About this Research Topic
Hypoxia is defined as a reduced/insufficient oxygen supply to tissues leading to decreased oxygen availability. Hypoxia can either be achieved naturally (hypobaric hypoxia) when traveling to terrestrial altitude, or artificially through hypoxic simulation (normobaric hypoxia), such as vascular occlusion-induced hypoxia or facecovering-induced hypoxia. Exposure to hypoxia induces a broad range of positive (performance gains, upregulated physiological systems) and negative (deleterious consequences, maladaptations) responses.
Accumulated evidence suggests that altitude/hypoxic training for several weeks can improve exercise performance when athletes train/compete at terrestrial altitude or after returning to sea level. While altitude training has been incorporated in the training periodization of many athletes for almost half a century, the last decade has seen the development of a large number of new hypoxic modalities. While performance-led investigations have mainly been conducted, our understanding of underpinning physiological (in particular molecular pathways) mechanisms driving these functional benefits is incomplete.
Passive hypoxic exposure may induce tissue specific adaptations, such as changes in ventilation, cerebral ischemia, myocardial ischemia, etc. Hypoxia also exerts whole-body systemic adaptations through complex signaling networks, such as changes in blood circulation, blood pressure, cytokines (small secreted proteins released by various types of cells) released from multiple tissues or organs. These adaptations have the potential to improve exercise tolerance both in athletic but also patient populations. To date, however, it remains unclear what is an appropriate dose (duration, severity, pattern) of hypoxic exposure to obtain larger positive effects.
Similar to hypoxia, exercise leads to adaptive responses in tissues directly involved in contractile activity, such as skeletal muscle and myocardial cells. Exercise also induces multisystemic functional adaptations in several tissues and organs via inter-organ crosstalk, likely mediated via myokines (factors released from skeletal muscle) and exerkines (factors released in response to exercise). At the systemic level, exercise training (chronic effects of several exercise sessions) likely induces positive changes in cellular metabolism, blood distribution in the body, thermoregulation, etc.
The combined effects of hypoxia and exercise have been explored by previous collections published in this journal, including one exploring it as a potential treatment for obesity, and another investigating benefits and potential drawbacks of high-intensity exercise in hypoxia. Given that this field is fast evolving and that our understanding of tissue-specific adaptations for improved hypoxic and/or exercise tolerance is still incomplete, this Research Topic represents a window of opportunity to gather new knowledge on some of the upregulated physiological pathways likely induced by these interventions. This Research Topic aims to shed more light on the tissue specific and multi-systemic adaptations to hypoxia, and the combination of hypoxia and exercise.
All formats of contributions (original research papers, opinions, full reviews, mini-reviews) will be considered. Basic research at the cellular or sub-cellular level, translational research using animal experiments and human physiological as well as epidemiological or interventional studies are welcome.
Keywords: Hypoxia, Exercise, Systemic adaptations, Tissue-specific adaptations
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