As the Tour de France approaches, every detail in a
contender’s preparation is scrutinised. So when a fan, Josep Termens, spotted
Jonas Vingegaard training in 30-degree heat, fully kitted out in long sleeves
and tights, it sparked curiosity. “It was 30 degrees, and he was wearing long
sleeves and tights,” Termens noted.
To the casual observer, it might have seemed odd, even
uncomfortable. But for those following the evolving science of endurance
training, Vingegaard’s choice fits a growing trend among elite cyclists: heat
adaptation training.
The idea is simple but the physiology is very complex.
Training in hot conditions, especially while deliberately over dressed, forces
the body to respond to thermal stress. This leads to a cascade of adaptations
that are highly valuable not just for racing in heat, but also for enhancing
overall endurance performance, even in cooler weather.
So, let’s find out why Vingegaard is dressed for winter in
June!
The science behind heat training
When an athlete trains in heat, their core body temperature
rises more quickly and remains elevated for longer. To cope, the body initiates
several changes:
Plasma volume expansion: One of the first
and most important responses is an increase in plasma volume, the liquid part
of blood. More plasma means more blood volume, which improves cardiovascular
stability, enhances oxygen delivery, and aids thermoregulation. This is
particularly useful during long climbs or sustained efforts. E.g. Col de la
Loze!
Vingegaard has two weeks to optimise his Tour shape
Improved sweat response: Training in heat
also increases the sweat rate and improves the body’s ability to begin sweating
earlier. This helps regulate core temperature more efficiently during
competition.
Reduced HR: As the body adapts, athletes
often see a reduction in heart rate at a given power output or pace, due to
more efficient cooling and improved cardiac function. It’s the same reason
altitude training is valued too.
Increased Mitochondrial Efficiency: Some
studies suggest that heat stress may enhance mitochondrial function, increasing
the muscles’ ability to produce energy aerobically. In a Grand Tour, that can
translate into better sustained efforts deep into stages or over consecutive
days.
More than just heat acclimatisation
It would be easy to assume that Vingegaard is simply
preparing for hot conditions in France. After all, recent editions of the Tour
have included searing stages in southern France, the Pyrenees, and the Alps,
often surpassing 35 degrees Celsius. But what makes heat training particularly
attractive is that the benefits extend well beyond acclimatisation.
Even if race day temperatures are moderate, the circulatory
and muscular improvements from heat stress persist. Unlike altitude training,
which requires long adaptation blocks and can negatively impact high intensity
power in the short term, heat training delivers measurable gains in aerobic
efficiency without major trade-offs.
And who, in previous edition has (allegedly) struggled in
the heat?
Yes, last year he won at a canter, but that wasn’t the case
in 2023. In particular on the Col de la Loze, a mix of altitude, heat, and
fatigue saw Vingegaard spectacularly crack Tadej Pogacar.
Moreover, heat adaptation can be achieved relatively quickly,
some athletes notice changes within five to ten sessions of training in heat or
using over dressing strategies. For someone like Vingegaard, who is still
building form, the technique offers a low risk way to maximise physiological
return in a compressed timeline, with now just two weeks until the Tour begins.
Risks and drawbacks
Of course, this isn’t without drawbacks. Training in high
temperatures or while over dressed places a significant strain on the body,
increasing the risk of dehydration, electrolyte imbalance, and even heat
illness if not carefully monitored. It also reduces the absolute intensity an
athlete can sustain during the session, meaning heat blocks are often used for
endurance rides rather than intervals.
All in all, it is incredibly uncomfortable.
But Vingegaard, riding with the support of Team Visma |
Lease a Bike’s performance staff, is unlikely to be mismanaging the process. If
anything, the choice to wear tights and long sleeves in the midday sun is a
clear signal that his preparation is back on track and focused on physiological
efficiency rather than optics.
A fan Josep Termens who caught Jonas Vingegaard in training before Tour de France said this: "It was 30 degrees, and he was wearing long sleeves and tights.”
— Lukáš Ronald Lukács (@lucasaganronald) June 21, 2025
But do you why he is doing it? It’s a heat training. And why it is that good?
Heat adaptation training is so effective… pic.twitter.com/txocwcz9pc
Fin MajorCycling Journalist
Fin Major is a UK-based writer at CyclingUpToDate and has been part of the team since 2024. He is the site’s main writer for FAQs and evergreen explainers and has written around 2,000 pieces for the platform. Alongside this work, he focuses on in-depth analysis and covers the biggest races on the calendar, including the Tour de France, the Giro d’Italia, and La Vuelta a España, providing clear context around performance trends, tactics, and key storylines.
In his reporting, Fin uses reputable data sources such as ProCyclingStats for results, statistics, and historical context. He places strong emphasis on careful sourcing, editorial accuracy, and updating articles promptly when new, verified information becomes available. Outside of writing, Fin is an active cyclist, which supports his practical understanding of the sport and its demands.
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