Heat training has become one of the most talked about performance tools in endurance sport. From WorldTour cyclists training indoors in winter jackets to professional triathletes spending time in saunas and hot baths, more athletes are using heat as a deliberate training stimulus. But despite the growing evidence, many age-group athletes still avoid it altogether.
The question is simple: does heat training make you faster, or are you simply making yourself suffer for no reason?
The reality sits somewhere in the middle.
Why Heat Training Works
When we expose ourselves to heat, the body begins to adapt. Over time these adaptations can include:
- Increased plasma volume
- Lower heart rate at a given intensity
- Earlier and more efficient sweating
- Improved cooling capacity
- Better tolerance to hot race conditions
- Reduced cardiovascular strain
- Improved endurance performance
Interestingly, many of these benefits are not limited to racing in hot conditions. Athletes often report lower heart rates, improved aerobic efficiency and better perceived effort even in cooler environments.
Heat exposure effectively becomes another training stress, much like altitude, strength training or high-intensity intervals. Used appropriately, it can enhance performance. Used poorly, it can simply leave you exhausted.
Why More Athletes Don't Do It
If heat training is so effective, why doesn't everyone use it?
The answer is simple: it is uncomfortable.
The goal of most heat sessions is to elevate core temperature for an extended period. That means feeling hot, sweating heavily and often experiencing significantly higher heart rates than you would expect for the power or pace you are producing.
Many athletes mistake these sessions for easy recovery rides because the power output is low. In reality, the physiological stress can be substantial.
Heat is an additional training load.
If you simply add heat sessions on top of an already demanding programme, fatigue can accumulate quickly and performance can suffer.
The Hidden Risks
1. Excessive Fatigue
One of the biggest mistakes athletes make is underestimating the stress of heat exposure.
A Zone 1 ride without fans may feel easy from a muscular perspective, but the cardiovascular load can be considerable. Many athletes report feeling drained for the remainder of the day following their first few sessions.
When introducing heat work, something else often needs to come out of the programme.
2. Dehydration
As your body adapts, sweat rate increases. This is actually one of the desired adaptations, but it also means fluid losses can become substantial. Many athletes lose between 1.5 and 2 litres of fluid per hour during heat sessions.
Allowing body mass to fall significantly through dehydration provides no additional benefit and simply increases stress.
A useful guideline is to avoid losing more than 2% of body weight during a session and to replace approximately 150% of the fluid lost during recovery.
3. Poor Sleep
If body temperature remains elevated into the evening, sleep quality can suffer. For athletes already balancing training, work and family life, poor sleep can quickly undermine recovery. This is one reason why many athletes complete heat sessions earlier in the day.
4. Doing Too Much Too Soon
More is not better. The body adapts surprisingly quickly to heat. Research suggests meaningful adaptations begin within five sessions, with the majority occurring within 10 to 14 exposures.
You do not need months of suffering to gain benefits.
What About Fertility?
This topic occasionally appears whenever heat training is discussed. Current evidence suggests any effects on sperm quality from heat exposure appear to be temporary and reversible. There is currently little evidence linking sensible heat training practices to long-term fertility issues.
For athletes actively trying to conceive, discussing concerns with a healthcare professional is always sensible, but the current evidence does not suggest recreational heat training presents a significant long-term risk.
How We Use Heat Training at Optimal Endurance
Heat training is not something we prescribe to every athlete. Instead, we tend to use it in three situations:
1. Preparing for a hot race
Events such as Kona, Nice or Lanzarote, can all present significant thermal stress. Arriving prepared for the environmental demands can be just as important as your fitness.
2. Building durability
For experienced athletes with good training consistency, carefully introducing heat sessions can provide another endurance stimulus without increasing mechanical load.
3. Improving heat tolerance
Many athletes simply struggle in warm conditions. Improving sweat response and cooling efficiency can dramatically improve confidence on race day.
Practical Ways to Heat Train
Indoor Sessions
- Easy endurance ride
- Reduced fan use
- Additional clothing layers
- 45 to 60 minutes of sustained heat exposure
Post Exercise Hot Bath
- Immediately after training
- 40°C bath for 30 to 40 minutes
- Lower overall training stress than riding in the heat
Sauna Exposure
- Following easy sessions
- Short exposures initially
- Gradual progression
The objective is not to produce your highest power numbers. The objective is simply to elevate body temperature and allow the body to adapt.
Our Recommendations
For most age-group athletes:
- 2 to 3 sessions per week initially
- 7 to 14 days to gain meaningful adaptation
- Reduce overall training load slightly
- Increase carbohydrate intake
- Prioritise hydration and electrolytes
- Monitor recovery carefully
Heat training should make you fitter, not simply more tired.
Final Thoughts
Heat training is not magic. It will not replace consistent training, good nutrition or sensible recovery.
But when used appropriately, it is one of the few interventions that appears to benefit almost every athlete. Unlike altitude, where responses can vary considerably, heat adaptation seems remarkably consistent.
The key is respecting the stress. Train hard enough to create adaptation, recover well enough to absorb it, and use heat as another tool rather than another opportunity to suffer. Because ultimately, the goal is not to survive the heat.
It's to perform when everyone else starts to slow down.
Coach Jack