Diaphragmatic, thoracic and abdominal breathing for sport: the effect on vagal activity, a case report

Breathing is important for any sport, particularly in aquatic sports. The autonomous response to diving is characterized by bradycardia mediated by the vagus nerve. Specific breathing techniques, particularly those involving deep and slow respiration tasks, could phasically and tonically stimulate the vagus nerve. This case report aimed to measure the effects of different breathing techniques (thoracic, diaphragmatic and spontaneous breathing) on autonomic vagal activity through simultaneous monitoring of ECG and ventilatory and thoraco-abdominal patterns. An elite male apneist was enrolled (50 years old, 186 cm, 80 kg) during spontaneous breathing (SB), diaphragmatic breathing (DB); thoracic breathing (TB) and diaphragmatic breathing combined with transverse abdominis activation (DTB) following a visual and acoustic timer to uniform the respiratory frequency at 6 breaths/minute. Compared to baseline, breathing exercises involving diaphragmatic recruitment (DB and DTB) increased the total power (index of overall autonomic activity and the plasticity of the cardiovascular system) by fourfold, while maintaining the mean heart rate nearly unchanged. However, the end-expiratory abdominal volume reduced during DB and DTB indicating a strong recruitment of the abdominal muscles. These results suggest that slow, deep and abdominal (and not just diaphragmatic) breathing enhanced vagal activity, independently of respiratory rate. We can speculate that a possible vagal stimulation occurs even when the diaphragm is stretched passively by the abdominal muscles. This mechanism would explain the vagal-related beneficial effects during exercise even in the absence of a direct increased diaphragmatic contribution. This hypothesis needs to be confirmed in a wider population.