects of both treatments. AIMS: The purpose of this study was to examine the effects of 36 sessions of the combined WBV training and normobaric hypoxic exposure on muscle mass and functional mobility in older adults. METHODS: Nineteen elderly people were randomly assigned to a: vibration normoxic exposure group (NWBV; n = 10; 20.9% FiO2) and vibration hypoxic exposure group (HWBV; n = 9). Participants developed 36 sessions of WBV training along 18 weeks, which included 4 bouts of 30 s (12.6 Hz in frequency and 4 mm in amplitude) with 60 s of rest between bouts, inside a hypoxic chamber for the HWBV. The "Timed Up and Go Test" evaluated functional mobility. Percentages of lean mass were obtained with dual-energy X-ray absorptiometry. RESULTS: Neither statistically significant within group variations nor statistically significant differences between both groups were detected to any parameter. DISCUSSION: Baseline characteristics of population, training protocol and the level of hypoxia employed could cause different adaptations on muscle mass and function. CONCLUSIONS: The combination of WBV training and hypoxic exposure did not cause any effect on either legs lean mass or functional mobility of older adults.