On November 23, 1976, off the island of Elba, Jacques Mayol filled his lungs once and dropped toward a hundred meters of black water. He carried no tank and no air, only the single breath and a weighted sled pulling him toward the bottom. At forty-nine he was about to go deeper on one lungful than any human had gone, into a pressure that should have crushed the calm out of anyone.

But his calm wasn’t crushed. His heart slowed instead. Sixty beats a minute at the surface, twenty-seven near the bottom. Mayol had trained for years with a yogi in India, practicing pranayama, until he could reach into his own body and turn the dial. Other men fought the sea. He stilled himself and let it carry him. He held that the breath governs the body and the mind both, and that the man who rules his breathing rules everything downstream of it.