Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance

by Alex Hutchinson

A famous 1997 study at Yale had subjects exercise for two hours to induce dehydration, then allowed them to drink and monitored the changes in perceived thirst and antidiuretic hormone, the two key regulators of plasma osmolality.33 Then they repeated the trial, but inserted a tube down through the nose into the stomach to vacuum out the water as soon as it was swallowed. The result: thirst and antidiuretic hormone secretion both decreased anyway, presumably in response to the sensation of water flowing down the throat. And when they reversed the experiment, sending the same amount of water down the nasogastric tube instead of letting the subjects swallow it, it was less effective in quenching thirst even though the water was allowed to stay in their stomachs.