Heat training is one of the most underused performance levers available to amateur cyclists. Not because it's complicated or expensive — most riders just don't know it works, or they assume it's only relevant when racing in July. It's not. Done correctly, heat exposure boosts plasma volume, stimulates haemoglobin production, and delivers performance gains that transfer to cooler conditions too. Think of it as altitude training, but without the mountain.
Why heat makes you a better cyclist
The core adaptation starts in your blood. When you exercise in a hot environment, your body loses fluid through sweat faster than it can replace it. To compensate, blood plasma volume expands — sometimes by as much as 20% within the first few days of heat exposure, before settling around a 10% sustained increase. That's a significant shift in your cardiovascular system. More plasma means the heart can pump more blood per beat, cardiac output rises, and — critically — the blood becomes somewhat diluted, causing a drop in haematocrit. That drop triggers your kidneys to release erythropoietin (EPO), the same hormone that altitude camps and, illegally, blood doping aim to elevate. The EPO signal pushes your bone marrow to produce more red blood cells, and over several weeks, total haemoglobin mass goes up.
The knock-on effect is real. A 2010 study in the Journal of Applied Physiology found that 12 trained cyclists improved their VO2max by around 8% and their functional threshold power by 5% following just ten days of heat acclimatization — gains that rival what you'd expect from a three-week altitude camp. A 2022 study by Rønnestad and colleagues showed that five weeks of regular heat sessions (five per week, around 50 minutes each) produced a near-3% increase in haemoglobin mass. For experienced cyclists who've already picked the low-hanging fruit of structured training, those numbers are remarkable.
There's also a thermoregulatory side to all of this. Your body learns to sweat earlier and more efficiently, which keeps core temperature lower during hard efforts. Resting heart rate drops slightly. You become less sensitive to heat stress, which matters a lot during summer sportives or multi-day events where heat accumulation over several hours quietly degrades power output without you fully noticing it happening.
How long you actually need to do it
This is where most cyclists get misled by oversimplified advice. Short blocks — a week or ten days — do produce noticeable thermoregulatory adaptations. You'll sweat sooner, feel more comfortable in the heat, and probably pace yourself better in warm conditions. But for the haematological benefits that transfer to cooler riding — the higher haemoglobin mass, the improved VO2max — the evidence is pretty clear that you need at least five weeks of consistent exposure. Studies using 10–14 day protocols found no meaningful increase in haemoglobin mass or cool-condition performance, even when plasma volume rose significantly. The plasma expansion is the trigger, but erythropoiesis takes time. Short-term heat training gives you a fraction of the benefit. Longer blocks give you the full package.
For most time-crunched riders, the realistic target is three to five sessions per week of 45–60 minutes in a hot environment. This doesn't need to be a chamber or an expensive sauna. Training with extra layers or a thermal vest works — a 2021 study in the International Journal of Sports Physiology and Performance found that overdressing and using an environmental chamber produced comparable haematological results. If you have a turbo trainer in a warm room, that's genuinely sufficient. Some athletes finish rides with a 20–40 minute hot bath, which adds passive heat exposure without extra training load — a reasonable option during periods of high fatigue.
Fitting heat training into your season
The most obvious use case is preparing for a hot race or sportive. Two weeks of specific heat acclimatization before a target event in warm conditions will meaningfully reduce the performance penalty of racing in heat. Let's be honest: most riders arrive at a summer event having done zero preparation for the heat, then wonder why they feel terrible at kilometre 80. Even a week of regular sauna sessions after rides will help.
But the bigger opportunity is using heat training as a substitute for altitude camps — or as a complement to them. If you're building your base over winter and spring, adding a 5-week heat block in February or March can elevate your haemoglobin mass before your A-events in summer. Some elite teams now integrate heat sessions as a standard part of their training calendar, not just as a pre-race preparation tool. The adaptations are real, they're legal, and they don't require travelling anywhere. If you're interested in seeing how LeCoach can help you plan and track a structured heat training block alongside your regular cycling sessions, it's worth exploring.
One practical note: don't try to do hard interval sessions in the heat. The physiological stress of combining high-intensity work with heat is substantial, and the risk of overreaching is significant. Use easy to moderate intensity rides (think zone 2, occasionally zone 3) for your heat sessions, and keep your hard intervals in cooler conditions. The heat exposure itself is the stimulus — you don't need to be suffering through VO2max intervals at 38°C to get the adaptation. Also, maintain around two or three sessions per week minimum to avoid letting the adaptations decay; the thermoregulatory gains fade faster than the haematological ones.
What to watch out for
Heat training isn't without risk, and the main concern is straightforward: dehydration and heat illness. Begin sessions with full hydration, monitor your resting heart rate in the mornings (a useful signal of accumulated heat stress), and don't train through warning signs like persistent headaches, unusual fatigue, or disorientation. If you're stacking heat sessions on top of a high training load, something has to give — either the volume, the intensity, or the heat. Trying to do all three at once is a recipe for a forced rest week.
For riders doing hot baths as passive exposure, 38–40°C for 30–40 minutes post-ride is the protocol used in most research. Going hotter or longer doesn't proportionally increase the benefit, and the risk of feeling genuinely unwell goes up. Drink electrolytes during and after, and give yourself time to cool down before sleeping.
If you're already using a periodised training plan — whether through a coach or a platform like a structured weekly programme — heat training integrates cleanly alongside it. It's not a replacement for good periodisation; it's an addition that amplifies the work you're already doing.
Sources
- Lundby C et al. (2023). Hematological, skeletal muscle fiber, and exercise performance adaptations to heat training in elite female and male cyclists. Journal of Applied Physiology. Link
- Rønnestad BR et al. (2021). Five weeks of heat training increases haemoglobin mass in elite cyclists. Experimental Physiology. Link
- Cubel M et al. (2024). Time-course for onset and decay of physiological adaptations in endurance trained athletes undertaking prolonged heat acclimation training. Temperature. Link