Physiology, pathophysiology and (mal)adaptations to chronic apnoeic training: a state-of-the-art review

Abstract

Breath-hold diving is an activity that humans have engaged in since antiquity to forage for resources, provide sustenance and to support military campaigns. In modern times, breath-hold diving continues to gain popularity and recognition as both a competitive and recreational sport. The continued progression of world records is somewhat remarkable, particularly given the extreme hypoxaemic and hypercapnic conditions, and hydrostatic pressures these athletes endure. However, there is abundant literature to suggest a large inter-individual variation in the apnoeic capabilities that is thus far not fully understood. In this review, we explore developments in apnoea physiology and delineate the traits and mechanisms that potentially underpin this variation. In addition, we sought to highlight the physiological (mal)adaptations associated with consistent breath-hold training. Breath-hold divers (BHDs) are evidenced to exhibit a more pronounced diving-response than non-divers, while elite BHDs (EBHDs) also display beneficial adaptations in both blood and skeletal muscle. Importantly, these physiological characteristics are documented to be primarily influenced by training-induced stimuli. BHDs are exposed to unique physiological and environmental stressors, and as such possess an ability to withstand acute cerebrovascular and neuronal strains. Whether these characteristics are also a result of training-induced adaptations or genetic predisposition is less certain. Although the long-term effects of regular breath-hold diving activity are yet to be holistically established, preliminary evidence has posed considerations for cognitive, neurological, renal and bone health in BHDs. These areas should be explored further in longitudinal studies to more confidently ascertain the long-term health implications of extreme breath-holding activity.

Effect of Apnea-Induced Hypoxia on Cardiovascular Adaptation and Circulating Biomarkers of Oxidative Stress in Elite Breath-Hold Divers

“…These results might indicate an increase in lung volume and function as an important factor in adapting the mechanism to freediving ( Overgaard et al, 2006 ). Several other adaptive mechanisms cannot be ruled out that protect against hypercapnia and hypoxemia developing during apnea ( Lindholm and Lundgren, 2008 ; Bain et al, 2018 ; Taboni et al, 2019 ; Elia et al, 2021 ).…”

“…Individual and team world freediving championships include disciplines, such as Static Apnea (STA) in which the diver holding his breath for as long as possible with his nose and mouth immersed, or Dynamic Apnea in which the diver travels underwater attempting to cover the greatest possible distance with or without fins ( Elia et al, 2021 ). The trends in improving world records in this sport indicate specific training protocol including endurance training and breath-hold training with hypoxia exposition ( Heusser et al, 2009 ; Cross et al, 2013 ).…”

Going to Extremes of Lung Physiology–Deep Breath-Hold Diving

“…Lastly, there are possible implications of the diving reflex in breath-hold diving narcosis. Apnea induces a reflex mechanism known as the diving reflex, which is mainly characterized by bradycardia and peripheral vasoconstriction that allows blood to be redirected to oxygen-dependent organs such as the heart and brain (Joulia et al, 2009;Lindholm and Lundgren, 2009;Dujic and Breskovic, 2012;Eichhorn et al, 2017;Bain et al, 2018;Elia et al, 2021). This mechanism is more or less present depending on the intensity of the effort, but it seems to be persistent during ascent of constant weight diving (Lemaître et al, 2013).…”

Cerebral, cardiac and skeletal muscle stress associated with a series of static and dynamic apnoeas

“…Breath‐hold diving continues to gain popularity and recognition as both a competitive and recreational sport. The continued progression of world records is astonishing, particularly given the extreme hypoxaemic hypercapnia and hydrostatic pressures these athletes endure; yet, the continued pursuit of performance raises safety concerns 1 . To date, a breadth of research exists that has delineated the physiological characteristics of breath‐hold divers, as well as the responses that occur during and/or following prolonged apnoeic bouts (e.g, the diving response, trigeminocardiac reflex, splenic contractions, erythropoietic responses, etc.)…”

“…To date, a breadth of research exists that has delineated the physiological characteristics of breath‐hold divers, as well as the responses that occur during and/or following prolonged apnoeic bouts (e.g, the diving response, trigeminocardiac reflex, splenic contractions, erythropoietic responses, etc.) 1‐8 . In contrast, there is a paucity of literature concerning the possible health implications associated with exposure to such activities 9‐14 …”