Walk into almost any commercial gym at peak hours, and you’ll hear it: a sudden guttural grunt slicing through the hum of treadmills and clanking plates. Sometimes it accompanies a heavy deadlift or chest press. Othertimes, a pec deck set that barely warrants a raised eyebrow, let alone a primal yell.
So, when is it OK to grunt, and is it fair that you are annoyed by hearing others do it? According to James Nestor, New York Times bestselling author of Breath and one of the leading voices in modern breathing science, the answer has less to do with gym etiquette and more with pressure, physiology, and control.
“Grunting can help only when it’s an accidental byproduct of good breathing,” Nestor explained to Muscle & Fitness.
That distinction between accident versus intention may be the clearest line between performance breathing and what Nestor calls performative breathing.
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The Role of Intra-Abdominal Pressure in Heavy Lifting
At the center of the debate, Nestor explains, is intra-abdominal pressure. Heavy lifting demands a stable, pressurized torso that protects the spine and allows force to transfer efficiently.
The diaphragm, an umbrella-shaped muscle beneath the lungs, plays a starring role. When it contracts, it descends, the abdomen expands, and pressure builds around the torso like an inflated column. In layman’s terms, it’s often called belly breathing.
“When this pressure is released slowly through the airway, a sound may occur, one might call a grunt,” Nestor explains. “Grunting is not the goal, but rather the aftereffect of pressure release.”
He further noted that decades of sports science research examining breath control during force production show that brief airway closure or resistance, including techniques similar to the Valsalva maneuver or controlled forceful exhalation, can increase maximal force output, often in the range of 2-10%, depending on the task. Improvements have been documented in measures such as grip strength, isometric force, and explosive power output.
“This isn’t because the sound is loud, but because briefly closing the airway (the glottis) increases pressure inside the torso, which ramps up the ability of muscles to fire harder and more efficiently,” he notes, adding that when the grunt becomes theatrical, something breaks down.
“The moment a grunt becomes intentional, it’s usually a sign that the diaphragm is no longer engaged,” Nestor says. “Breathing shifts upward into the neck, jaw, and face, muscles that were never meant to stabilize heavy loads.”
Does Grunting Increase Strength and Power?
One of the most persistent myths in gym culture is that louder breathing signals greater power. According to Nestor, physiologically, that’s nonsense.
“There is zero evidence that increasing the volume of a grunt yields more endurance,” Nestor says, noting that studies examining breathing strategies during resistance exercise consistently show that coordination and timing matter far more than sound intensity.
He explains that a “functional grunt,” or a short, controlled, conscious yelp, however, may be useful. From a mechanical standpoint, that’s the body’s response to airway resistance. Narrowing the vocal cords during exhalation increases resistance, helping maintain lung inflation and torso stability, similar to pursed-lip breathing used in pulmonary rehabilitation. The effect is comparable to air slowly leaking from a tire rather than rushing out all at once.
“The body doesn’t care about sound. It cares about controlling pressure,” Nestor says, adding that sound is merely a byproduct. When sound comes from throat tension instead of controlled diaphragm engagement, pressure dissipates rapidly, which may result in less stability.
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What Happens When You’re Gasping for Air During a Workout?
Another gym myth is that breathlessness or gasping for air is a sign of a lack of oxygen. According to Nestor, not quite.
“You almost never run out of oxygen,” Nestor says. “What breaks down performance is rising carbon dioxide.”
Rising CO₂ levels stimulate chemoreceptors that trigger an emergency signal in the brain to breathe, shifting the nervous system’s priority from performance to survival. Initially, your brain is telling your body to stop focusing on lifting the weight and just breathe instead. According to Nestor, that’s why elite athletes train specifically to tolerate higher CO₂ levels.
“The more carbon dioxide your body can comfortably tolerate, the more oxygen you will get to your hungry cells, and the longer and stronger you’ll be able to perform,” he says, noting that many of the noises you might hear in the gym, like forced exhales, moans, and grunts, are the result of the body reaching the limit of carbon dioxide tolerance and the brain putting on the emergency break.
Hence, grunting should support the lift, not show it off. “If you’re grunting during warmups, every rep, or whenever people are close, you have an issue, physical or psychological,” Nestor points out, adding that grunting through pain might signal poor load management and breathing mechanics.
How to Breathe Properly During Heavy Lifts
How you breathe should change based on your training program, the load you’re moving, and the physiological demand being placed on your body. Here’s how Nestor breaks down how you should breathe based on your workouts:
Maximal lifts: The priority is pressure and timing. Heavy loads need high internal pressure at the correct time to keep the spine stabilized. This can occur either through a short-term breath hold or through a “leak” exhalation that is timed and deliberate.
Rep work, like AMRAP: The main focus is to complete the greatest number of reps possible during a set time window. This requires a consistent breathing pattern that stays organized and rhythmic while maintaining pressure without leading to panic. Breathing excessively or holding your breath dramatically will often cut the number of sets you complete and limit the total volume.
Endurance and conditioning: Priorities shift to efficient ventilation and the ability to tolerate carbon dioxide. He points to nasal breathing here as it slows down your breathing and makes it more efficient. Plus, it also promotes the release of nitric oxide, which allows your body to go longer and harder without breaking down.
Nestor underscores that studies have shown that when recreational athletes train to use nasal breathing, they are able to reach up to 85% of their maximum oxygen uptake (VO2max) for intense periods of exercise.
“They are often able to achieve the same peak performance and oxygen consumption as when they used mouth breathing; however, they breathed approximately more than 20% less volume during the time,” he explains, adding that the same output for less effort means you can be stronger for longer. But there is a time and place for everything. In upper Zone 4 and Zone 5 training, consciously switching to mouth breathing for short bursts can instill benefits.
When It’s OK to Grunt in the Gym
Before you roll your eyes the next time you hear someone across the gym grunting mid-set, it’s worth considering what that sound might represent. In some cases, it reflects a controlled release of pressure during a demanding effort. In others, it signals a breakdown in breathing mechanics, load management, or nervous system regulation. Don’t be the latter. The difference matters.
“The body doesn’t care about how twisted your face is or the timbre of your voice,” Nestor said. “It only cares about how to generate pressure efficiently, keep the nervous system stable, and support all the mechanisms of the body.”
