Health & Sports Science

How Elite Athletes Train to Compete in Extreme Heat — The Norwegian Method

On July 12, 2026, the Tour de France shortened a stage for the first time in 123 years as temperatures neared 40°C. While most riders struggled, the Norwegian-Danish team Uno-X Mobility thrived — thanks to a data-driven heat acclimation system that is changing how endurance athletes prepare for a warming world.

• Ten days of carefully controlled heat exposure can expand an athlete's plasma volume by 6.5%, increasing cardiac output and oxygen delivery to working muscles. This translates to a 6% improvement in time-trial performance in cool conditions and 8% in the heat.
• Norwegian coach Olav Aleksander Bu uses CORE body temperature sensors combined with frequent finger-prick lactate readings to calibrate each athlete's heat training — building tolerance by training without air conditioning and avoiding cold drinks during sessions.
• The method has produced results at the 2026 Tour de France: Tobias Hallend Johannessen finished second in heat-shortened stage nine, and Torstein Træen wore the yellow jersey for two stages, proving athletes from cold climates can outperform rivals in extreme heat with the right preparation.

The 2026 Tour de France is being run during Europe's most intense heatwave on record. On July 12, with road temperatures exceeding 50°C in direct sun and riders stuffing ice bags down their jerseys, organisers cut 30 kilometres from stage nine between Malemort and Ussel. It was the first time in more than a century that the Tour shortened a stage for weather reasons.

Amid these brutal conditions, the Norwegian-Danish team Uno-X Mobility emerged as one of the race's surprise performers. This was no accident. Coach Olav Aleksander Bu, a pioneer of the data-intensive Norwegian endurance training method, has spent years perfecting a heat acclimation protocol that he now applies to every rider on the team.

The core principle is simple: repeated, supervised exposure to heat triggers physiological adaptations that make the body more efficient at cooling itself and delivering oxygen. The standard protocol involves 90-minute training sessions in warm conditions over 10 to 14 consecutive days. Athletes are instructed not to use air conditioning or consume cold drinks during workouts, because the body must learn to cope with rising core temperature rather than bypassing the adaptation process.

What makes Bu's approach distinct is the precision of measurement. Each rider wears a CORE sensor, a small patch that continuously monitors internal body temperature via the skin. Bu also takes frequent finger-prick blood samples to measure lactate levels during training. By correlating core temperature with lactate curves, he can identify precisely when an athlete's cooling system is under stress and adjust the training load accordingly.

Research published in sports physiology journals has quantified the benefits. A 2026 study found that ten days of heat acclimation expanded plasma volume by 6.5%, meaning the heart has more blood to pump with each beat. This raises cardiac output and enhances the delivery of oxygen to muscles — a benefit that persists even when athletes return to cooler conditions. In controlled time trials, heat-acclimated cyclists improved their performance by 6% in cool conditions and 8% in the heat, compared with non-acclimated controls.

The implications extend far beyond professional cycling. As global average temperatures rise and extreme heat events become more frequent, athletes across all endurance sports — from marathon running to football — will need to adopt heat training strategies. The Norwegian method, with its emphasis on precise physiological monitoring, offers a blueprint for competing safely and effectively in the hotter conditions that define modern sport.