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Published on March 12, 2026 at 06:00 AM
As one of the few people lucky enough to do Ironman Coeur d’Alene in both years where the temperature reached 105 degrees F (yes, that takes a special kind of luck — I’m not allowed back on CdA), I can tell you that performance absolutely suffers, undoubtedly in the heat. And not just at extreme temperatures – Bike power can decrease by up to 15% at temperatures above 85 degrees Fahrenheitand Running strides can slow down by up to 30 seconds per mile For every 10 degrees above 60°F.
With these effects in mind, athletes have long relied on heat training to acclimate and reduce its effects on training and racing. Heat training allows your body to tolerate heat — especially exercising in the heat — by stimulating adaptations that help you maintain a lower core temperature and improve your thermal tolerance.
While the standard two-week heat training protocol has been used for years to achieve heat acclimation, Recent research Extended heat training protocol provides thermal acclimatization, he explains and Improve overall performance. Which means heat training might just be your new secret weapon.
Heat training induces a variety of physiological adaptations to develop both heat tolerance and performance gains. It’s a simple process, so bear with me here. We’ll go through it step by step.
When you are in a hot environment, and especially when you exercise in a hot environment, your core temperature rises. Your body knows this isn’t ideal, so it works to counteract that. The way our bodies lower core temperature is by cooling the blood circulating through the core – the internal organs, muscles and deeper tissues. This is done through evaporative cooling.
Evaporative cooling occurs when the sweat on our skin evaporates. In fact, evaporating sweat absorbs heat from the skin and blood in the capillaries near the surface of the skin, thus cooling the skin and blood. This cooled blood then returns to our bodies, reducing our core temperature (or at least preventing it from rising much higher).
So when our body senses a high core temperature and wants to boost evaporative cooling in response, it:
With regular, prolonged exposure to heat, our bodies get better at managing the effects of heat. It lowers the temperature at which sweating begins and increases Sweat rateto start the evaporative cooling process early and make the most of it. It also increases the volume of blood plasma (the liquid component of our blood), so our heart does not have to beat as quickly to fill dilated superficial capillaries, and more cold blood can be circulated and returned to the heart. This is heat acclimation, and can be achieved after two weeks of heat training.
But here’s where things get interesting: Modern studies It showed that if you continue heat training for another three weeks, you can also See performance gains across all environments.
So we stopped increasing the volume of blood plasma in our body to provide more blood volume for more cooling. When this happens, our blood components become poorly balanced: too much plasma, and relatively fewer red blood cells (RBCs). A low number of red blood cells means low hemoglobin, the protein in red blood cells that carries oxygen from the lungs to the muscles. Our kidneys detect this low hemoglobin and think we are in a state of hypoxia, or low oxygen. It doesn’t sound great, but it actually works for us.
In response to perceived hypoxia, our kidneys release the hormone erythropoietin, or EPO (yes, that EPO). EPO’s job is to stimulate the production of red blood cells. More RBCs mean more hemoglobin, which means more oxygen can be transported from the lungs to our muscles. This makes your kidneys happy, but it also increases your activity Voiceover2TopThe maximum amount of oxygen your body can utilize during exercise. (Caught your attention there, right?)
We can also look at the benefit of increased oxygen transport through the lens of aerobic metabolism. The aerobic – or oxygen-dependent – energy system provides the primary fuel source for our muscles when exercising. So increased oxygen delivery capacity of our cardiovascular system translates into increased fuel production capacity in our muscles. Which means you can now produce the same output – the same force or pace – at a lower heart rate. Or, by flipping this idea, you can produce greater output—higher energy and faster strides—with the same heart rate. This is exactly what improved performance looks like.

Now that you are 100% sold on Benefits of heat training – For your next hot and humid race or any other race on your calendar – let’s talk about what heat training looks like in practice. Because although the gains are great, achieving them requires commitment and diligence.
Research studies that have shown performance gains have used a five-week heat training protocol. The first two weeks of the five weeks are sufficient to develop heat acclimation. Weeks three, four and five are when performance gains appear. If you only have two weeks and your primary goal is to acclimatize to the heat, this will get the job done. Do you have three or four weeks and hope to improve performance? You will likely still see some gains.
But it will require frequent – almost daily – heat training. The studies involved five thermal training sessions per week, either active (while active) or passive (while sedentary). Four to five sessions per week will likely be sufficient during weeks three to five, but aim for five sessions per week for the first two weeks of heat training.
While studies have used active or passive heat training, in practice, we can mix the two, combining active and passive heat training sessions to meet our weekly requirements. Whether your heat training session is active or passive, the goal is to increase your core temperature over an extended period to stimulate physiological responses associated with heat acclimatization and improved performance.
In conjunction with increasing your core temperature, you also want to limit your body’s ability to use evaporative cooling. This helps keep your core temperature higher for longer, further promoting adaptation and improving thermal tolerance (your comfort in hotter temperatures).
Specifically, heat training sessions look like this:
According to studies, heat training sessions should be between 45 to 60 minutes long. Passive heat training is best done immediately after a cardiovascular training session, as you will start the heat training session with an already elevated core temperature. If your cardio session that doubles as an active heat training session exceeds 60 minutes, use the last 45-60 minutes for heat training so that – similar to passive heat training – you start the heat training portion with your core temperature already elevated.
Jumping straight into a 45-minute heat training session where you’re fully submerged in a 104-degree Fahrenheit hot tub may feel like jumping straight into high-intensity intervals or four-hour bike rides after several months on the couch. We can use the same approach to progression of heat training sessions that we use for cardiovascular training: start with what you can handle—such as 20-30 minutes at 100-103 degrees Fahrenheit—and then gradually increase the duration and/or temperature each session until you reach your goals.
When scheduling heat training sessions during an already full training week, it is important to understand that heat training stresses the body just as cardiovascular training does. Passive heat training should always come with it after Cardiovascular training sessions, ideally not within 12 to 18 hours of a high-intensity cardio session.
You’d never want to incorporate active heat training into a high-intensity cardio session; Even endurance sessions will likely see lower output when combined with active heat training. You may also need to reduce the overall intensity of your swim, bike, and running training weeks during heat training, due to the additional stress on your body from the heat training protocol.
(By the way, the stress on your body from heat training also means that more is not better. Going beyond five weekly heat training sessions or 60 minutes during a single session creates more stress and fatigue than it adds benefit.)
Because of the additional stress on the body when heat training is put to the high demands of a full swim, bike, and run training week, it’s best not to overlap your heat training protocol with peak training weeks, when your training stress is greatest, or tapering off before a race, when you want to prioritize rest and recovery.
But the benefits of heat training don’t last forever — these hard-earned adaptations largely disappear after two weeks without heat training. However, you can adopt a maintenance schedule of two or three heat training sessions per week to maintain heat acclimation and improve long-term performance.
Best final takeaway? If you’ve always wished you could incorporate altitude training into your season but logistics and expense have made it impossible, heat training is an excellent alternative: it offers similar performance gains, greater flexibility with timing relative to race day, and you can save a lot of travel expenses.