You may have caught a few headlines during this year’s Tour de France about riders inhaling carbon monoxide (CO) on purpose to prepare for the mountains. It sounds like science fiction, and it may call to mind the image of a bunch of riders in the team bus huffing from helium-filled balloons and delivering their post-race Instagram story recaps in high-pitched voices. However, it is a very real technology that some teams are using to be better prepared for altitude. Is there a chance it could be misused? Possibly. Is it going to be banned? Not anytime soon.

What Is a Carbon Monoxide Rebreather?

A carbon monoxide rebreather is a device some cycling teams use to help their riders adapt to altitude training. It works by administering a precise dose of carbon monoxide to the lungs, which allows doctors and coaches to measure critical blood metrics, particularly hemoglobin levels. This helps evaluate how well the riders respond to training at different altitudes.

The Escape Collective was the first to report on the use of these carbon monoxide rebreathers, with three teams—UAE Team Emirates, Visma-Lease a Bike, and Premier Tech—confirming their usage. The devices aren’t meant to force riders to suck in carbon monoxide in huge amounts; rather, the device uses a precise dose of carbon monoxide in the lungs in order to capture key blood metrics that would allow team doctors and coaches to see how riders are adapting to certain altitude protocols.

“There is nothing suspicious about it.”

Will the UCI Ban Carbon Monoxide Rebreathers?

It’s worth noting that in this case, the measurements themselves are arguably where the gains are being made—and that’s something the UCI has typically frowned upon. Remember when UCI president David Lappartient wanted to ban power meters in racing? Or a couple of years ago when the UCI did, in fact, ban continuous glucose monitors (CGMs) in competition? A power meter and a CGM don’t do anything—they just measure so riders can manage. So, while Vingegaard points out that taking the measurement isn’t enhancing performance in any way, it’s easy to see a world where this tech gets banned. Or, if it doesn’t, it may very well bring back up the case for allowing CGMs and other similar devices in competition.

A reported 12 teams in the Pro Tour are using these devices, and the Movement for Credible Cycling (MPCC) has said they have no intention of calling for a ban on them. Currently, its use is allowed under the World Anti-Doping Agency (WADA).

The worry is that beyond using the device for testing, some teams and riders will use it in a more extreme way, opting for carbon monoxide inhalation rather than the testing protocols. Technically, even this usage isn’t banned by WADA, though it exists in a gray area since carbon monoxide can cause changes in the blood—something that is, in fact, banned. The Escape Collective report noted that teams may be able to use these carbon monoxide inhalation protocols to achieve the same effects as altitude training.

Riders, including Vingegaard and Tour de France winner Tadej Pogačar, along with their teams, admitted to using the tech for testing purposes. But with their stunningly fast performances on the mountain stages of this year’s Tour, naturally, some eyebrows were raised. At first, Pogačar avoided answering a reporter’s question about his use of the carbon monoxide rebreather, but the next day, he addressed it, saying that he used it at his altitude camp for testing purposes. He added, “It’s not like we’re breathing exhaust pipes every day in the cars. It’s just a pretty simple test to see how you respond to altitude training.”

Naturally, plenty of former pros weighed in on the growing controversy, with (ugh) L.ance Armstrong offering words of ‘wisdom’ to Pogačar and suggesting he ‘lay low’ rather than attacking in such bold ways. Bernard Hinault was on Team Pogačar, saying, “I am disgusted… Why do we always express doubts?” when writing about the—ahem—COntroversy.

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