Freediving turns the absence of breath into a survival skill and a sport. Ancient Greek sponge divers rode a skandalopetra stone of up to 15 kilograms to depths of about 30 meters and were hauled back by a partner. In the Peloponnesian War, divers slipped under blockades to carry messages and supplies, and at the Siege of Tyre in 332 BC they cut the anchor cables of Alexander the Great’s ships. Japan’s Ama, traditionally women, have gathered pearls for some 2,000 years, and in the Sulu Archipelago the largest pearls belonged to the Sultan by law, with death for secret sales. Dottie Frazier broke barriers for women in the 1940s and designed rubber suits for Navy divers.

Cold water on the face triggers the mammalian dive reflex, slowing the heart and pulling blood to the brain and heart, and the spleen squeezes out stored red blood cells. The Bajau sea nomads of Southeast Asia have evolved genetically larger spleens. The urge to breathe comes from rising carbon dioxide, not falling oxygen, so hyperventilating before a dive silences the alarm while oxygen keeps dropping, inviting a blackout with no warning. On ascent, expanding lung gas drops oxygen pressure and can pull oxygen from the brain. Competitive apnea under AIDA and CMAS pits athletes against time and depth.

• Stephane Mifsud holds an AIDA static apnea record of 11 minutes 35 seconds.
• In constant weight, Alexey Molchanov reached 133 meters and Alessia Zecchini 123 meters.
• Herbert Nitsch rode a sled to 214 meters in No Limits, a discipline AIDA no longer recognizes.
• Safety divers meet athletes at a third to a quarter of target depth and seal the airway of anyone who blacks out.
• Aquathlon, underwater wrestling from the 1980s USSR, and underwater hockey, invented by Alan Blake in England in 1954, test breath-hold under exertion.