Heat acclimation - just turn the fan off?

I’m off to Spain in a couple of weeks and it’s forecast to be about 31 degrees. Compared to around 16 here (UK) just now. I don’t deal well with the heat so hoping to acclimatise a bit before I go.

If I train indoors with the fan off, I get hot really quickly and my power drops, even if it’s pretty cold in the room.

Is this enough to acclimatise or do I need to actually get the heat in the room up?

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In the weeks before summer starts to really ramp up I’ll turn the fan and window ac off and do 20-30 minutes at low z2 near the end of my normal rides. Get a hard sweat going, but don’t boil. Drink lots while doing it… you can generate a comical amount of sweat.


It is probably enough, though to be extra sure you could put on a track suit. I don’t think you need to push the intensity, just z2 rides.

Get the fluids in, I like to weigh in before and after.

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Cheers both

Here is a paper on it: 5x 1h at 45% of threshold per week. Hydrate afterwards.


This is my favorite article on the topic:


these two in particular:

“Athletes can also perform heat acclimation training prior to traveling to a hot environment. An example of this occurred before the 1994 Track Cycling World Championships, which were held in Palermo, Italy. The US National Team trained on indoor trainers in a hyperbaric chamber at the Olympic Training Center in Colorado Springs, CO, which was set to replicate the high heat, high humidity, and low altitude (sea level) of Palermo. The strategy worked, and the team earned two golds, two silvers, and a bronze on the way to finishing third in the medal count.”

“Simpler methods of acclimatization training include wearing additional layers of clothing, sitting passively in hot sauna (heat exposure) or training in a hot room.”

A little more detailed info in this multi-part series

however it doesn’t offer any specific advice regarding indoor training environment, outside what I quoted above.

My personal experience is I’ve seen more benefits from increasing the temperature of the room to at least 26-28C, while still using a fan. That might not be so easy where you live. There are studies that have been mentioned on the TR podcast about using a sauna, instead of training in a warm room.

Hope that helps, and have fun in Spain!


Interesting to know thanks! In the paper I linked to they say that there isn’t a consensus about environmental conditions, but most studies are at at 30C. Though from that company who makes those core body temperature monitors they’re pushing any environment as long a core temp is at an appropriate level.

I’ve not read the articles you’ve linked to - but I assume they also talk about coming down slowly from the heat so to extend it. Mild dehydration can be effective too, but that needs proper adult supervision imho.

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Thanks. Yes, 26-28 might be difficult. I’ll see how hot I can get it though - be interesting to see which I find harder.

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I train outside, mostly in the heat of a California afternoon which is very similar to many parts of Spain. For me personally, the biggest impact is when I regularly train above 90F / 32C. Some of the biggest performance bumps I’ve seen were training blocks that included 1-3 days of 2 hours in 100F / 38C heat even though my power output was quite low (upper zone1 / Active Recovery).

This Scientific Triathlon episode:

discusses training in the heat. Dr Maunder said this (from the transcription):

"I did a study on heat training, which was HR controlled (i.e. both groups trained at the same HR % in hot and colder conditions respectively).

The group that trained in the heat rode at lower power due to the heat stress but by the end of the study, they performed better at a 30mins time trial after 2h of constant load work."

Starts at 34:36 of that podcast. The paper referenced is here: (PDF) Temperate performance and metabolic adaptations following endurance training performed under environmental heat stress which was a 3 week intervention training at either 18C or 33C.

In the words of my cycling friend and Kona age grouper “embrace the heat” (I’m a card carrying member of #TeamTina!)

Always fuel and hydrate. Mild dehydration? Terrible idea IMHO.

Agree. Except when done under proper adult supervision - it increases the blood plasma volume and that has good benefits for endurance athletes.

The paper I linked to was looking at hémoglobine increase through heat training. I know some teams and riders on smaller budgets are using it as an alternative to altitude camps. And it’s pretty accessible, ride for an hour after normal training in the heat at low intensity 5 times a week.

From the studies I’ve read I agree, the mild dehydration is actually the key that drives the plasma increase (probably best to err on the side of caution here though).

I’ve had a core body temp monitor for several months and acclimation can definitely be completed in “any” temperature, within reason.

Key differences are that if starting in a cooler temp the body takes a lot longer to heat up, so if going the route of doing it in a cooler room, the idea should be to do a harder workout and then extend the warm down without a fan to keep the body temp elevated. I’ve also had a lot of luck with buying a pvc sauna suit and elevating that way on an easier ride.

Studies seem to indicate acclimation can happen over a couple of weeks - I’m not sure if that’s the case or not because my own non scientific n=1 study was winging it 3 or 4 times a week for several months prior to summer. But I can say acclimation training absolutely works as I live on the beach in the SE USA which is obnoxiously hot and humid, and this summer has been an absolute breeze.

This was discussed in the last podcast. Training at lower watts but higher effort doesn’t lead to better performance, just to more riding at lower watts. That’s why we optimize training with carbs, fans, …

That said, specific adaptations to “race” conditions like heat adaptation can be helpful. But don’t give away your quality work for it. There are plenty of programs for adaptation eg riding Z2 with fan off. or better sauna post-exercise. A large effect is not due to hemoglobin but plasma volume increase.

In Spain your body will still benefit from moving air, just it’ll be warmer. By that logic I’d keep the fan (moving air) but warm the room.

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That’s prob enough but pretty hardcore. You could just purposely ride with extra clothes to have the same effect (and do it outside or inside). I like the fan on so I’d opt for the extra clothes route

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This sounds like the worst thing ever. Truly grim. Glad it worked for you though

It’s not great but it’s not horrible. Fact is, none of the protocols to actually drive true acclimation are pleasant. Even the passive sauna training is supposed to be completed immediately post workout when the body temperature is already elevated - I played around with that and it’s not exactly having a spa day.

Olympic champions protocols:

What I did was actually quite primitive: I just got on the turbo in my winter kit and did sessions in an overdressed state.”

In the five weeks before the Olympic road race, Kiesenhofer did three 90-minute overdressed sessions per week, monitoring her temperature using a Core sensor (a non-invasive device worn on the HRM strap), aiming for 38.7ºC.

“It’s a bit of a shame as a scientist, but my conditions were not really controlled,” she admitted; the basic aim was to get used to feeling very hot and sweaty. When Kiesenhofer got to Tokyo, she found that dealing with the heat was “a walk in the park” compared to her overdressed sessions on the turbo. In fact, she carried on wearing winter kit during her acclimatisation rides.

source: CW


  • In relation to heat acclimatisation, Flora did the test event in Tokyo in 2019, and we did a full heat acclimatisation protocol.
  • That ended up in a good way to understand her response and we understood she was ready.
  • The stress of the protocol was not high enough and therefore the focus was to building condition through more focus on training than focus too much on the heat acclimatisation.
  • Instead of doing a 10-day block of heat preparation, we stretch it to 4 weeks, and with a ramp of heat exposure during the block and taper them down.
  • In that way, the shock was not so high and so the training was not so affected.
  • The heat training involved a run or a bike session in a room in Flora’s house, increasing the temperature and humidity, without using a fan. For the swim sessions, we used wetsuits and a neoprene cap.
  • We did not use a passive strategy like a sauna or hot baths, because the athlete does not get familiar with racing in those conditions. Also, adding a sauna or hot baths adds more things and another stress to the athlete’s life and we believe that would not be beneficial to the athlete overall.

Source: ST podcast

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and since there is a lot of talk about the CORE sensor, finally an independent validation study. Well, so la la …

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Thanks for the study/abstract. And definitely agree there is still work to be done surrounding exact temperature as sometimes the monitor works flawlessly, and others it starts low, is slow to respond, and stays low.

I listened to that Nate Wilson podcast earlier and it was enlightening. What I’m really looking forward to is when the Norwegian triathletes actually go into detail on their process because it “seems” more scientifically backed rather than just putting on extra clothes, turning off the fan, and riding - or just training in a hot room. I’d like to see the science backing what they’ve done and exactly how they applied it.

There’s enough out there now to allow an amateur to kind of wing it and adapt, but hearing true protocols rather than just “get really hot and don’t drink for a while” would be beneficial.

From what I can tell, the top coaches are making this up as they go along right now. It seems like the goal for adaptations is to raise the core body temperature for some period of time.

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