Physiology

The mammalian dive reflex

Submerge your face and your body does something ancient: the heart slows, the blood vessels in your limbs clamp down, and blood shifts into your chest. It's the same reflex seals and dolphins run on.

bradycardia        heart rate drops 10–25%
vasoconstriction   the limbs clamp down
blood shift        protects the lungs at depth
spleen release     adds oxygenated red cells

Why it matters

The reflex is your free performance. The more relaxed you are, the stronger it fires. Tension fights it.