When the average person tries to equalize his ears, he puffs out his cheeks and blows hard, so that compressed air enters the sinus cavities that lead to the ears. This method, called the Valsalva maneuver, is used by about 99 percent of the population, and it’s usually effective. But it doesn’t work when you’re freediving past around forty feet. As you dive deeper, air becomes more and more compressed in the lungs, until there isn’t enough left to push into the ears. The Valsalva method becomes useless.
