Heat training for cycling works if you give it 6 to 14 days. The 2015 consensus on training and competing in the heat, written by Racinais and 16 colleagues, puts near-complete heart and sweat adaptation at 6 to 10 days of an hour or more a day, and about two weeks for endurance performance in the heat.
How long does heat acclimation take?
Most of it comes in the first week. The consensus authors recommend sessions of at least 60 minutes a day that raise both core and skin temperature enough to make you sweat, and they report that trained riders can adapt in up to half the time of untrained people. Heart rate at a given effort comes down, sweating starts earlier and plasma volume rises.
Tyler, Cheung and colleagues pooled 96 studies in Sports Medicine in 2016. Heat adaptation moderately improved exercise capacity and performance in the heat, programmes shorter than 14 days already produced many of the benefits, and the largest changes came from programmes longer than 14 days. So 10 days is a sensible minimum for a rider with a fixed date, and two weeks is better.
What the cycling trials found
| Study | Riders | Heat programme | Result |
|---|---|---|---|
| Lorenzo and colleagues, 2010 | 12 trained cyclists, 8 controls | 10 days at about 50% of VO2max in 40°C | Time trial work up 8% in 38°C and 6% in 13°C, plasma volume up 6.5% |
| Keiser and colleagues, 2015 | 7 men, crossover | 10 days of 90 minutes in 38°C | 30 minute time trial up 10.4% in 38°C, no change in 18°C |
| Cubel and colleagues, 2024 | 20 elite male cyclists, 10 in heat | 6 one-hour sessions a week for 5 weeks | 15 minutes longer to exhaustion in 40°C, sweat rate up 0.44 L an hour, gone 2 weeks after |
| Richard and colleagues, 2025 | 15 trained women, 11 in heat | 10 home turbo sessions overdressed in 2 weeks, then 9 in 3 weeks | Faster 20 km time trial in 35°C, no change in controls |
Lorenzo, Minson and colleagues gave the clearest number for what heat costs. Before acclimation, their 12 trained cyclists did 718.7 kJ of work in a time trial in 38°C against 879.8 kJ in 13°C, about 18% less. Ten days of heat training lifted the hot figure to 776.2 kJ.
Does heat training improve performance in cool weather?
The evidence splits. Lorenzo's group found a 6% gain in cool conditions too, 879.8 kJ to 934.7 kJ, and a 5% rise in VO2max, with no change in their 8 riders who trained in the cool. Keiser, Lundby and colleagues tested the idea in a crossover, so each of their 7 men did 10 days of training in 38°C and 10 days in 18°C. Heat training raised plasma volume by 6% and time trial performance in 38°C by 10.4%, and performance at 18°C didn't change.
Our view at WattPlan is that heat training is worth the effort before a hot event and not as a general winter performance tool. The cool-weather gain rests on one trial against a crossover that found none, while the gain in the heat shows up in every study in the table.
How do you heat train at home on a turbo?
Turn the fan off and dress up. Richard, Cheung and colleagues had trained women ride a stationary bike at home while overdressed, 10 sessions over 2 weeks. Their peak power and 20 km time trial in 35°C improved, and their 4 controls, riding at the same heart rate in normal conditions, didn't change. With 11 riders in heat and 4 controls, treat it as a lead.
The consensus sets the dose. An hour or more, hot enough to sweat steadily, on most days for 6 to 14 days. In practice that means your easy and endurance rides in the plan, done in a warm room with extra layers and no fan, at the heart rate you would normally ride them. Keep hard intervals out of the heat at first, because heat raises heart rate at any given power and a session that is hard in the cool can become much harder in the heat. Drink to replace what you lose, since the hydration guide shows how far sweat rates already vary before you add heat.
Heat sessions add strain, and the consensus authors write for healthy riders. If you have a heart condition or any other medical condition, talk to your doctor before you start.
How long does heat acclimation last?
Two to four weeks for most of it, according to the consensus, which also reports that re-acclimating is faster than the first time. Cubel's elite cyclists lost theirs sooner. After 5 weeks of heat training, their exercise capacity in the heat and their physiological adaptations were back to where they started 2 weeks later. So time the block to finish in the last few days before you travel, or keep it topped up. Richard's group kept improving with 9 maintenance sessions over 3 weeks, about three a week.
What WattPlan reads during a heat block
A ride with power is scored against your FTP, so an endurance ride at the same watts gets the same Load in a hot room as a cool one, while your heart rate will sit higher until you adapt. Rate how hard each session felt, at the end of a session in the player or on the ride's page afterwards, and if two planned sessions in a row feel two points or more harder than planned, WattPlan's Coach is told to ask about sleep, fuelling, heat or illness and to ease the next hard day. Set a location on your target event and WattPlan's briefings in the final days before it include the forecast temperature when one is available, with the three-day briefing's clothing advice built on it. The race week guide covers the days after your heat block ends.
What to do before a hot sportive
- Count back from the day you travel. Start the heat block 12 to 16 days before it, so that 10 to 14 sessions finish in the last few days at home.
- Do 60 to 90 minutes a day of easy or endurance riding on the turbo in a warm room, overdressed, with no fan.
- Hold your usual heart rate, not your usual power, and expect the watts to drop in the first sessions and climb back as you adapt.
- Keep your hardest intervals cool for the first week, then move one a week into the heat if you want the practice.
- If the event is more than two weeks after the block ends, ride two or three warm sessions a week to keep what you gained.
What we don't know yet
Every trial in the table is small, none was blinded, because you can't hide a hot room, and Lorenzo and Richard had 8 and 4 controls. Only one trial was all women, the protocols differ in temperature, humidity and session length, and the best home method for a working rider, overdressing, a hot bath after riding or a sauna, hasn't been compared head to head in any cyclist trial we found. How fast acclimation fades also varies between riders, which is why the consensus figure of 2 to 4 weeks and Cubel's 2 weeks don't agree.
Sources
- Consensus recommendations on training and competing in the heat, British Journal of Sports Medicine
- The Effects of Heat Adaptation on Physiology, Perception and Exercise Performance in the Heat: A Meta-Analysis, Sports Medicine
- Heat acclimation improves exercise performance, Journal of Applied Physiology
- Heat training increases exercise capacity in hot but not in temperate conditions: a mechanistic counter-balanced cross-over study, American Journal of Physiology Heart and Circulatory Physiology
- Time-course for onset and decay of physiological adaptations in endurance trained athletes undertaking prolonged heat acclimation training, Temperature
- Three weeks of heat maintenance potentiates the benefits of heat acclimation in trained females, Physiological Reports