Can Breath Training Improve Your VO2 Max? Here's What the Research Says
VO2 max is often described as one of the best measures of cardiovascular fitness. But for many people, it can also be one of the most confusing. You may have heard that a higher VO2 max is linked to better endurance and overall fitness.
But what happens when your VO2 max is low? And why does it sometimes seem so hard to improve, even when you’re exercising regularly?
The answer may involve more than training harder. VO2 max depends on how well your body takes in oxygen, moves it, and uses it during exercise. Your breathing patterns may also affect how efficiently you breathe during exercise and how hard it feels.
In this article, we’ll explore common reasons VO2 max can stall and examine how breathing may influence it.
What Is VO2 Max and Why Does It Matter?
VO2 max is the maximum amount of oxygen your body can take in, transport, and use during intense exercise. It is considered the gold standard of aerobic fitness and one of the strongest indicators of endurance and cardiovascular health.
However, VO2 max is not solely determined by the volume of air inhaled. It reflects the efficiency with which oxygen is transported from the lungs to the muscles, as well as the effectiveness of muscular oxygen utilization for energy production.
Several systems influence this process:
- Cardiovascular fitness and blood flow
- Oxygen transport through the blood
- Muscular oxygen extraction
- Breathing efficiency and respiratory mechanics.
At rest, a young healthy person consumes about 0.15-0.4 liters of oxygen per minute. During exercise, oxygen demand rises substantially. Heart rate and respiratory rate increase, and muscles extract more oxygen from the bloodstream.
Regular aerobic training facilitates physiological adaptations, such as improved circulation, increased capillary density, and enhanced muscular oxygen utilization.
VO2 max depends on several factors, not just genetics. Breathing patterns, recovery quality, training history, body composition, and cardiovascular function all play a role.
Reduced aerobic fitness often results in increased perceived exertion during physical activity.
Common indicators include:
- Getting out of breath quickly
- Fatiguing earlier during workouts
- Poor recovery between efforts
- Reduced stamina and exercise tolerance
Research has linked low VO2 max to adverse long-term health outcomes, such as increased cardiovascular risk and reduced longevity. Consequently, improving aerobic fitness is important for both athletes and individuals seeking to maintain health as they age.
Why Your VO2 Max Is Not Improving
Many assume increasing training intensity or volume will resolve fitness plateaus. However, aerobic fitness may stagnate due to factors beyond training volume, and breathing efficiency is often a critical overlooked component.
You are breathing too much during exercise
Breathing more than you need, especially at easy and moderate intensities, is often overlooked. Although rapid mouth breathing may feel like increased oxygen intake, it does not necessarily improve oxygen delivery to muscles.
At rest and at easy intensities, breathing more than the body needs lowers blood carbon dioxide levels. Although often seen as waste, carbon dioxide plays a role in oxygen delivery through the Bohr Effect.
When CO2 drops too low, hemoglobin binds oxygen more tightly, which can reduce oxygen release to the tissues. During hard exercise, the picture is different: heavier breathing is a normal and necessary response to the body's demands, and it helps offset the build-up of acid in the blood.
Poor tolerance of air hunger is driving heavy breathing
A strong, early reaction to rising carbon dioxide and air hunger can cause premature heavy breathing during exercise. In Oxygen Advantage, "CO2 tolerance" is a practical training term for staying comfortable as air hunger builds. It is not the same as a laboratory measure of CO2 sensitivity.
Low tolerance of air hunger can lead to:
- Early breathlessness
- Reduced exercise economy
- Faster fatigue
- Feeling out of control of your breathing
Breathlessness during exercise has several drivers, including breathing pattern, chemical signals, respiratory muscle fatigue, and how the brain perceives the sensation. Sometimes exercise feels limited as much by breathlessness as by the heart or legs.
Improving tolerance to carbon dioxide may help the body stay calmer and more efficient during physical effort.
You are not recovering properly
Aerobic improvements happen during recovery, not during the workout itself. If the body stays under constant physical or psychological stress, progress can stall despite training quality.
Poor sleep, excessive intensity, nervous system overload, and chronic stress interfere with adaptation.
This often shows up as:
- Persistent fatigue
- Heavy legs during training
- Poor sleep quality
- Reduced motivation
- Feeling exhausted rather than energized after exercise
Sometimes the problem is not undertraining but under-recovering.
Mouth breathing is reducing exercise efficiency
Most people switch to mouth breathing as exercise intensity rises, often before it is necessary. Nasal breathing may offer advantages that support breathing efficiency and exercise economy.
The nose helps:
- Warm and humidify incoming air
- Filter airborne particles
- Produce nitric oxide, which supports circulation and airway function
- Naturally slow the breath
Research suggests nasal breathing may reduce unnecessary ventilation and improve oxygen use efficiency during exercise. This is why many athletes now use mouth tape for sports.
Furthermore, nasal strips for sports are also effective for reducing mouth breathing during exercise. Read our full guide on nose strips for athletes and sports performance.
A 2018 study examined ten recreational runners who trained exclusively with nasal breathing for six months. When tested breathing through the nose, their VO2 max and peak exercise performance were not significantly different from mouth breathing (VO2 max was around 7% lower, but the difference was not statistically significant), while they breathed more efficiently overall.
Compared with mouth breathing, nasal breathing resulted in:
- Lower breathing rates
- Reduced ventilation volume
- Better oxygen extraction per breath
- Improved physiological economy during exercise
A key finding was that athletes achieved similar performance with significantly less breathing. Nasal breathing did not increase VO2 max but improved breathing efficiency and exercise economy, helping exercise feel more controlled and sustainable.
Nasal breathing does have limits. In a 2025 study of healthy adults who were not adapted to nasal breathing, breathing only through the nose reduced peak ventilation, peak oxygen uptake and peak workload during a maximal test, because the nose could not move enough air (Mapelli et al., 2025, PLoS One). At maximal intensity, mouth breathing is normal and necessary.
Dysfunctional Breathing Patterns Are Limiting Performance
How you breathe matters as much as how much you breathe. Upper chest, shallow, and irregular breathing patterns are common, especially in stressed people or those untrained in breathing mechanics.
These patterns increase the workload on the respiratory system and reduce efficiency during exercise.
Over time, dysfunctional breathing can:
- Increase fatigue
- Waste energy
- Amplify breathlessness
- Reduce exercise economy
Research in sports physical therapy has suggested that breathing dysfunction should be addressed before correcting movement or performance limitations because breathing mechanics influence the entire system.
Other Reasons Why VO2 Max Can Decline Over Time
VO2 max naturally changes with age, but several lifestyle factors may accelerate the decline.
These include:
- Physical inactivity
- Chronic stress
- Poor sleep
- Illness and post-viral fatigue
- Weight gain
- Sedentary lifestyle
- Poor breathing habits
Habitual mouth breathing and chronic overbreathing may gradually reduce oxygen efficiency, making physical activity feel harder over time.
How Breathing Affects VO2 Max
VO2 max is not simply a measure of how much oxygen enters the lungs. It reflects how efficiently oxygen is delivered, released, and used throughout the body. Breathing mechanics influence how economical and controlled this process feels.
The Bohr Effect
The Bohr Effect describes how carbon dioxide and acidity help oxygen separate from hemoglobin and move into the muscles. When breathing is excessive at rest or easy intensities and CO2 levels drop too low, oxygen release becomes less efficient.
The Bohr Effect is one part of oxygen delivery, which also depends on cardiac output, blood oxygen content, blood flow and how much oxygen the muscles extract. Higher CO2 does not on its own increase VO2 max, and heavier breathing during hard exercise is a normal part of meeting demand.
Nasal Breathing and Oxygen Uptake
Nasal breathing naturally slows airflow and creates more resistance than mouth breathing. This may improve gas exchange and support better respiratory control during exercise.
The nose also produces nitric oxide, which helps widen blood vessels and airways, supporting circulation and oxygen transport.
Research suggests nasal breathing may:
- Reduce breathing effort
- Improve oxygen extraction
- Increase breathing efficiency
- Improve exercise and running economy
Although it can feel uncomfortable initially, the body can adapt surprisingly well to nasal breathing during exercise.
Diaphragmatic Breathing and Endurance
The diaphragm is the primary muscle involved in breathing. When breathing becomes shallow or chest-dominant, the body recruits smaller accessory muscles that fatigue more easily.
Diaphragmatic breathing allows air to move deeper into the lungs, where gas exchange is most efficient. It may also:
- Reduce the energy cost of breathing
- Improve posture and movement quality
- Lower tension in the neck and shoulders
- Support better endurance during exercise.
The Oxygen Advantage® method often emphasizes light, slow, and deep breathing rather than fast, excessive breathing.
Breathing Efficiency and Exercise Economy
Breathing itself requires energy. The harder the respiratory muscles work, the more oxygen they consume.
A more efficient breathing pattern can achieve the same workload with less breathing effort, improving exercise economy and helping preserve energy during training or competition.
Staying calm as air hunger builds is an important part of this process, because it helps breathing remain more controlled as intensity rises.
The Oxygen Advantage®: Breathing Training for Efficiency and Performance
Most training programs focus on mileage and intensity. The Oxygen Advantage® method takes a different approach by focusing on how efficiently the body uses oxygen during exercise.
This distinction matters. Research suggests breathing training is unlikely to dramatically increase your VO2 max ceiling alone. It may help you perform more efficiently at your current capacity by reducing breathing energy cost, improving breathing control, and helping you tolerate breathlessness during exercise.
The Oxygen Advantage® Method focuses on:
- Nasal breathing during exercise
- Improving carbon dioxide tolerance
- Functional diaphragmatic breathing
- Reduced breathing exercises
- Breath-hold training combined with physical conditioning
- Faster recovery through slow nasal breathing
The strongest evidence for the method concerns breathing economy. In the same 2018 study of recreational runners who trained exclusively with nasal breathing for 6 months, VO2 max and peak performance were not significantly different with nasal breathing, while ventilation was around 22% lower. They did not increase their aerobic ceiling but achieved similar output with less breathing.
Patrick McKeown, founder of the Oxygen Advantage® method, explains simply: calm breathing conserves energy. During intense exercise, inefficient breathing can consume much oxygen that could support working muscles.
Over time, many athletes report:
- Lower breathing rates during exercise
- Reduced breathlessness at higher intensities
- Better recovery between hard efforts
- Improved exercise economy
- Greater control under physical stress
Nasal Breathing Training
Nasal breathing is the foundation of the Oxygen Advantage® method. With consistent practice over weeks, many people find they become more comfortable with air hunger and breathe less unnecessarily at easy and moderate intensities.
The goal is not to restrict performance but to make breathing more efficient so the same workload requires less effort. Research suggests athletes who adapt to nasal breathing can maintain similar peak performance while breathing more calmly and economically.
Reduced breathing exercises
Reduced breathing exercises create mild, controlled air hunger by deliberately breathing less than the urge demands.
The goal is not oxygen deprivation but to become comfortable with slightly higher carbon dioxide levels and mild air hunger without triggering heavy breathing.
Over time, this may:
- Reduce overbreathing
- Improve respiratory control
- Help you stay calm as breathlessness builds
- Improve exercise economy
This is a core Oxygen Advantage® method for improving breathing efficiency without increasing training load.
Breath hold training
Breath-hold exercises are designed to simulate some of the physiological effects associated with altitude training. Research and performance observations suggest breath holds may:
- Improve tolerance to breathlessness
- Strengthen breathing muscles
- Improve running economy
- Support aerobic and anaerobic conditioning.
Strong breath holds are not suitable for everyone. Avoid them if you have a heart condition, high or low blood pressure, epilepsy, or another serious medical condition, or if you are pregnant, unless cleared by your doctor. Never practice them in or under water.
Recovery breathing
Breathing also influences recovery after exercise.
Slow nasal breathing with longer exhalations may help:
- Calm the nervous system
- Reduce stress hormones
- Improve recovery between sessions
- Support better sleep quality.
Recovery is where aerobic adaptation happens, so improving recovery quality may support long-term improvements in endurance and aerobic fitness.
Train Your Breathing. Perform Better.
If your VO2 max is not improving, breathing training is unlikely to raise it dramatically on its own. But focusing only on VO2 max may miss the bigger picture. Performance is not only about building a bigger engine. It is also about using the engine you already have more efficiently.
Better breathing can help reduce the energy cost of exercise, improve breathing control, and make breathlessness easier to manage during hard efforts.
When breathing becomes inefficient, the respiratory muscles demand more oxygen, leaving less available for movement and performance. Oxygen Advantage® focuses on improving:
- Breathing efficiency during exercise
- Tolerance to breathlessness and carbon dioxide
- Recovery between efforts
- Exercise economy and endurance
- Control under physical stress
Research and instructor experience point to similar patterns. Athletes often report lower breathing rates during exercise, reduced breathlessness, improved recovery between hard efforts, and better endurance at the same training intensity.
For most people, the biggest benefit is not necessarily a higher VO2 max score. It is being able to train, move, and perform more efficiently with the aerobic capacity they already have.
Oxygen Advantage® provides a practical, science-based way to train the respiratory system so breathing becomes calmer, more efficient, and more supportive of performance.