The Truth About Hyperventilation and Why You Shouldn’t Do It

Photo Courtesy: Annie Grevers

By Jane Ehret, Medical Student, St. George’s University, Class of 2020.

A recent fad to hit the swimming community is more dangerous than one would think. Over the past few years, it has become increasingly popular to hyperventilate immediately before racing in an effort to improve cardiovascular performance. The reasoning behind such practice is futile, while the potential consequences, lethal.

“Hypoxic blackout” refers to a sudden loss of consciousness often resulting in the drowning of even the most skilled swimmers. Such incidents of drowning have nothing to do with one’s ability to swim, but everything to do with basic human physiology.

As swimmers, we’re always looking for ways to combat the “lactic acid” that inevitably builds up as we race. Have you noticed how your breathing rate increases as your lactate levels rise halfway through that 200 fly? This respiratory reflex is your body’s natural response to elevated lactic acid in the blood.

Just like the chlorinated pool water we swim in, the pH of our blood needs to be in a specific range for everything to work properly. The body is programmed to maintain a homeostatic pH of around 7.4, with lower pH’s being acidosis and higher pH’s being alkalosis. The primary way our body regulates pH is through respiration. Inhale oxygen, exhale carbon dioxide. So the faster you breathe, the more CO2 you “blow off.”

Think of CO2 as an acid: the faster you breathe, the more CO2 you lose, and the less acid is in your blood, meaning the pH is higher. This is called respiratory alkalosis (an elevated blood pH due to rapid breathing). The proposed rationale behind hyperventilating is that you transiently establish a state of respiratory alkalosis before diving in. This is incorrectly presumed to delay the onset of lactic acidosis and improve performance. However, human physiology is much more complex than that.


The medulla oblongata is the respiratory control center in the brain. Sensors throughout the body constantly detect the levels of oxygen and carbon dioxide, and respond appropriately. What most people do not know is that carbon dioxide, NOT oxygen, is the main stimulator for respiration. In fact, oxygen has very little effect on the respiratory drive. This is why your breathing rate increases as the lactic acid builds up in your blood. Your body is compensating for the acidosis by expelling CO2, an attempt to return the pH back to normal.

Because the medulla oblongata relies primarily on carbon dioxide to stimulate diaphragmatic contractions for inspiration, lack of carbon dioxide—which occurs with hyperventilation—eliminates the stimulus to breathe at all. This is particularly dangerous when combined with increased oxygen demand during strenuous activity.

Having a reduced respiratory drive and an increased need for oxygen is a recipe for disaster, ultimately resulting in loss of consciousness. One can extrapolate how such conditions are particularly dangerous for swimmers, as a sudden loss of consciousness can quickly lead to drowning, otherwise known as hypoxic blackout.

— Click Here to Learn More About Hypoxic Blackout.

1 comment

  1. avatar

    Someone should warn Wim Hoff!!!!