Breath‑Hold Diving Training for Cardiovascular Plasticity and Spleen Enlargement
Ilardo’s work distinguishes between the acute dive reflex (present in everyone) and chronic training adaptations. The Haenyeo, who have dived nearly daily for decades, exhibit far deeper heart‑rate drops. This lifelong conditioning is an example of how extreme environmental demands reshape autonomic responses. Separately, controlled experiments in non‑diving populations have shown that weeks of breath‑hold training can enlarge the spleen, indicating a plastic component that may complement genetic advantages.
Repeated apnea and cold‑face immersion progressively enhance vagal tone, leading to deeper bradycardia. Enhanced catecholamine or other signals likely stimulate splenic smooth muscle adaptation, increasing storage capacity. The Haenyeo’s extreme bradycardia appears to be a training effect, as it is absent in non‑diving relatives with the same genetics.
Their heart rate through a lifetime of training slows down even more. … We had one individual whose heart rate dropped more than 40 beats per minute in less than 15 seconds.