Effects of dynamic apnea training on diving bradycardia and short distance swimming performance

Chemoreflex Control as the Cornerstone in Immersion Water Sports: Possible Role on Breath-Hold

Immersion water sports involve long-term apneas; therefore, athletes must physiologically adapt to maintain muscle oxygenation, despite not performing pulmonary ventilation. Breath-holding (i.e., apnea) is common in water sports, and it involves a decrease and increases PaO₂ and PaCO₂, respectively, as the primary signals that trigger the end of apnea. The principal physiological O₂ sensors are the carotid bodies, which are able to detect arterial gases and metabolic alterations before reaching the brain, which aids in adjusting the cardiorespiratory system. Moreover, the principal H⁺/CO₂ sensor is the retrotrapezoid nucleus, which is located at the brainstem level; this mechanism contributes to detecting respiratory and metabolic acidosis. Although these sensors have been characterized in pathophysiological states, current evidence shows a possible role for these mechanisms as physiological sensors during voluntary apnea. Divers and swimmer athletes have been found to displayed longer apnea times than land sports athletes, as well as decreased peripheral O₂ and central CO₂ chemoreflex control. However, although chemosensitivity at rest could be decreased, we recently found marked sympathoexcitation during maximum voluntary apnea in young swimmers, which could activate the spleen (which is a reservoir organ for oxygenated blood). Therefore, it is possible that the chemoreflex, autonomic function, and storage/delivery oxygen organ(s) are linked to apnea in immersion water sports. In this review, we summarized the available evidence related to chemoreflex control in immersion water sports. Subsequently, we propose a possible physiological mechanistic model that could contribute to providing new avenues for understanding the respiratory physiology of water sports.

Symptomatic second-degree atrioventricular block in a recreational athlete

This case study provides an example of bradycardia associated with an increase in exercise training in a recreational athlete. Although recognised among high-level endurance athletes, this case demonstrates the potential negative effects of exercise on the heart in a patient participating in the levels of exercise recommended by Public Health England. It adds weight to the ongoing discussion of the incomplete understanding of the level of exercise needed to induce pathological changes in cardiac physiology. We discuss the investigations that led us to our diagnosis, highlighting the importance of a detailed exercise history in patients who present with palpitations and provide a potential explanation of how this phenomenon may have occurred. Currently, bradycardia induced by exercise has been managed through pacemaker insertion or complete cessation of exercise. This report demonstrates effective treatment through a period of exercise cessation and slow reintroduction of exercise training.