Cathal Dennehy: Carbon monoxide inhalation the latest marginal gain in pro cycling

The practice is perfectly legal but that is likely to change, and there’s a clear precedent when it comes to athletes inhaling small amounts of potentially deadly gases.

The peloton cycles past the Serre Poncon lake during the 18th stage of the 111th edition of the Tour de France. Picture: THOMAS SAMSON/AFP via Getty Images

Carbon monoxide, we’ve long been told, is a silent killer. But if you’re an elite endurance athlete who trains at altitude and is trying to squeeze out a performance edge, it might just lead to a better performance. No, really.

Now, before we’re accused of promoting a potentially deadly practice, let’s be clear: this is not to be tried at home. Now that that bit of ass-covering is out of the way, here’s the deal on the latest marginal gain that’s said to be rising in popularity among pro cyclists.