ANALYSIS: Carbon monoxide is the latest wake up call for cycling, but how many more can the sport survive?

Cycling’s long and complex relationship with performance enhancement has taken another turn with the UCI officially announcing earlier this month that they are banning carbon monoxide (CO) rebreathing in the peloton. The decision, which came into effect on February 10, 2025, has been one of the most debated topics in the sport over recent months.

Unlike previous cases of banned substances or doping products, carbon monoxide rebreathing sat in a grey area, one that was controversial but never illegal. Let’s face it, a cycling ‘grey area’ is always going to set off alarm bells for most fans, and the call to ban the use of carbon monoxide was the right call.

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But the ban raises broader questions about how cycling regulates emerging performance-enhancing techniques, the ethics of marginal gains, and whether the sport is capable of fully moving beyond its dark past. If cycling is to learn from this saga, it must address why CO rebreathing became widespread, why it took so long to regulate, and how future grey areas should be handled.

Let’s dive into what is a dark, complicated, and confusing situation that embodies a lot of the struggles cycling still faces in overcoming it’s blemished record.

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Why did riders start using carbon monoxide

Performance. That’s why the riders started using it, and performance is the reason for the vast majority of things cyclists do, everything is geared to maximise their performance on race day.

The science behind carbon monoxide rebreathing is complex, but its fundamental appeal is simple: it increases a rider’s total haemoglobin (Hb) mass, enhancing their ability to transport oxygen through the bloodstream. More oxygen means better endurance, improved recovery, and greater resistance to fatigue, all critical in a sport where the margins between winning and losing are razor-thin.

Traditionally, riders looking to increase red blood cell production have relied on altitude training or hypoxic chambers, which simulate high-altitude conditions to stimulate natural adaptations. Carbon monoxide rebreathing offered a shortcut, allowing riders to achieve similar benefits in far less time.

Tadej Pogacar and Jonas Vingegaard came under scrutiny for their use of carbon monoxide

With riders at the very pinnacle of the sport, such as Tadej Pogacar and Jonas Vingegaard, linked to its use, the method gained traction in professional cycling. However, what made CO rebreathing so controversial was not just its effectiveness, it was the serious health risks that came with it.

Why was the ban necessary?

The UCI has made it clear that its decision was based on protecting rider health, not necessarily concerns over performance enhancement. Unlike traditional doping methods, which focus on unfair advantages, CO rebreathing presented a direct and immediate risk to those using it.

Carbon monoxide is a toxic gas. While it is used in controlled medical settings, repeated exposure can lead to headaches, dizziness, nausea, confusion, and, in more severe cases, heart problems, seizures, and even paralysis. The potential for long-term damage made this method far more dangerous than traditional altitude training, which relies on natural adaptation rather than chemical manipulation.

The word natural is crucial here, and perhaps it is crucial in the wider debate in what is ethical from a sporting perspective in terms of gaining performance. Is anything ‘unnatural,’ really supposed to be used by the riders?

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The UCI’s statement emphasised that repeated exposure could lead to chronic health conditions. Unlike other performance-enhancing techniques, which primarily raise ethical or sporting concerns, CO rebreathing posed a direct danger to the athletes using it.

The sport has a history of riders pushing their bodies to the absolute limit, often disregarding their long-term health in pursuit of success. This ban forces cycling to confront a difficult reality: when performance gains outweigh personal safety, the governing body must step in. The UCI has taken that step, but should it have acted sooner?

The need for clearer rules

One of the most perplexing aspects of the CO rebreathing controversy was that it was never explicitly illegal before this ban. Riders and teams were operating within a grey area, exploiting the lack of regulation to gain an edge without breaking any formal anti-doping rules.

And teams have and will always do this, not just in cycling but throughout all sport. Find a way to bend the rules, or a grey area, and use it to their advantage.

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This raises a fundamental issue: how should cycling handle new performance-enhancing techniques that do not fit neatly into existing doping definitions? The World Anti-Doping Agency (WADA) had not yet banned CO rebreathing, and until now, the UCI had no clear regulations against its use.

By taking independent action, the UCI has set a precedent that could shape how future performance-enhancing methods are handled. But this case exposes a wider problem in cycling’s regulatory approach: the sport often reacts after the damage has been done rather than proactively addressing emerging issues.

This is not a new problem for cycling. The sport has a long history of being slow to regulate new practices, allowing controversial methods to spread before eventually banning them. Whether it was blood transfusions in the 1990s, EPO abuse in the 2000s, or the use of tramadol more recently, the pattern remains the same, riders take advantage of a loophole, and only when public pressure mounts do the authorities step in.

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This reactive approach damages cycling’s credibility. How many other performance-enhancing techniques are currently being used that sit in similar grey areas? What happens when another questionable method emerges? The UCI’s ban on CO rebreathing is necessary, but the sport must develop a more structured way to address these issues as this dark cloud continues to hold cycling back.

The paradox of marginal gains

CO rebreathing is just another example of the constant search for marginal gains in professional cycling. Every era has seen teams push the boundaries of what is acceptable, sometimes within the rules, sometimes well beyond them.

Cycling has always operated in a culture where small advantages can make the difference between winning and losing. This has led to cutting-edge innovations but also to widespread abuses. In a sport where races are decided by fractions of a second, teams will always explore new ways to push the limits.

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For the most part, marginal gains help to make cycling the sport we love. Riders pushing themselves to the limit of their ability, pushing themselves beyond what they thought was possible, to gain that tiny 1% extra.

The question is: where does cycling draw the line?

The problem is not just about CO rebreathing but about how the sport defines what is acceptable and what is not. If CO rebreathing was banned because of health concerns, what about other questionable medical practices that might not be as extreme but still present risks? The case of CO rebreathing suggests that cycling lacks a coherent philosophy on performance enhancement.

If the sport truly wants to move forward, it must stop waiting for controversy to force change and instead develop clear guidelines for emerging training methods before they become problems.

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There are several lessons cycling must take from this episode if it is to avoid repeating the same mistakes in the future. The first is that unclear rules create loopholes. Riders and teams will always take advantage of unregulated grey areas if they believe it will provide a competitive edge, and the only way to prevent this is for governing bodies to act pre-emptively, identifying new training methods before they become widespread.

From the very dawn of doping within sport, that has always be the headache the governing bodies face: the cheats (or in this case those in the grey are) are always one step ahead.

The second lesson is that health must be prioritised over performance gains. The fact that riders were willing to inhale a toxic gas to improve their endurance should be alarming, and it raises serious ethical and moral questions over how far teams and riders are willing to push themselves. If marginal gains outweigh personal well-being, the sport has a deeper issue that needs to be addressed.

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The third and perhaps most important lesson is that cycling cannot afford to keep repeating its past mistakes. The sport has fought long and hard to move beyond the doping scandals of the 1990s and 2000s, yet time and time again, it finds itself entangled in new controversies. If cycling is serious about cleaning up its image, it must implement a proactive regulatory framework rather than continuing this cycle of controversy and delayed action.

The UCI’s decision to ban carbon monoxide rebreathing is an important step, but it is only one part of a much larger problem. Cycling has long struggled to balance innovation with ethics, and as long as teams continue searching for new competitive advantages, controversial methods will keep appearing.

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This latest controversy should serve as a wake-up call, as if cycling hasn’t had enough of them already! The sport must be clearer in its rules, faster in its responses, and more proactive in protecting riders. If cycling fails to learn from this episode, it will only be a matter of time before the next grey-area controversy emerges.

The ban may stop the carbon monoxide debate, but cycling’s larger fight with performance enhancement is far from over.

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