How do Tour de France riders adapt to the heat?

Racing the Tour de France is very hard work. It's a fact I occasionally forget sat watching the spectacle on telly, as riders effortlessly scale hills at over 20kph, shooting past idyllic green pastures under wide open skies. But at home I’m protected from one, integral thing: beating down through those azul skies is a big, hot sun.

With temperatures peaking at 40 degrees in recent Tours de France, riders have to contend not only with mountain climbs and flat-out race days, but scorching temperatures and its effects on the body, too.

“When your body starts to heat up, the blood flow gets taken towards the skin,” Dr Lindsey Hunt, of Precision Fuel and Hydration tells me.

“Our skin temperature gets very hot, and that leaves less blood in the central system - in our heart and in our muscles - so our heart rate has to go up to maintain blood pressure.”

Exercising in hot temperatures without adequate training and "pre-loading" of liquids can be dangerous. As we get hot, we loose moisture through the skin excreted as sweat. This increases our sodium levels, which in turn triggers our thirst responses. If you loose too much liquid and don't rehydrate in time, your performance could be impacted, or more seriously, lead to heat stroke.

It is likely that the Tour competitors will be contending with some hot weather on race days. So far 2025 has produced another record breaking summer. In the lead-up to the French Grand Tour, which is set to start this Saturday, nation-wide weather warnings swept France, closing nearly 200 schools and sparking forest fires in the southern Corbières mountain range.

What does this mean for the Tour? Well, depending on just how hot the race may get, stages could be tweaked, resulting in shadier start lines. In all likelihood however, the race will go on undeterred, but closely monitored by a team of race organisers, UCI and rider representatives ready to make on-the-day judgements of race safety in line with the UCI’s High Temperature Protocol.

However, luck seems to be on the side of the Tour contenders this year. Beginning in the north of France, Saturday’s first stage in Lille will be a balmy 25 degrees as riders set off on 184.9km from 1 - 5pm. As the race moves from West to South, snaking through the country’s heartland via Chateauroux and down into Toulouse for stage 11 on 16 July temperatures will inevitably rise.

So, how can riders stay cool during races?

Ice packs will be shoved into jersey collars and water tanks may be in use to douse the peloton in cooling sprays, all aided by blocks of pre-race heat-training.

“Riders will go to hot environments, and train outside in the heat,” Dr Hunt explains.

“They could also train in a set up at home, like a conservatory or a garage with heaters and that sort of thing. Or the other way - which is becoming popular - is wearing a heat suit or additional layers of clothing on the indoor trainer.

"This could be something that some of the Tour riders are doing this week, where they're looking to maintain their sweating response but don't want to necessarily be training on the bike in the heat - it's kind of a lightweight version."

Heat training is a way to prompt physiological changes in the body. It can increase sweat rates, which works to move heat away from the body more quickly, as well as increasing the levels of blood plasma needed to help the body self-cool.

"But at this point, just under a week before the Tour, they're probably not doing too much heat prep. A lot of that preparation has been done in the lead up to the race, [and now] they're just going to be focusing on good hydration practices to make sure they're not getting dehydrated in this recovery period pre-race.”

Heat training is effective. Even with short heat training sessions of under seven days, studies show that the body can begin to better regulate temperature changes, increasing in performance with longer stints of training, ideally between 8-14 days.

However, for those of us not racing the Tour this year, but who are wanting to get out on some longer, hotter rides, Precision Fuel and Hydration's CEO Andy Blow’s advice is to hydrate well, and to use electrolytes.

"The body is really, really good at adapting to the heat if you give it the stimulus," he tells me. So why not give it a go?

Oh, and try hopping into the sauna for some short heat training sessions - apparently they're popular with the pros.