In 2024, the biggest news in the world of cycling doping sounded like an April Fool’s joke. Pro riders were apparently inhaling carbon monoxide to boost performance. That sounds preposterous until you realize that carbon monoxide rebreathing can be used as a measurement tool to measure a rider’s hemoglobin (Hb) mass and blood volume.
But as first reported by The Escape Collective, it is possible to misuse this test equipment to go from simply testing your Hb mass to improving it with prolonged inhalation. TrainingPeaks has an in-depth article on the science behind CO Hb testing here, but the short of it goes like this:
“First, an athlete typically does a combination of breath and blood tests to measure their baseline carbon monoxide (CO) levels before the actual test is performed.
The test itself involves the athlete inhaling a small amount of carbon monoxide diluted with oxygen. This mixture is inhaled and exhaled through a closed circuit for two minutes. The carbon monoxide the athlete inhales then binds to the hemoglobin in red blood cells to form carboxyhemoglobin.
After two minutes, the amount of carboxyhemoglobin that remains in the breath and blood is re-measured and compared to the baseline levels measured at the start of the test. The results are then used to calculate the athlete’s total hemoglobin mass.”
That testing can then be used to assess an athlete’s altitude adaptation, but it could also be abused if an athlete were to “frequently inhale the tracer to simulate hypoxia and prompt an increase in hemoglobin and other performance metrics.”
That’s where the UCI is attempting to draw the line with their latest ban. Calling it “a ban on repeated inhalation of carbon monoxide,” the UCI will still permit one CO inhalation to measure total Hb mass. Or two, apparently, stating “The inhalation of CO will remain authorised within a medical facility and under the responsibility of a medical professional experienced in the manipulation of this gas for medical reasons and in line with the following restrictions: only one CO inhalation to measure total Hb mass will be permitted. A second CO inhalation will only be authorised two weeks after the initial Hb measurement.”
For more details, check out the full press release below which also includes a modification for UCI WorldTeams to remain eligible.
The Management Committee of the Union Cycliste Internationale (UCI) met in Arras (France) on 31 January and 1st February, alongside the 2025 UCI Cyclo-cross World Championships, which are being held in Liévin from 31 January to 2 February.
To protect the health of riders, the UCI Management Committee approved a ban on the repeated inhalation of carbon monoxide (CO). The ban will come into force on 10 February 2025.
As a reminder, CO is commonly used in sports medicine to measure total haemoglobin (Hb) mass and blood volume, especially to examine the effects of endurance training and altitude exposure on oxygen carrying capacity. However, its repeated inhalation can result in acute and chronic health problems, for example headaches, lethargy, nausea, dizziness, and confusion. Such symptoms can worsen at any time and develop into problems with heart rhythm, seizures, paralysis, and loss of consciousness.
The new regulation forbids the possession, outside a medical facility, of commercially available CO re-breathing systems connected to oxygen and CO cylinders. This ban applies to all licence-holders, teams and/or bodies subject to the UCI Regulations and to anyone else who might possess such equipment on behalf of riders or teams.
The inhalation of CO will remain authorised within a medical facility and under the responsibility of a medical professional experienced in the manipulation of this gas for medical reasons and in line with the following restrictions: only one CO inhalation to measure total Hb mass will be permitted. A second CO inhalation will only be authorised two weeks after the initial Hb measurement.
For riders in UCI WorldTeams, UCI Women’s WorldTeams and UCI ProTeams, any CO inhalation for the purpose of determining total Hb mass must be recorded in the medical file established for each athlete, in compliance with Articles 13.3.020 to 13.3.026 of the UCI Medical Rules.
The UCI’s ban is independent of the World Anti-Doping Code and the UCI Anti-doping Regulations, however the UCI has officially requested the World Anti-Doping Agency (WADA) to take position on the repeated use of CO in and out of competition.
With the aim of ensuring the participation of the world’s best teams in all the most prestigious road events, the UCI Management Committee approved a modification to the participation rules for the UCI WorldTour and UCI Women’s WorldTourfrom 2026.
Under this new rule, it will be mandatory for all UCI WorldTeams to compete in the three Grand Tours (Giro d’Italia, Tour de France and La Vuelta Ciclista a España) and the five Monuments (Milano-Sanremo, Ronde van Vlaanderen, Paris-Roubaix, Liège-Bastogne-Liège, and Il Lombardia). From the remaining events on the UCI WorldTour calendar, UCI WorldTeams will be able to choose one event in which they do not compete. No more than four UCI WorldTeams may be absent from the same event, and teams will not be permitted to be absent from the same event more than once during the three-year registration cycle (2026-2028). Any spot at a UCI WorldTour event left vacant by one of the 18 UCI WorldTeams will be offered by invitation to a UCI ProTeam.
The same participation rules will apply to UCI Women’s WorldTeams in the UCI Women’s WorldTour, but only for the following events: the Vuelta España Femenina by Carrefour.es, Giro d’Italia Women and Tour de France Femmes avec Zwift.
Regarding other disciplines, the UCI Management Committee approved the award of the 2025 UCI Indoor Cycling World Championships to Göppingen, Germany, from 7 to 9 Novembers 2025.
Members of the UCI Management Committee also approved the following calendars:
- 2025-2026 UCI Cyclo-cross International Calendar, including the 2025-2026 UCI Cyclo-cross World Cup;
- 2025 Hero UCI Cross-country Marathon World Cup, a new independent series for the mountain bike marathon speciality which will no longer be part of the WHOOP UCI Mountain Bike World Series;
- 2025 UCI Mountain Bike Eliminator World Cup powered by citymountainbike.com.
These calendars will be available on the dedicated section of the UCI website from 3 February.
Finally, the Management Committee expressed its appreciation of the excellent work carried out in all regions of the world by cycling’s five Continental Confederations, which hold their elective Congresses this year. Congratulations went to Tony Mitchell who, following the Congress of the Oceania Cycling Confederation in January, embarks on another four-year term as its President. The Cycling Confederations of Africa, America, Asia, and Europe will elect their Presidents and Management Committee members at their respective Congresses taking place between now and the beginning of March.
UCI President David Lappartient said: “The UCI takes a bold and necessary stance by banning the repeated use of carbon monoxide inhalation on medical grounds. Our priority is to protect the health and safety of our athletes and today’s decision is another significant step in this direction.
“By modifying the participation rules for the UCI WorldTour and UCI Women’s WorldTour, organisers, riders and fans can be sure that all events in these two leading series for men’s and women’s professional road cycling will feature the best teams in the world.
“Finally, I would like to sincerely thank and congratulate the five Continental Confederations that work tirelessly to progress our sport in all corners of the world. This year marks the start of a new four-year term for the Direction of each Confederation, and I look forward to continuing our excellent and close collaboration.”
The next meeting of the UCI Management Committee will take place in Arzon, France, from 10 to 11 June 2025.
