The Tour de France should consider major changes to avoid the worst effects of heat stress on its riders, according to climate researchers.
The current format and schedule is “becoming questionable”, they told The National.
The study, published in Scientific Reports, analysed climate data associated with 50 Tour de France cycle races from 1974 to 2023.
The research was led by the French National Research Institute for Sustainable Development (IRD), London School of Hygiene & Tropical Medicine (LSHTM) and the Barcelona Institute for Global Health (ISGlobal).
The research team retrieved historical meteorological records for 12 locations frequently visited by the Tour de France, as well as for all July dates corresponding to the different editions of the race.
Its conclusions apply to any sporting event held in summer in Europe or in other regions facing high heat stress risk. “Many sports federations already have their own protocols in place – Fifa, for example, introduced hydration breaks in football. The issue is that temperatures have not yet peaked, and they threaten not only the Tour, but also the Olympic Games and the Football World Cup. It is time to sit down, conduct sport-specific research and make bold decisions,” they said.
But the Tour is their greatest concern, which this year takes place from July 4 to 26, at peak summer season. Separate data showed the first stage of the Tour in 2024 showed temperatures reached 40ºC.
“Extreme heat is closing in on the race to the point where its current format and timing are becoming questionable, due to the high risk of heat stress this would pose for cyclists, teams and the general public,” they wrote.
Teams carry out their own physiological data on riders and help riders acclimatise to the heat through training in enhanced heat conditions. Riders also eat ice gels during races to cool down.
Ivana Cvijanovic, researcher at IRD and first author of the study, called on Tour teams to provide anonymous data of riders so they can be studied independently for the effects of heat stress.
She warns that metrics for calculating risk are outdated and were based on occupational health standards for people at work, not elite athletes. She also points out that individual data would be useful as the risk threshold is not the same for each person. She is particularly concerned that this year’s race has a stage in Barcelona.
It is not just temperature which is taken into account, but also issues such as humidity and wind factor.
The most recent decade accumulated the highest number of extreme heat days, although the Tour has so far managed avoid conditions of maximum health risk, in some cases by only a matter of days or tenths of a degree. Researchers say this has been down to good fortune as races are planned long before weather forecasts are known. They warn Paris and Lyon could become new heat stress hotspots.
“The city of Paris, for example, has crossed the high-risk threshold for heat on five occasions in July, four of them since 2014,” said Ms Cvijanovic. “Other cities have experienced many days of extreme heat in July, but thankfully not on the date of a Tour de France stage.”
She said it would be naive to assume that this good fortune will continue for another five decades. “In a way, we can say that it is an extremely fortunate race, but with record-breaking heatwaves becoming more frequent, it is only a matter of time before the Tour encounters an extreme heat stress day that will test existing safety protocols,” she added.
However, the most dangerous heat levels were most common around Toulouse, Pau and Bordeaux in southwestern France, and around Nimes and Perpignan in the south-east.
In the study data it was found Paris had reached 28.8C in 2019, Nimes reached 30C in 2020 and Bordeaux 301 C in 2019.
By contrast, classic mountain stage locations such as the Col du Tourmalet and Alpe d’Huez have historically remained within low to moderate heat stress risk thresholds, with no recorded episodes of extreme heat risk to date.
Regarding the time of day, the analysis shows that morning hours remain the safest part of the day, while high heat stress levels can persist until late in the afternoon.
The Union Cycliste Internationale (UCI), like Fifa and other international sports federations, has implemented safety protocols that assess heat risk and activate protective measures, such as hydration or cooling breaks in football. However, each federation defines its own risk thresholds, and no universal standard currently exists across sports.
Many heat safety protocols used by international sports federations are based on a heat index known as the Wet Bulb Globe Temperature (WBGT), which combines several meteorological variables – including air temperature, relative humidity, solar radiation and wind – to estimate heat-related health risk.
“Science still has many unanswered questions about how the human body responds to heat, and even more so in the case of elite athletes, who face sustained physical exertion while also having physical conditioning and training levels well above those of the general population,” said James Begg, researcher at Galson Sciences.
