On Saturday 17 August this year, some of the world’s best cyclists started the Vuelta a España, which began in Portugal and will be navigating its way around Spain to the finish line in Madrid on Sunday 8 September. Hopes that road cycling’s superstar Tadej Pogačar would look to add the Vuelta title to his 2024 Giro d’Italia and Tour de France triumphs, and become the first rider to win all three of the sport’s “grand tours” in the same season, were ended at the end of July when the Slovenian opted to skip the Paris Olympics and the three-week Spanish stage race to prepare for the road cycling world championships in September. That was the diplomatic pronouncement.
On the Geraint Thomas Cycling Club podcast, the Welsh cyclist revealed: “I asked him in the peloton and he said, ‘I need to keep people in the team happy. We have so many key riders at UAE Team Emirates. I understand that.’” Meaning the likes of Britain’s Adam Yates and Portugal’s João Almeida would take centre stage. And meaning they might be the ones fielding further questions on the controversial but legal carbon monoxide rebreathing method – a measurement tool that enables athletes to monitor key blood values such as haemoglobin levels – that came to light at this year’s Tour de France.
“Carbon monoxide rebreathing is a method to assess total haemoglobin mass and has been used in altitude training and research for over 20 years,” a statement from UAE said. “It is a well-established, safe, professional method that is backed by a very large amount of research.”
What is less well established and less widely known is that research suggests that frequent use of the diagnostic devices can improve a rider’s endurance capacity, as well as assess it. There is no evidence of WorldTour teams using it for these purposes, but that didn’t stop French sports newspaper L’Équipe running with the headline “A domination that raises questions”, three days after Pogačar had smashed the late Marco Pantani’s tarnished 1998 record Tour ascent of the Plateau de Beille by an estimated three minutes and 40 seconds. (Pantani was later found by the French senate to have taken the blood-boosting and banned hormone erythropoietin (EPO)). Those L’Équipe questions included the use of the carbon monoxide rebreathing method.
US-based cycling website Escape Collective had earlier reported that UAE Team Emirates, Visma-Lease a Bike and Chris Froome’s Israel-Premier Tech had all used the method, though each team stressed that they had used it purely for testing purposes. The practice isn’t banned by Wada (the World Anti-Doping Agency) as, in small doses, it’s used to measure blood parameters, both medically and in the sporting sphere.
“Haemoglobin mass is one of the greatest predictors of endurance exercise performance,” says Carsten Lundby, professor of integrative exercise physiology at the University of Southern Denmark and chief executive of Detalo, which makes the gold-standard Detalo rebreathing devices. “It’s valuable for cyclists to design exercise training strategies that may increase haemoglobin mass and hence exercise performance. These could include high-altitude and heat-training sessions. In order to optimise these, the precise assessment of these blood variables is essential.”
Lundby explains how the device works: “A very small and very accurate bolus of carbon monoxide is inhaled. At the same time oxygen is added. After a few minutes of rebreathing this mix, a small blood sample is obtained and analysed for carbon monoxide content. This then allows the determination of haemoglobin mass plus plasma and red-blood-cell volume. It’s the only device of this kind approved for human use.”
This differs from a regular blood test you or I might have undertaken, Lundby adds, which only provides haemoglobin concentration and not total haemoglobin mass or total blood volume.
Taking a rebreathing test raises the carbon monoxide level in your blood to just under 6%, says Lundby. You would go about your normal day with levels of about 0.5% just from exhausts and pollution, while a smoker’s is about 8%. For a normal adult, after a rebreathing test levels would be at 2% by the next morning and back to normal within the day, even quicker if you exercise during that time.
The method was first developed in 1960 by eminent researchers, says Lundby, and has been used extensively ever since. He’s worked with “numerous WorldTour riders and many world champions and Olympians and Olympic institutions” to assess haemoglobin mass. “There is absolutely nothing new to it,” he says.
Frequency equals faster cycling
Not in a measuring sense. It’s also not dangerous. Again, in the quantities required to measure those blood changes. The potential problems – not to say dangers – and the reason the topic of carbon monoxide has gained traction – is its potential to enhance performance.
Before the grand départ of the Tour de France from Florence, Italy, I’d attended the Science and Cycling conference in the city, and a presentation by Daniele Cardinale, head of the sport physiology and performance laboratory at the department of elite sport support at the Swedish Sports Confederation. “Going to altitude isn’t always practical, especially during Covid,” he said. “Is there another way? That’s when I came across carbon monoxide. It originally scared me because you associate it with danger, [with] poisoning.”
Cardinale explained how carbon monoxide binds to haemoglobin with 240 times the affinity of oxygen to form carboxyhaemoglobin. It takes several hours to dissociate from haemoglobin, during which time the oxygen-carrying capacity of blood is lowered. This, said Cardinale, resulted in a surge of EPO similar to that enjoyed by riders at altitude. This led to an increase in haemoglobin mass and performance. He’d shown it in a yet to be published study.
Exercise physiologist Dr Jamie Pringle, who set up laboratories at the English Institute of Sport with this capability in about 2009-10 and has a number of research projects in progress at University of Birmingham into rebreathing, says despite Wada’s allowance of carbon monoxide, its performance-enhancing benefits are known. “It’s a few years since Walter Schmidt’s paper came out and it’s been a concept for much longer,” he says.
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Schmidt’s noteworthy 2020 experiment had 11 subjects inhale carbon monoxide five times a day for three weeks, whereby their haemoglobin mass increased by 5%. Similar to Cardinale’s study, this increase was accompanied by a measurable increase in endurance performance and corresponded to the effects of an altitude training camp over the same length of time.
When contacted by the Observer, UAE Team Emirates, Israel-Premier Tech and Visma-Lease a Bike referred us to statements they had made during the Tour de France and to the Escape Collective that acknowledged their use of carbon monoxide rebreathing for measurement purposes only.
In statements, UAE Team Emirates has confirmed that it is a diagnostic tool not a therapeutic one, while Israel-Premier Tech’s team statement suggested the sole use of the Detalo blood volume analyser was for test purposes, to measure the impact of altitude.
The teams did not elaborate on the minutiae of their test protocols, although Mathieu Heijboer, head of performance at Visma-Lease a Bike, told Escape Collective that they had been working with Bent Rønnestad for several years. Rønnestad, a professor at the Inland University of Norway and an expert on altitude physiology, measures the riders’ haemoglobin mass levels at the start and end of an altitude camp. Israel-Premier Tech uses a machine at Tel Aviv University Sylvan Adams Sports Institute and testing is supervised by Lundby, who told Escape Collective that the machines are used for measurement purposes only.
Lundby told the Observer he views the publication of the Schmidt study as an “unfortunate twist” since unscrupulous athletes and amateurs might attempt to follow the protocol using “crude home-made equipment”, which could result in “doses that are outright lethal”.
A history of pushing the limits
Key to the boost in endurance performance that Schmidt discovered is frequency, with carbon-monoxide top-ups required every four hours, day and night, to elicit an effect on performance. It raises the question: would an athlete really inhale large amounts of a toxic gas in search of optimum performance?
Ask yourself another question and you might have the answer. Would athletes extract blood and pop the blood bag in a fridge or freezer for reinfusion when their current levels had returned to normal? Would they self-inject a synthetic hormone, again to increase red-blood-cell count? Would they risk thickening blood that could lead to death in search of a competitive edge? History provides the answer.
In the wrong hands, severe illness and potential death is the doomsday scenario. But as it stands, inhalation of carbon monoxide is not on Wada’s prohibited list, even at high levels. “Exposure to carbon monoxide has been discussed by Wada’s prohibited list expert advisory group, but there is no consensus on whether it can have a performance-enhancing effect, and no sufficiently robust data currently supports that proposition,” Wada told us. “It is, however, generally acknowledged that it can be dangerous to use, so it would not be recommended.”
Pringle suggests that controversy over inhaling a poisonous gas will mean chronic carbon-monoxide inhalation (several inhalations a day) will almost certainly be banned by Wada in the coming months. “I think that’s inevitable because it can only ever be regarded as ‘harmful to the health of the athlete’, which I don’t think anyone could argue otherwise.”
“That inevitable banning is also down to precedent,” Pringle adds. “Gases like xenon and argon, which are used for the exact same purposes of reducing the oxygen-binding to haemoglobin and stimulating erythropoiesis, were banned by Wada 10 years ago. It was a practice that came to light with the Russians before it was banned, but really came to light at the 2014 Sochi Winter Olympics.” In Sochi, many Russian athletes admitted inhaling the then legal substance xenon in pursuit of gold.
After contentious US claims that Wada covered up previously undisclosed cases of Chinese swimmers testing positive for a banned steroid in 2021, you suspect the agency will not want to let the performance-enhancing fumes of carbon monoxide cloud its credibility further by allowing its chronic use. Whether that will have the desired effect on unethical athletes and coaches seeking a dangerous shift in performance remains to be seen.