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CARBON MONOXIDEUCIUCI UCI WADAEPOEPO VO2 EPOEPOEPO WADA Your browser does not support the element. is best-known as a poison. Each year around 30,000 people worldwide die from exposure to the gas, which can be produced by cooking stoves or indoor fires. But could it also have something to offer the hard-pressed athlete looking for an edge?The Union Cycliste Internationale (), which governs professional cycling, worries that it might. At a meeting starting on January 31st the will recommend that its bosses ban the use of carbon monoxide by riders “on medical grounds”. The has also asked the World Anti-Doping Agency (), whose rules it has signed up to, to decide whether repeatedly inhaling the gas should be considered doping.There are currently no restrictions on the gas. Indeed, carbon monoxide is routinely used in the peloton to allow teams to keep track of their riders’ fitness. Giving a small dose is the gold-standard way to measure levels of haemoglobin, a molecule found in red blood cells, and an important statistic for endurance athletes. Cyclists including Tadej Pogacar and Jonas Vingegaard, two of the best in the world, have said their teams currently use the gas in this way, which is not against any rules. But last year Escape Collective, a cycling-news website, put the cat amongst the pigeons by suggesting that some teams (it did not name any) might be going further, and using the gas repeatedly to deliberately boost their athletes’ performance.That a poisonous gas might also be performance-enhancing is less surprising than it sounds. Haemoglobin’s job is to bind to oxygen, so that the red blood cells can ferry it around the body. But carbon monoxide binds to haemoglobin more strongly than oxygen does. A red blood cell that is transporting carbon monoxide is one that is not available to move oxygen about. Inhale too much carbon monoxide, and it will asphyxiate you.Inhale a smaller dose, though, and you will merely become mildly oxygen-deprived. If you are oxygen-deprived for long enough, the shortage will stimulate your bone marrow to ramp up the production of red blood cells to try to compensate.That is an attractive proposition for any endurance athlete. More red blood cells mean that their blood can carry more oxygen to their muscles (at least, once the carbon monoxide has worn off). That allows them to run or pedal faster over long distances. The effects of oxygen deprivation are why many athletes spend time at high altitudes, where the air is thinner. When they descend for a race, the hope is that the extra oxygen-carrying capacity of their blood will give them a boost. The same hope underlies the use of the banned drug erythropoietin (). stimulates red-blood cell production directly, and has been a mainstay of doping for more than 30 years. Carbon monoxide theoretically offers similar benefits.It may work in practice, too. In 2020 a group of researchers led by Walter Schmidt at the University of Bayreuth published a paper examining the effects of carbon monoxide on fit amateurs. They found that small doses given five times a day for three weeks—far more than would be necessary for mere monitoring—led to a roughly 5% increase in the amount of haemoglobin in their blood, and a 3% increase in max—a measurement of how much oxygen the body can use and, therefore, an important number in endurance sports.Another paper, published in 2024 by Tomas Urianstad at the University of Inland Norway and his colleagues, found that combining carbon monoxide with altitude training gave a greater boost to some performance markers than did altitude training alone. Any performance increase is probably small, notes Ross Tucker, a sports scientist and keen cyclist, and not comparable to what can be achieved with , “but in conjunction with other things it might be significant.”Even if it is less powerful than , carbon monoxide, were it banned, would offer some advantages to the aspiring doper. Unlike anabolic steroids, which are often used to enhance performance, it is cleared from the body within hours. If it were nonetheless detected in a blood sample there are plenty of environmental sources, from car exhausts to open fires, that could be blamed. (Explaining away a steroid or detection is much more difficult.)Even more appealing, though, is the fact that the gas has legitimate uses. All the equipment and supplies which would be necessary to abuse the gas are already widely used, which means “it would be pretty easy to move the needle from just monitoring to performance enhancement,” notes Dr Tucker. It also means that any attempts to impose restrictions, rather than an outright ban—rules that tried to govern the frequency of inhalation, say—would be hard for the authorities to police. And there is precedent for a ban: in 2014 forbade the use of xenon and argon gas, on the grounds that they had similar benefits to those being claimed for carbon monoxide. (Indeed, sports scientists in Russia had been actively promoting the use of xenon, which was not forbidden at the time.)“For the last two or three years speeds [in cycle races] have been going crazy again,” notes Dr Tucker. That could, he says, be the result of better bikes, or better training, or even better nutrition during a race, which has been the subject of much experimentation in recent years. But cycling’s chequered past leaves a lot of people sceptical. Whether carbon monoxide is the culprit or not, the authorities may decide it is easiest to forbid it altogether.
