Heat training for the yellow jersey of the Tour de France

Heat training is a must for this Tour de France . Not just because the sun shines in France and an athlete's body needs to be well adapted to the heat. No, heat training provides an extra boost of performance even in more moderate temperatures. The most successful cycling teams are firmly convinced of this.

"Actually, heat training was the only thing we did differently in preparation for this year's Tour than in the past four years," says Kristof de Kegel, sports scientist and employee of the Belgian racing team Alpecin Deceuninck. The Dutchman Mathieu van der Poel, who has worn the leader's yellow jersey for several days in this Tour, and Jasper Philipsen are also riding there. The Belgian took the stage win and the yellow jersey on the first day of the Tour de France, but dropped out on the third day after a serious crash .

Do the racers feel the improvement from heat training? "Yes, the whole team is strong, that's why we believe it," de Kegel told DW. "There's no 100 percent proof. But when we look at the performance of the whole team now and what we're doing differently compared to previous years, then I would say: Yes, that's true."

Targeted fever for better performance

The coaches of defending champion and top favorite Tadej Pogacar of Slovenia also swear by the extra boost provided by heat stimuli. "We supplement the altitude training with heat training," sports scientist Jeroen Swart of Pogacar's team, UAE Emirates XRG, told DW. The goal is to raise core body temperature to 38.5 degrees Celsius, thus creating a slight fever.

Heat training can be done passively, Austrian professional cyclist Felix Gall explains to DW: "Then you go to the sauna after training or take a warm bath. With active heat training, you put on extremely heavy clothing on the last climb in the altitude training camp or then go on the roller [a device that allows you to train on a bike without moving from the spot - editor's note]."

Is heat training more effective than altitude training?

Carsten Lundby has been researching the effects of heat and altitude training, as well as the combination of both, for about ten years. "In my opinion, heat training is more effective than the type of altitude training that most cycling teams do today," says the sports scientist from the Danish University of Odense.

This is primarily because more people respond to the stimuli that heat triggers in the human organism than to the stress caused by thin air at altitude. "The effects of heat training are much stronger and also much more widespread than those of altitude training," says Lundby. "Some people don't respond at all to altitude training. However, it's very rare for someone to not respond to heat training. Heat is a much greater stressor than altitude. If I had the choice between the two forms of training, I would always choose heat training."

His studies have shown, among other things, that heat training not only increases blood volume. The increased fluid volume can ensure that red blood cells are better distributed in muscle tissue, allowing more oxygen to reach them and improving performance. The stress factor of heat also stimulates the formation of new red blood cells, thus doing exactly what one would hope for from altitude training.

Deliberately subjecting the body to this stressful situation poses certain health risks, particularly to the cardiovascular system and mental health. For professional racers, who are constantly monitored and supervised by doctors, health problems such as dehydration, mineral loss, respiratory problems, heatstroke, sunstroke, and sudden drops in performance are usually easily controlled and preventable.

Formula 1 and marathon runners also use heat training

The training method isn't entirely new, at least not for German champion Georg Zimmermann, who is also competing in the Tour: "I've been a big fan of saunas for years. It's almost a hobby of mine. So I was doing it before the topic even came up, without knowing it was training."

Rolf Aldag, former professional and sports director of the German team Red Bull-Bora-hansgrohe, even knows some very early adopters: "At the 1992 World Championships in Benidorm, Miguel Indurain [five-time Tour de France winner from Spain - editor's note] arrived wearing a thermal jacket and leg warmers. That was 33 years ago."

Back then, that was considered unusual. Today, sports scientists at professional cycling teams are integrating heat training into their routines. Heat training is also en vogue in other sports. The Formula 1 racing teams Ferrari and Red Bull had their drivers undergo special heat training before the 2022 Singapore Grand Prix. Heat training is also becoming increasingly popular among marathon runners.

Chance for smaller teams to catch up

In cycling, heat training can have an additional positive effect: Putting on thick clothing or taking a hot bath is far less expensive, time-consuming, and strenuous than an altitude training camp. Teams with smaller budgets could catch up with the industry leaders here.