What Doesn't Kill Us

by Scott Carney

Luckily for the human subjects of Swedish-born physiologist Per Scholander, testing methods had gotten more sophisticated over the intervening century. Instead of binding his volunteers to death, he used lab equipment to measure the heart rates and oxygen levels of volunteers while they dove to the bottom of a pool. The second that the cool water covered their faces, Scholander noticed an immediate and corresponding decrease in their heart rates. It was the same phenomenon that Richet has seen with his ducks. In the second phase of the experiment Scholander installed a few pieces of fitness gear at the bottom of the pool and told his subjects to work out while underwater. While the toil of lifting weights underwater must have been awkward, the heart monitors showed that no matter how vigorous their activity was, their heart rates remained suppressed. Not only that, the volunteers also experienced vasoconstriction while beneath the surface of the water as the blood from their extremities shunted toward their core. The water, it turned out, triggered a series of physical changes in his subjects that advantageously prepared them to survive in a hostile underwater environment where breathing would mean death. It’s a reflex that Scholander named “the master switch of life,” a term that has since been taken up by a burgeoning free-diving community that depends on these built-in changes in the body to extend the duration of their underwater forays. Freedivers, described masterful...