Sports health
The surprising performance enhancing substance that can be lethal
While there may be some benefits, athletes are being warned of the associated risks, which can be fatal.
In the high-stakes world of professional cycling, athletes are constantly seeking ways to enhance their performance. One unconventional method gaining attention involves the controlled inhalation of carbon monoxide (CO). According to Dr. Iker García Alday, a 31-year-old physiology professor at Escola Vitae affiliated with Universitat Abat Oliba CEU and an exercise physiology researcher in Logroño, Spain, precise doses of CO can boost athletic performance. However, high doses can be fatal.
This practice has stirred debate among cyclists, including prominent figures like Tadej Pogacar and Jonas Vingegaard. While the World Anti-Doping Agency (WADA) investigates the implications, the Movement for Credible Cycling (MPCC), representing eight WorldTeams and 385 cyclists, has recently opposed CO inhalation. In a statement, the MPCC cited the potentially lethal health risks, the technical and artificial nature of the method, and existing anti-doping codes as reasons to strongly discourage its use until it is officially banned.
During the recent Tour de France, reports emerged of leading teams such as UAE and Visma employing CO breathing techniques, leading to skepticism in some circles. When questioned, cyclists like Pogacar and Vingegaard defended the method, emphasizing its role in assessing training efficiency rather than directly enhancing performance.
French cyclist Romain Bardet voiced his concerns, describing a “arms race” among teams to adopt the most advanced performance-enhancing mechanisms.
Beware: the lethal potential of carbon monoxide
“Carbon monoxide is an odorless and colorless gas resulting from incomplete carbon combustion. When inhaled in high doses, it is lethal, but at very low doses, it serves as a physiological signal that modulates processes like inflammation and oxidative stress. It’s present in our atmosphere; we coexist with it,” Dr. García explained to EFE.
He detailed, “Carbon monoxide has a 200-fold higher affinity for hemoglobin than oxygen. This property is utilized in various medical tests at very low doses to measure health parameters such as pulmonary diffusion and total hemoglobin.”
However, in uncontrolled environments, red blood cells' hemoglobin binds to carbon monoxide instead of oxygen, posing a life-threatening risk.
Balancing risks and benefits
“In sports, using low doses of carbon monoxide is common for measuring hemoglobin levels – the protein responsible for oxygen transport in blood. Teams with the means often use this practice in altitude training to assess improvements,” García Alday clarified.
He noted that studies over the past five years have shown that repeatedly inhaling low doses of CO (around 1% of the air breathed) for 10-minute sessions, one to five times daily, can increase hemoglobin levels by 5%, similar to training at high altitudes.
When inhaled once daily before training, CO binding to hemoglobin reduces oxygen transport, mimicking hypoxia from altitude. “This signals the kidneys to secrete the hormone EPO, which increases red blood cells in the blood,” the specialist added.
The primary risk lies in misuse and neurological effects, but moderate doses can elevate cardiovascular stress and heart rate, cause nausea or vomiting, and higher doses may lead to fatal poisoning.
The benefits include increased hemoglobin to transport more oxygen to muscles, thereby enhancing aerobic performance. García Alday referenced the precedent set by noble gases like argon and xenon, used in 2014 and subsequently banned by WADA. “Now, the concentration is much lower, but risks remain. The line between doping and technological enhancements is narrowing.”
It’s important to note that CO use “offers no benefits during actual competition,” as the gas has a half-life of about 12 hours, reducing oxygen transport capacity to muscles. The reported benefits are comparable to those of altitude training.
A comparable alternative to high-altitude training
From a sports preparation perspective, inhaling CO for 10 minutes daily over three weeks appears to yield similar benefits to spending three weeks training at high altitude in the Sierra Nevada, without the need to travel or be away from family.
“Carbon monoxide inhalation can prolong or even replace the benefits of altitude training. Creating artificial hypoxia through appropriate doses of inhaled CO mimics the effects of altitude exercise,” García concluded, but the warning couldn’t be clearer.
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