When our lungs are filled with air while swimming, we are suspended in the water. In other words, we weigh zero. When we completely exhale all the air, even with some residual air in our lungs, our total body weight is around 8-9 pounds in water, and we sink.
With higher buoyancy (air in lungs), we also cause less frontal drag as we move through the water, so it would make sense to keep all of that air in our lungs after we plant our faces back in the water after the breath. After all, we weigh less and we are more buoyant with all of that air in our lungs. But that is not what elite swimmers do.
Virtually all of the elite swimmers of the world, whether swimming freestyle, breaststroke or fly, breathe by releasing air bubbles from their noses immediately after the face returns to the water. Since the bodies are moving forward in the water, those air bubbles travel below the bodies and beneath the chests of the swimmers, until they finally make their way to the surface around the body. The reason that the swimmers breathe by releasing some air from their noses is to reduce frontal drag.
A few years ago, while doing my workout in Islamorada, Florida, at the Founders Park Pool, one of the regular Masters swimmers, Chris Olstad, who is an oceanic researcher there, asked me a question.
“When Sun Yang swims freestyle, he releases air from his nose and it goes under his body. Do you think that he does that for the same reason that the emperor penguins release air from under their feathers in the Antarctic?”
I had no idea what he was talking about. Frankly, I had never noticed nor paid attention to those air bubbles from Sun Yang or any other swimmer.
“What do you mean”, I asked?
“The emperor penguins have this amazing ability to trap air under their feathers while swimming in the water”, he continued. “When the leopard seals start chasing them for lunch, the penguins release the air from under their feathers, surrounding their small bodies with air bubbles, which reduces their frontal drag and enables them to increase speed tremendously. They then fly out of the water and on to the ice, out of harm’s way.”
That is when I started paying attention to the air bubbles being released through the nose with each breath by elite swimmers under water and realized that they all are all doing that. I also did some research and discovered that large cruise ships, cargo ships and other boats do the same thing. They create aerators along the hull which, through cavitation, release bubbles that reduce drag by about 10%. 
Then we did our own testing. Using our Drag/Propulsion Meter technology, we pulled a swimmer across a 50-meter pool at 2.3 meters per second in a fixed, streamlined body position, measuring the frontal drag forces at each .05 seconds. First, we measured drag with air in the lungs. Then we repeated the test while he released air bubbles from his nose under his body. Similar to the maritime study, we found a drag reduction of 9.3% with the bubbles under the body, consistent with their findings.
Presumably, with the air bubbles under the chest, while still providing the same or similar buoyancy effect as if the air were in the lungs, the bubbles also change the medium through which the swimmer is moving. The bubbles likely alter the boundary layer that impacts the pressure drag, the greatest contributor to frontal drag of a swimmer at race speed.
After taking your low-profile breath, tuck your chin down toward your chest to get your head under water and release some air through your nose, not your mouth. Air released from your mouth will likely rise immediately to the surface on either side of your face. Breathe by releasing some air through your nose. You should feel the air bubbles go under your chest. Then, burst exhale just before turning your head for the next quick air exchange.
At the speed you are swimming you may not reduce frontal drag by 10%, but, with the compelling frontal drag forces that are encountered in water, you should be happy take any drag reduction you can get from breathing while swimming freestyle.
Yours in Swimming,
Gary Hall Sr., M.D. is a three-time Olympic swimmer (‘68, ‘72, ‘76) who earned a medal in each of the three Olympic Games. At one time he held 10 world records in all strokes except breaststroke and was the World Swimmer of the year in 1969 and 1970.
The views expressed in this article are the opinion of the author and not necessarily the practices of USA Triathlon. Before starting any new diet or exercise program, you should check with your physician and/or coach.
 Lebkowski, A, Researching the Impact of Electric Boat Hull Aeration Energy Consumption, Scientific Journal of Gdynia Maritime University, No. 98, March 2017