How you breathe during exercise affects how you pace, perform and respond to increasing intensity. Here's what happens to your breathing when you work out—and what the science says about breathing techniques.
Why Do You Breathe Harder During Exercise?
At rest, breathing is something you barely notice.
Start running, and suddenly you're aware of every breath.
As exercise intensity increases, your muscles need more energy. They consume more oxygen and produce more carbon dioxide (CO₂). Your cardiovascular and respiratory systems respond by increasing blood flow and ventilation—the amount of air you move in and out of your lungs each minute.
The relationship between the two systems is closely coordinated. As your metabolic rate rises, both cardiac output and ventilation increase to support oxygen delivery and CO₂ removal.
That's why an easy jog can feel almost effortless from a breathing perspective, while a hard interval can leave you struggling to get enough air.
You're not simply "running out of oxygen."
Your body is responding to a much greater metabolic demand.
How Oxygen and CO₂ Affect Breathing During Exercise
Oxygen tends to get all the attention when we talk about exercise and breathing.
CO₂ matters too.
As your muscles work harder, they produce more CO₂. Your body needs to remove it, and ventilation plays an important role in maintaining the balance of gases in your blood and regulating acid-base balance.
As exercise intensity increases, ventilation eventually begins to rise disproportionately to oxygen consumption. This is one of the physiological changes associated with reaching higher exercise intensities.
This is also where the term CO₂ tolerance often enters the conversation.
In fitness and breathwork circles, CO₂ tolerance is sometimes described as the ability to remain comfortable as CO₂ rises and the urge to breathe increases. But it shouldn't be interpreted as a reason to suppress breathing or deliberately expose yourself to dangerously high CO₂ levels.
Your body already has sophisticated mechanisms for regulating breathing during exercise.
For most athletes, the useful takeaway is simpler: your breathing response is part of how your body regulates the increasing demands of exercise.
Can Your Breathing Actually Limit Performance?
For most healthy people exercising at moderate intensities, the respiratory system has considerable capacity.
As exercise gets harder, however, breathing itself requires more work.
Your diaphragm and other respiratory muscles have to move increasingly large volumes of air. During strenuous exercise, the work required to breathe can become substantial, and respiratory muscle fatigue can contribute to overall exercise fatigue in certain conditions.
This is particularly relevant to endurance athletes and prolonged high-intensity exercise.
But it's important not to overstate the role of breathing.
For most recreational athletes, performance isn't limited by the lungs alone. Cardiovascular fitness, muscular endurance, exercise intensity, pacing and accumulated fatigue all contribute to how difficult a session feels.
Breathing is part of the performance system—not a separate switch you can simply optimise.
Why Do I Get Out of Breath So Quickly When I Exercise?
Getting out of breath during exercise isn't necessarily a sign that you're breathing incorrectly.
It can simply mean that the intensity is high relative to your current fitness.
If you're new to running, for example, even a relatively slow pace may push your cardiovascular system hard enough to make breathing rapid and uncomfortable. As your aerobic fitness improves, that same pace should generally require less relative effort.
Breathing can therefore give you useful information about exercise intensity.
If an easy run consistently leaves you struggling to speak, you may be running harder than intended. If you can comfortably speak in sentences, you're generally working at a lower intensity than when conversation becomes difficult.
This isn't a substitute for heart-rate monitoring or laboratory testing, and the relationship between speech and exercise intensity varies between individuals. But as a practical tool, it can help you recognise when your effort is drifting higher.
If breathlessness is severe, unusual for the level of exercise, or occurs with symptoms such as chest pain, dizziness or fainting, that's different—and worth discussing with a healthcare professional.
How to Breathe While Running
There's no single breathing pattern that every runner needs to follow.
At an easy pace, breathing may feel relaxed and relatively controlled. As your pace increases, your breathing naturally becomes deeper and faster.
Rather than trying to force a particular rhythm, focus first on matching your breathing to your effort.
For easy running, you should generally be able to maintain a conversation without significant difficulty. As the intensity rises, you'll naturally move towards heavier breathing.
Some runners find it useful to coordinate their breathing with their stride—for example, taking a set number of steps while inhaling and exhaling. This can help create a sense of rhythm, but there's limited evidence that one specific breathing pattern universally improves running performance. A 2022 review of breathing strategies in running found that the evidence for purposeful breathing techniques improving performance remains limited and mixed.
In other words, don't let breathing technique become another thing you have to overthink.
Your pace is usually the bigger variable.
Nasal Breathing vs. Mouth Breathing During Exercise
Nasal breathing has become one of the more popular topics in the fitness world.
The appeal is understandable. Breathing through the nose warms, humidifies and filters incoming air, and nasal breathing can be comfortable during rest and lower-intensity exercise.
But the claim that you should always breathe through your nose during exercise doesn't hold up.
As exercise intensity rises, your body needs to move much more air. At higher intensities, breathing through both the nose and mouth is a normal response that allows ventilation to increase substantially.
A recent review of research on nasal and oral breathing found that the effects vary according to exercise intensity and the outcome being measured, rather than supporting a simple "nasal is better" conclusion.
The practical takeaway is straightforward:
Use nasal breathing when it feels comfortable. Don't force it when the intensity demands more ventilation.
Your breathing pattern should support the exercise—not become a test of discipline.
Can You Train Your Breathing?
Yes—but there's a difference between breathing exercises and respiratory muscle training.
Respiratory muscle training (RMT) uses structured exercises to challenge the muscles involved in breathing, particularly the muscles responsible for inhalation.
Research suggests that RMT can improve respiratory muscle strength and endurance, and some studies have found improvements in endurance performance. A 2012 systematic review and meta-analysis of healthy individuals found that RMT improved endurance exercise performance, with greater benefits generally observed in less-trained participants.
More recent research has continued to find improvements in respiratory muscle function among athletes, although the quality of evidence varies and many studies involve specific sports or relatively small groups. A 2025 systematic review and meta-analysis of 25 studies involving 522 athletes concluded that RMT can improve measures of respiratory muscle function, while noting that the evidence for performance benefits remains low to very low quality.
For the average runner or gym-goer, that doesn't mean you need to add another complicated protocol to your training.
Consistent aerobic training remains the foundation.
As your fitness improves, you'll be able to sustain a higher workload before breathing becomes heavily laboured. That's an adaptation to training—not a breathing trick.
The Takeaway
You don't need to micromanage every breath during a workout.
Your body is remarkably good at adjusting ventilation to the demands of exercise. Your breathing gets deeper and faster because your muscles are working harder, your metabolism is changing and your body needs to manage oxygen and CO₂ more rapidly.
Instead, learn to listen to your breathing.
It can tell you when an easy run isn't so easy anymore. It can help you gauge effort. And when exercise becomes very intense, it gives you a window into just how hard your body is working.
Breathing isn't a performance hack.
It's part of the performance system.
And understanding it can help you train with a little more awareness.
References
1. Sheel AW, Angus SA. (2026). Breathing during Exercise: Respiratory and Circulatory Interactions. Physiology.
2. Harbour E, Stöggl T, Schwameder H, Finkenzeller T. (2022). Breath Tools: A Synthesis of Evidence-Based Breathing Strategies to Enhance Human Running. Frontiers in Physiology.
3. Cross TJ, et al. (2023). A Systematic Review of Methods Used to Determine the Work of Breathing during Exercise.Medicine & Science in Sports & Exercise.
4. Illi SK, Held U, Frank I, Spengler CM. (2012). Effect of respiratory muscle training on exercise performance in healthy individuals: a systematic review and meta-analysis. Sports Medicine.
5. Romer LM, et al. (2012). Effects of respiratory muscle training on performance in athletes: a systematic review with meta-analyses.
6. Xavier DM, et al. (2025). The effectiveness of respiratory muscular training in athletes: A systematic review and meta-analysis. Journal of Bodywork and Movement Therapies.
7. Effects of Nasal and Oral Breathing on Respiratory Muscle and Brain Function: A Review. (2025). Turkish Journal of Thoracic and Cardiovascular Surgery.
