In the relentless pursuit of athletic advantage, a surprisingly simple method is gaining prominence among elite competitors and everyday fitness enthusiasts alike: breathing, or more specifically, not breathing. Carbon dioxide tolerance training, a method centered around controlled breath holds and restricted breathing patterns, is transforming how athletes train their respiratory systems and challenging conventional wisdom about optimal performance.
This approach, which deliberately increases carbon dioxide levels in the bloodstream through specific breathing protocols, has roots in freediving techniques but has evolved into a sophisticated training methodology with applications across virtually every sport. As research accumulates and high-profile athletes share their success stories, CO2 tolerance training is emerging from niche practice to mainstream training essential.
The science behind carbon dioxide tolerance
At its core, carbon dioxide tolerance training works by manipulating the body’s respiratory drive. Contrary to popular belief, it’s not low oxygen levels that primarily trigger the urge to breathe, but rather rising carbon dioxide concentrations in the bloodstream. By systematically exposing the body to higher-than-normal CO2 levels through controlled breath holds or restricted breathing exercises, athletes can effectively reset their respiratory sensitivity.
The body adapts to these controlled stresses by becoming more efficient at carbon dioxide buffering, the process of managing blood pH levels when CO2 builds up. This adaptation has cascading effects throughout the physiological systems that contribute to athletic performance, from oxygen utilization to lactic acid management.
Research from the University of Colorado’s Altitude Research Center has demonstrated that regular exposure to elevated CO2 levels can increase the body’s buffering capacity by up to 18% after just four weeks of consistent training. This improved buffering ability allows athletes to maintain performance during high-intensity efforts when CO2 levels naturally spike.
The 7 key benefits of carbon dioxide tolerance training
Research and real-world application have identified several significant benefits from implementing CO2 tolerance training. These advantages extend across performance domains and appear to benefit athletes across various sports and disciplines.
Enhanced oxygen utilization efficiency: One of the most immediate benefits of CO2 tolerance training is improved oxygen utilization. Through a phenomenon known as the Bohr Effect, increased carbon dioxide levels in the bloodstream actually enhance oxygen delivery to working muscles by facilitating the release of oxygen from hemoglobin.
Athletes who engage in regular CO2 tolerance training report being able to maintain performance with fewer breaths, essentially getting more work output per oxygen molecule. Measurements of arterial oxygen saturation during exercise show that trained individuals maintain higher saturation levels during intense efforts, suggesting more efficient oxygen extraction by tissues.
This improved efficiency translates directly to performance, particularly in endurance sports where oxygen delivery is often the limiting factor. Runners, cyclists, and swimmers who incorporate CO2 training have shown improvements in time-to-exhaustion tests ranging from 8-12% in various studies.
Increased anaerobic threshold: Perhaps the most performance-relevant benefit is the documented increase in anaerobic threshold, the intensity at which the body begins to accumulate lactate faster than it can clear it. CO2 tolerance training appears to push this threshold higher, allowing athletes to work at greater intensities before experiencing the performance-limiting effects of lactate buildup.
This adaptation occurs through multiple mechanisms, including enhanced buffering capacity and improved mitochondrial function. Athletes who regularly practice CO2 training protocols report being able to sustain higher outputs before experiencing the familiar burn of intense effort, a subjective experience supported by blood lactate measurements in laboratory settings.
Respiratory muscle conditioning: The respiratory muscles, primarily the diaphragm and intercostals, respond to CO2 tolerance training just as other muscles adapt to resistance training. These muscles become stronger, more efficient, and more resistant to fatigue through the controlled stress of restricted breathing exercises.
This conditioning directly addresses a limiting factor many athletes experience: respiratory muscle fatigue. During high-intensity exercise, the respiratory muscles can demand up to 15% of cardiac output, competing with locomotor muscles for blood flow and oxygen. By training these muscles specifically, athletes can delay respiratory fatigue and maintain performance longer.
Testing protocols measuring maximum voluntary ventilation (MVV) have shown increases of 19-23% in respiratory muscle work capacity after eight weeks of dedicated CO2 tolerance training, translating to improved performance particularly in the latter stages of endurance events.
Enhanced mental resilience: Beyond the physiological benefits, CO2 tolerance training offers powerful psychological advantages. The controlled discomfort of breath restriction serves as a form of stress inoculation, training athletes to maintain focus and technique even when physiological alarms are sounding.
This mental training aspect may be particularly valuable in competition settings, where maintaining composure under physical duress often separates top performers. Athletes report improved ability to push through perceived limits and maintain technique under fatigue after incorporating CO2 training into their regimens.
Research in sports psychology has demonstrated that regular exposure to the controlled stress of CO2 training activates the parasympathetic nervous system over time, essentially teaching the body to remain calm in uncomfortable situations, a valuable skill in any competitive context.
Improved recovery capacity: Interestingly, CO2 tolerance training appears to enhance recovery between intense efforts. By improving respiratory efficiency and blood flow regulation, athletes can clear metabolic byproducts more effectively during recovery intervals, allowing for higher quality training sessions with less accumulated fatigue.
Interval workouts that incorporate restricted breathing during recovery periods have shown particular promise, with athletes able to maintain higher powers or speeds in subsequent work intervals compared to those using conventional recovery breathing.
This improved recovery capacity extends beyond individual training sessions, with practitioners reporting enhanced recovery between training days as well. This adaptation may be related to improved autonomic nervous system regulation, as measured by heart rate variability improvements in regular practitioners.
Reduced exercise-induced asthma symptoms: For athletes who suffer from exercise-induced bronchoconstriction (EIB), a common condition where breathing passages narrow during exercise, CO2 tolerance training offers particular benefits. The controlled hypercarbia (elevated CO2) appears to reduce bronchial sensitivity and improve symptoms in many affected athletes.
This improvement likely stems from the bronchodilating effect of carbon dioxide, as well as the gradually increasing tolerance to the sensation of restricted breathing. Athletes with EIB who incorporate CO2 training report fewer episodes and less severe symptoms, particularly in challenging environments like cold weather or high pollen conditions.
Enhanced altitude performance: Athletes competing at altitude face the dual challenge of reduced oxygen availability and respiratory alkalosis, an increase in blood pH due to the natural tendency to hyperventilate in low-oxygen environments. CO2 tolerance training directly addresses this challenge by improving the body’s ability to maintain optimal blood pH despite altered breathing patterns.
By reducing respiratory sensitivity to CO2, athletes can avoid the performance-hindering effects of unnecessary hyperventilation at altitude. Studies comparing altitude performance in trained and untrained individuals show that those with CO2 tolerance training experience less performance decrement and adjust to altitude conditions more quickly.
Implementing CO2 tolerance training safely
While the benefits are compelling, experts emphasize that proper implementation is crucial for both safety and effectiveness. CO2 tolerance training should always be approached systematically, with appropriate progression and ideally with initial guidance from experienced coaches.
Most protocols begin with simple breath-holding exercises that gradually increase in duration, followed by more advanced techniques like restricted breathing during exercise. The common thread is a gradual, progressive exposure to elevated CO2 levels that allows the body to adapt safely.
It’s critically important to note that all structured training should take place in safe environments, never in water unless under proper supervision. The risk of shallow water blackout makes unsupervised underwater breath-holding exercises extremely dangerous. Similarly, breath-holding should never be preceded by hyperventilation, which can suppress the protective urge to breathe.
Training methods and protocols
Effective CO2 tolerance training typically involves several approaches, used either independently or in combination depending on the athlete’s goals and sport requirements.
Static breath holds, typically measured using the “CO2 tables” popularized by freediving training, involve holding the breath for increasing durations with short recovery periods between efforts. These tables systematically increase CO2 levels and train the body to buffer more effectively.
Dynamic breath restriction incorporates controlled breathing patterns during exercise, for example, limiting breaths to every fourth stroke while swimming or using breath-per-step ratios while running. These approaches specifically target sport performance by simulating the respiratory challenges of competition.
More advanced practitioners may use specialized devices that create additional respiratory resistance or modify inspired air composition, though these approaches require more careful implementation and monitoring.
The future of respiratory training
As interest in CO2 tolerance training grows, technology is making the practice more accessible and measurable. Wearable devices now offer real-time feedback on blood oxygen saturation, respiratory patterns, and even estimated blood gas levels, allowing for more precise training and clearer progress tracking.
Research continues to explore new applications, with particular interest in the method’s potential benefits for conditions like anxiety, sleep apnea, and even certain neurological disorders. The powerful effects of respiratory training on the autonomic nervous system suggest applications well beyond sports performance.
For athletes seeking every legitimate advantage, carbon dioxide tolerance training represents a frontier that bridges ancient breathing wisdom with cutting-edge physiology. As one of the few remaining areas in elite training with substantial room for optimization, respiratory training may well represent the next evolution in athletic performance enhancement.
