Heat training for cyclists is one of the most underrated performance tools available. When the temperature climbs above 30°C, most riders see a 5-15% drop in sustainable power. Your body diverts blood to the skin for cooling, leaving less for the working muscles. Heart rate climbs. RPE increases. Everything gets harder.
But here's what most people miss: you can train your body to handle it.
Why Heat Destroys Performance
The physiology is straightforward. When your core temperature rises, your body faces a conflict — blood needs to go to working muscles AND to the skin for cooling. Something has to give.
At 35°C ambient temperature, cardiac output shifts significantly toward thermoregulation. Your heart rate climbs at the same wattage. Sweat rate increases. Glycogen burns faster. The longer the effort, the bigger the penalty.
This is why a rider who holds 280W comfortably at 18°C might struggle at 250W when it's 35°C and humid.
The Acclimatisation Protocol
Heat acclimatisation is a genuine physiological adaptation. Your body learns to start sweating earlier, produce more dilute sweat, expand plasma volume, and lower resting core temperature.
The 10-14 day protocol:
- Days 1-3: 60-minute sessions at Zone 2 in heat (indoor trainer with no fan, or outdoor if temperature is 30°C+). Reduce power targets by 10%.
- Days 4-7: Extend to 75-90 minutes. Start including some tempo work. Reduce power targets by 5%.
- Days 8-14: Full-length sessions with structured intervals. Power targets should be approaching normal by day 10.
Indoor vs Outdoor
A turbo trainer in a warm room with the fan off is actually the most controllable heat stimulus. You can layer clothing to increase thermal stress. It's miserable, but it works.
If you're preparing for a hot event like the Etape du Tour, start your heat block 2-3 weeks before.
Race Day in the Heat
Pre-cooling
Ice vests, cold towels on the neck, and slushy drinks before the start all lower core temperature and buy you time before you overheat. This is well-supported by research and used extensively in professional cycling.
Pacing
The biggest mistake is going out at your normal power. Drop your target by 5% and reassess after 30 minutes. You can always add power if you're feeling good. Starting too hard in the heat is a one-way ticket to the broom wagon.
Hydration and Sodium
In extreme heat, fluid losses can exceed 1.5 litres per hour. Read our hydration guide for the full protocol, but the short version: 700-900ml per hour with 500-700mg sodium. Pre-load sodium in the hours before.
Cooling Strategies During the Ride
- Pour water over your head and neck at every opportunity
- Ice in jersey pockets works surprisingly well
- Unzip your jersey on descents to maximise airflow
- Wet your base layer at feed stations
Common Mistakes
Not pre-cooling. Five minutes with an ice vest before the start is free speed.
Ignoring humidity. Dry heat is manageable because evaporative cooling works. High humidity with high temperature is where things get dangerous. Adjust expectations accordingly.
Skipping the acclimatisation. Flying to a hot event without heat preparation is leaving 5-10% of your performance on the table.
Key Takeaways
- Heat acclimatisation takes 10-14 days and produces real physiological adaptations
- Reduce power targets by 5-10% during the first week of heat exposure
- Indoor trainer with no fan is the most controllable heat stimulus
- Pre-cool before hot events with ice vests and cold drinks
- Increase hydration to 700-900ml per hour in extreme heat
- Drop race-day power targets by 5% and reassess after 30 minutes
- Humidity matters more than temperature alone — adjust expectations
- Heat training may even improve performance in cooler conditions
- Nail your race day nutrition alongside heat preparation
- Use the Fuelling Calculator to set carb targets — they need to increase in heat
