The Ancient Greeks introduced formal sports to the world with the first Olympic Games in 776 BC (which included events such as foot and chariot races, wrestling, jumping, discus, and javelin throwing). Since then, centuries of attempts to optimize athletes’ successes have occurred, and an entire science has evolved to address the unique needs of the sport’s participants. Today, with advances in science and technology, there are more opportunities than ever to optimize the success of the athlete. Studies have shown that CO2 therapy may help improve athletic performance by reducing vascular inflammation, thereby increasing blood flow. In addition, it may also help protect the body against oxidative stress. Here’s a closer look at how it works.

How CO2 Works in the Body

Completely non-toxic, carbon dioxide exists as a colorless and odorless gas. Inhaling it enables absorption into the bloodstream and circulation throughout the body. Considered “the most ubiquitous hormone of the body,” every cell makes it and has distant actions throughout. The arterial partial pressure of CO2, or PaCO2, defines the level of CO2 in the blood. Depending on the level of PaCO2, different reactions occur in the body.

Hypercapnia (abnormally increased CO2 in the blood) occurs at high levels of PaCO2, which causes dilation (increase in diameter by stretching) of cerebral arteries and arterioles and results in increased blood flow to the brain. This increased blood flow increases oxygen, which can improve cognitive function, plus elevated CO2 levels cause the hemoglobin molecule to release oxygen into the brain or muscle tissue). 

Hypocapnia (below normal CO2 in the blood) occurs at low levels of PaCO2, which causes constriction and therefore decreased blood flow. Worse, without adequate levels of CO2, the hemoglobin molecule cannot efficiently drop or deliver the desired oxygen to the tissues! Typically, many, if not most, athletes hyperventilate (increasing oxygen in the lungs) right before an athletic event or action. This lowers PaCO2 and can lead to reduced reaction speed, spatial awareness, and even lowered cognition (thinking)! In severe cases, lowered PaCO2 can lead to dizziness, anxiety, and even fainting.  

Breathing strategies involving recycling CO2 can help optimize athletic performance by increasing blood flow and oxygen delivery to the tissues. This occurs because hypercapnia initiates a decrease in the affinity of hemoglobin for oxygen, which in turn delivers more oxygen off the transport molecule hemoglobin and delivered to the muscles or brain. Additionally, breathing strategies that involve recycling CO2 regularly in training can help increase the production of 2,3 diphosphoglycerate (DPG), which is an inorganic phosphate helping shift the oxygen dissociation curve to the right, similarly supporting the delivery of more oxygen. DPG is a molecule that helps red blood cells release oxygen to tissues. 

How Athletes Can Use CO2 Recycling Strategies

Roughly 20% of the American population exercise daily (US Bureau of Labor Stats), equating to approximately 24 BILLION new opportunities to enhance one’s exercise and sports physiology yearly. Exercise physiology, the science of how the body responds to physical activity, differs from “sports science,” which defines the science that studies the application of scientific principles and techniques to try to improve sports performance. The latter frames the discussion below shows potential revelations of what CO2 offers to the world. We exhale roughly 4% carbon dioxide (CO2), a colorless and odorless gas. Although completely NON-toxic, does exist as an asphyxiant, meaning it can push other important gases out of the way if it rises too quickly without access to oxygen). Not only does literally every living animal cell produce CO2, but we also know the entire food and biomass of the earth is carbon-based.  Physiologically, the animal kingdom manipulates CO2 in rather dramatic and clever ways. 

Instrumental with more than 20 publications, our research group demonstrated that jugular compression (by way of filling up the compensatory reserve volume [CRV] of the cranium) can, in fact, prevent Traumatic Brain Injury. CO2 also directly fills the CRV by increasing arterial blood flow into the cranium instead of restricting venous jugular outflow. 

We demonstrated this protective physiology in an as-yet-unpublished study by Matthew Robson, Ph.D. (the University of Cincinnati, Department of Pharmacology), while subjecting mice to IED-level blast explosions. The group under study had been exposed to 5% CO2 for only 10 minutes prior to the blast (the control animals were breathing ambient air simultaneously). Notably, the endpoint was a drop in the so-called Righting Reflex Time (RRT), which is the time it takes for the animal to “rise up from being flipped onto their backs.” Dr. Robson explained that he has tested over 100 pharmaceuticals via this FDA-validated study method, and he previously never saw any improvement in the RRT endpoint. With the application of just 10 minutes of CO2 prior to the blast, however, there was a 65% reduction (improvement) in the RRT, suggesting a comparable level of protection to the anatomical structures of the human brain.

Carbon dioxide (CO2) has a profound and reversible effect on cerebral blood flow. Hypercapnia causes dilation, which increases the PaCO2 level and opens cerebral arteries and arterioles, thereby increasing blood flow, whereas hypocapnia (decreased PaCO2) causes constriction, which leads to decreased blood flow., The potent vasodilator (drug causing an increase in vascular openings) effect of CO2 is demonstrated by the finding that in humans, 5% CO2 inhalation causes an increase in cerebral blood flow by 50% and 7% CO2 inhalation causes a 100% increase in cerebral blood flow. , 

Biomimicry (taking inspiration from Nature) may have been overlooked in identifying a physiology to assist athletes, from professionals to novices. Smith et al. have determined that the many highly g-force tolerant creatures manipulate their intracranial volume and pressure to mitigate energy absorption into the cranium to lessen the risk of TBI. Imagine that woodpeckers can tolerate 80 million impacts to their skulls over their lifespans, and most of those impacts are greater than 1200 x g when Man can become concussed with one impact of just 100 x g force.

In 1904, BOHR, HASSELBACH, and KROGH discovered that increased carbon dioxide pressure (PCO2) shifts the oxygen equilibrium curve of blood to the right— in other words, the oxygen affinity of blood is inversely proportional to PCO2. Essentially, this provides more oxygen delivery to the tissues since hemoglobin delivers 98% of the oxygen. Interestingly, modern-day athletes have been known to train at altitude to stimulate the production of DPG, which also shifts the oxygen dissociation curve to the right, similar to increased CO2. 

Specifically, in exercise physiology, CO2 has very specific metrics that pertain to the delivery and management of oxygen, and energy, to the cell’s machinery, thereby optimizing sport. The Bohr-Haldane Effect describes the relationship of the CO2 effect on the hemoglobin framework, allowing the uptake and delivery of oxygen from the lungs to the outer perimeter of the brain and muscles. 

While not a “smart” molecule, the hemoglobin molecule, which carries 98% of all oxygen to the tissues, somehow knows when to attach to oxygen in the lungs and then also knows when to release or deliver that oxygen when it travels into a brain or muscle capillary. Rather, the CO2 level in these respective organs changes the nature of the hemoglobin molecule (low CO2 in lungs and high CO2 in peripheral tissues), which in turn, allows the molecule to “decide” to attach oxygen or expel it into the tissues. Without commensurate high CO2 in the tissues, the body may be able to attach oxygen, but it may falter in knowing where to deliver it.

Historically, there are several ways that athletes can use strategies to enhance their performance. One way is to train at altitude, as indicated above. High altitude exposure decreases oxygen levels during training leading to increased production of DPG and, later, enhanced oxygen delivery to tissues. 

A new study published in the journal Frontiers in Physiology suggests that breathing in carbon dioxide may improve athletic performance. The study’s authors say that the finding could have implications for elite athletes who are looking for any advantage they can get, which gets our attention, BUT what does the science say? Let’s take a closer look.

The Science Behind the Study

The authors used a technique called Intermittent Hypoxic Training (IHT) to test their hypothesis. IHT involves breathing in low oxygen levels for brief periods of time, and it is often used to simulate high-altitude conditions. The authors reasoned that if IHT can help improve athletic performance, perhaps breathing in carbon dioxide—a byproduct of IHT also causing reduced oxygen intake—could also provide benefits.

To test their hypothesis, the authors recruited 12 male cyclists and had them complete four different exercise tests while inhaling either normal air or air that was enriched with carbon dioxide. The tests were designed to measure the cyclists’ anaerobic threshold (AT)—the point at which muscles began to feel fatigued.

The Results of the Study

The results of the study showed that breathing in carbon dioxide improved the cyclists’ AT by an average of 4%. Furthermore, when the cyclists breathed in carbon dioxide during exercise, they perceived their level of effort to be lower than when they were inhaling normal air. In other words, they felt like they were working less hard even though they were pedaling just as fast.

What Does This Mean for Athletes?

While the findings of this study are interesting, it’s important to keep them in perspective. An improvement of 4% in AT is not going to make a huge difference for most athletes. Furthermore, it is unclear whether breathing in carbon dioxide would provide any benefits for activities other than cycling. Therefore, we need more research before we can say definitively that carbon dioxide can improve athletic performance if inhaled during the performance.  Note that we see the key takeaway here: breathing in CO2, even during sport, benefits athletic performance, not hinders it.

But secondly, and potentially more practical, we see increasing interest in a technology allowing one to rebreathe their own CO2 during the “Pre-Performance Period safely,” or right before an athletic event, when forced hyperventilation, increased adrenaline, and heightened body temperatures naturally lead to lowered CO2, just when needed most. Since a lowered CO2 at this precise moment could affect reaction times and spatial awareness, reversing this lowered CO2 should be markedly helpful. Introducing DeltaChase’s newest technology, SAGE Rebreathers,™ has a tagline of “Priming the Pump™” and now awaits human clinical trials to validate our claims.


Athletes tend to follow their own established rituals right before an athletic event, and this curious individualized period has escaped formal investigation until now.  Certainly, many naysayers would expect an added CO2 level to displace oxygen and lower performance, but the opposite actually occurs.  An athlete needs normal, or even elevated, CO2 levels to allow the delivery of oxygen to tissues like the brain and muscles; without it, one should likely see a reduced reaction speed, spatial awareness, and even a potential reduction in cognition power. If you’re looking for an edge in your next competition, consider utilizing CO2 recycling methods!  

Check back to to see when this exciting technology is available.

i Bellis, Mary. “A Brief History of Sports.” ThoughtCo, Feb. 11, 2020,


iii Reivich M. Arterial PCO2 and cerebral hemodynamics. Am J Physiol. 1964; 206: pp. 25–35.

iv Kety SS, Schmidt CF. The effects of altered arterial tensions of carbon dioxide and oxygen on cerebral blood flow and cerebral oxygen consumption of normal young men. J Clin Invest. 1948; 27: pp. 484–492

v Y. Henderson, “Carbon Dioxide,” Cyclopedia of Medicine, 1940

vi The Cerebral Circulation. Cipolla MJ. San Rafael (CA): Morgan & Claypool Life Sciences; Chapter 5, Control of Cerebral Blood Flow, 2009.

vii The Bohr Effect and the Haldane Effect in Human Hemoglobin, Itiro TYUMA, Japanese Journal of Physiology, 34, 205-216, 1984

viii J Appl Physiol 125: 916–922, 2018. First published May 10, 2018; doi:10.1152/japplphysiol.00140.2018