Heat Acclimation for Runners: A Coach’s Analysis

Trail runners and ultramarathoners are groups that like to take on challenges. The tougher, the better, right? In a quest for new and tougher challenges we go longer, higher, hillier, and sometimes hotter. If we choose to face the heat, it may be appropriate to apply various degrees of heat acclimation. The type and degree of heat acclimation call for depends on the race. When heat quietly plays a factor, such as at the Western States 100 or the Vermont 100, running during the heat of the day or driving around with the heat on might be enough to take the edge off on race day. However, when the heat is more likely than not to be a headline feature of the event, such as at Badwater… or the Marathon des Sables, more strenuous heat acclimation. In this post you’ll find some background on heat acclimation, additional heat acclimation resources, and my personal experiences with heat acclimation for MdS.

Background Information on Heat Acclimation for Athletes

Considering the only heat acclimation I’d ever done before this week was driving from Park City to Moab, Utah and back with the heater on in June (for the record, it was quit toasty in the car), I went to an expert for advice. Greg Loomis was the man I called on, as he has advanced medical training, was involved in researching heat acclimation for the Army, and ran for a year in the Sinai while serving in the Army. Here’s what Greg had to say:

Human’s ability to sweat allows us to cool our bodies even when running in extremely hot environments. However, the need to circulate blood out to the skin periphery for this cooling draws this much needed blood away from working skeletal muscles and causes a lower cardiac filling and stroke volume leading to higher heart rates at any given work load. The loss of electrolytes and fluid via the sweating (without adequate replacement) will lead to a decreased blood volume and add additional demand on an already taxed heart.

Heat acclimatization is one way to improve ones ability to run well in a hot environment and in extreme cases is necessary for survival. Heat acclimation is merely when an individual has been conditioned to maintain a higher blood plasma and volume level, increased sweat rate, a decreased salt amount in the sweat produced, decreased fatigue rate of sweat glands, and quicker onset of sweating when placed in the heat. These changes are all needed to meet the demands on the body mentioned above. Heat acclimation is produced via repeated exposure to heat sufficient to raise body core temperature. This is most effectively done by exercise (skeletal muscle contractions) vs. sitting in a hot room. Only a few sessions of one hour of moderate exercise in the heat will produce an effect in un-acclimated individuals with changes being seen in a few days.

Some interesting highlights to acclimatization:

  • One can become acclimatized to heat and cold at the same time. Even with training bouts being on the same day in the different environments.
  • Most of the improvements in heart rate, core and skin temp, and sweat rate are acquired in just ONE week of heat exposure. Heart rate adaptations are seen in just 4-5 days! However increases in sweating and a feeling of “ease of walking” in a hot environment can take up to one month to occur.
  • More is gained from a 100 minute bout of heat exposure exercise than one 50 minute bout, but adding bouts beyond 100 minutes of exposure did not quicken adaptation.
  • Heat exposure adaptations have been studied to disappear as quickly as one week if the subject is not re-placed in the heat, but may last as long as 3 weeks in some individuals.

All facts taken from “Human performance physiology and environmental medicine at terrestrial extremes” Pandolf, Sawka, Gonzalez. ISBN: 1-884125-02-6

Additional Heat Acclimation Resources

While Greg provides some great background on heat acclimation, you may want to jump even deeper into the physiology and process of heat acclimation – I know I did. Fortunately, the military has published Medical Aspects of Harsh Environments, Volume 1. Section 1 of this publicly-available tome contains over 300 pages of the physiology of and adaptation to heat. Of particular utility is Chapter 2 – Human Adaptation to Hot Environments (pdf) in which I found the discussions of thermoregulatory control, thermoregulatory responses during exercise, and factors that alter heat tolerance to be wonderfully useful. These discussions taught me how the human body reacts to heat and how these reactions will change with heat acclimation. Heavy with references – Human Adaptation to Hot Environments will put you in the know on everything from how non-acclimated whites have a very high concentration of sodium in their sweat to the variation in adaptions to dry and humid heats.

After you’ve conquered the Army’s heat acclimation resource or if you are looking for something that more directly addresses various processes for heat acclimation, check out the International SportMed Journal’s Heat Adaptation: Guidelines for the Optimisation of Human Performance. This article discusses the advantages and disadvantages of heat adaptation in athletes before diving into various methods of heat acclimation, including:

  • Natural acclimatisation
  • Passive heat acclimation
  • Exercise-induced heat adaptation
  • Combined exercise-heat acclimation with exploration of
    • Constant work-rate regimens;
    • Self-regulated exercise regimens; and
    • Controlled hyperthermia regimens

While less “scientific” than the previously noted resources, Arthur Webb’s article Heat Training in the Sauna found on the Badwater website worth reviewing. While less of a research piece, this article offers insight into the actual process someone uses to heat acclimate for Badwater. There’s even a day-by-day sauna time and temperature schedule… which reassured me that folks can survive the type of sauna sessions I wanted to attempt.

My Heat Acclimation Experience

Enough about about smart people with penchants for authoring well-referenced academic medical publications and more about me. Most people would follow the conventional wisdom about heat acclimation and do something along the lines of hitting the sauna for two or three 10 minute periods during their first heat acclimation sessions, but not me. Instead, I saw Greg’s mention of 50 minute sessions and jumped right in.

On Monday, I went to Gold’s Gym on a free trial membership. After waiting around I was pleasantly surprised to learn they had a dry sauna rather than a steam room. “Perfect,” I thought to myself. Not long thereafter, I found myself sitting in a 160 F room. No, that’s not a typo there, it was one-hundred and sixty oven-like degrees in the room. I felt like a roasting turkey. All I lacked was a thermometer sticking out of me. It took a couple minutes for the sweat to start rolling off me and it wasn’t long after that when I began feeling slightly nauseous. By about 10 minutes, I was setting into a groove. I just sat there or stood up and did some light stretching. By 20 minutes, I was quite uncomfortable and not at all enjoying myself. I did some more stretching and was amazed at how much greater my flexibility was than normal – I felt like rubber man. When not stretching during this time, I was trying to read a fellow MdS runner’s analysis of the race’s nutritional needs and was having a really hard time comprehending it. My lack of comprehension was not because the material was overly difficult or poorly written (the analysis has been incredibly approachable and useful at normal temperatures); rather, my mental faculties were clearly deteriorating. By 25 minutes, I was kinda scared and really pressing to stay in the sauna. Around 27 or 28 minutes, I was freaked out and settled on bailing at 30 minutes. Those last two minute seemed to take forever. Upon leaving the sauna, I went straight for a cool shower to lower my core temperature.

Less than 10 minutes later, I was back in the sauna to finish up my 50 minutes. These 20 minutes went by much like the first except I was slightly more in control of my emotions. I can’t say the same for my cognitive ability. Reading and understanding took my full concentration and even then I felt like I was missing things. I was very happy for the session to be over, but felt very, very weak afterwards. Within 15 minutes, I was at Chiptole. Sure, I was picking up dinner, but what I really wanted was a huge iced beverage with some quick calories to restore my strength.

I decided to be all gung-ho and jumped back in the sauna again on Tuesday, this time with the intention of remaining for the full 50 minutes. I didn’t try to read at all during this session and listened to music instead. Even without the need for deep thought, I once again caught my mind faltering. This was really eye opening in that before I head to Morocco I need to have my nutrition and hydration decisions made and have them down pat. I also have to be on the lookout for heat-induced mental retardation and only slowly and deliberately make decisions once I notice this effect.

Another thing I need to be on the lookout for is panic. I was seriously on the verge of panicking a couple times during this second session. The panic ultimately lead to me leaving the sauna after 45 of the 50 minutes that I had intended to be in the sauna. This was a good lesson to learn before hand. Knowing that this could be a real problem on the course, I’ve already set out to find ways to combat the panic.

Aside from becoming aware of the slowed cognition and panic that heat can induce, this second session was damn stupid. I felt horrible went I was done. I stood in the cold shower for 7 or 8 minutes immediately afterward, all the while feeling very weak and nauseous. On Wednesday morning I was completely without energy on my run to work. I continued to feel “off” throughout the day and into the evening. Stupid, stupid Bryon.

One fun thing that did come out of Tuesday’s sauna session was a heart rate profile that clearly shows the effect of heat exposure on heart rate over time. The first 45 minutes show my time in the sauna with a steadily increasing heart rate despite the fact that I rarely moved much. From 45 to 52 minutes, I was standing in a cold shower attempting to lower my core temperature as quickly as possible during which time my heart rate plummeted. From 52 to 60 minutes, I was getting to and leaving Gold’s. After that, I was running home. Enjoy … I sure didn’t! ;-)

The effect of heat (160 F dry heat) on heart rate over time.


  • Have you ever tried to heat acclimate for a race?
    • If so, what did you try?
    • Do you felt like it worked?
    • Have any interesting stories?
  • Do you know of any other useful heat acclimation resources?

There are 15 comments

  1. Gavin Boyles

    Bryon, have you tried overdressing? Just go for your regular runs (at regular HR) but wear a ton of clothing, hats, etc. I have no physiological basis for this, but it seems like that would be more race-specific than sitting in a 160-degree sauna. And be careful in there!

  2. Bryon Powell

    Gavin,I haven't tried the overdressing route. Not sure that I'd be able to get myself out the door wearing many layers and rain gear. The clothing route would be more specific in that I'd be exercising in the heat. On the other hand, I think that in order to get hot enough I'd be creating a humid microclimate around my body, which would not create the same adaptations as the very dry air of the sauna.As for the sauna, I will definitely be careful in there. Now that I have a baseline reading for my HR, I'll use that as a warning system. It appears as though my thermoregulatory system maxs out at slightly more than 140 bpm – I'll get there, hold it for a little while, and leave.

  3. Ultrarunning-Edge

    Bryon:In terms of Gavin's suggestion, wrestlers have been doing this sort of thing for ages as a means of weight loss. When I wrestled in high school, we used to have the heat cranked up to 80 or 85 F in the gym, and we wore plastic sweat suits while doing 30-45 minutes of calisthenics. Many of us ran for an hour or two several times a week in the suits, as well. (Badwater participants have also been known to train this way.)I've never had to deal with anything like the heat of MdS, although I've done a number of races during excessively hot (for the USA) temperatures. In my experience, by far the most effective preparation is a form of speedwork called heat stress training. Basically you do three or four 25-30 minute periods of tempo running (at or just below anaerobic threshold) spaced out by 10-15 minutes at recovery pace. (You do these workouts at 'normal' temperatures.) This is effective for two reasons. First it simulates the prolonged high heart rate produced by heat (which you experienced). Second it trains the brain to believe that it is possible to continue exercising under these conditions.

  4. Anonymous

    Hi Byron, sorry you found my nutritional analysis so confusing to read (although, it might not be you, it was a pretty rough draft!).Overdressing and exercising will give you some benefit, even though it would create a more humid microclimate. The key to induction of the physiological changes is raising your core temperature by about 1.5C for a period of time. Exercise can do this, as that is why well trinined athletes (i.e. VO2max > 60) already have many of the adaptations needed. As a previous poster mentioned, interval/tempo training can help Aas well, again by raising core temp. However, it will be very difficult to get prolonged periods of increased core temp through this method…It probably isn't neccesary to sit in 160F temps – 100-11-F with some activity is probably all you really need. It is hard to find this type of enviornment though.Train well,Bill

  5. Bryon Powell

    Bill,Sorry if I didn't make it clear, but it wasn't your writing that was confusing. Rather, the confusion was purely a function of my brain no longer working at top speed. I've read you nutritional analysis at regular temperatures and it's quite understandable and much appreciated as is! :-)I agree that it would be ideal for me to find a lower temperature room (100-130F) and exercise in it. Unfortunately, the dry sauna that I have access to is set to 160 F and the setting is not amenable to exercise (i.e., it's a tiny room in which nobody moves or makes noise).

  6. Bob - BlogMYruns.com

    feeling very weak and nauseous.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Hey Bryon I am a sauna freak the past month…I started out at 20 minutes but now around 35-40 mins, my sauna at 24 hour fitness is 185 degrees. and yes ONCE a week I go in until I get to the point of pukeness–lol last week 56 mins(really wanted 60 mins but thought I was going to explode) it's my mental game to tax myself and then afterwards sit on the bench for a few minutes to recover…ahhhh good times :-) and lastly it does drain the you a lot!!PS: You didn't mention water I don't think but when I go in the sauna I always bring in at least 3 bottles of water…finish at least 2 always and one for afterwards.I do notice I FREEZE indoors at sales meeting etc… Good Post & be careful bro in da sauna :-)

  7. Dan Moore

    I've never done any specific heat acclimation, but I have lived and run through the summer in Las Vegas, NV and St. George, UT. I've often been asked how I can run in July and August in the heat.What surprises people is that May and June are always the hardest months for me, by July I've built up to it and usually feel fine.I don't know that this helps much if you're going someplace that will be suddenly and shockingly hotter than where you live, but I would suggest building up gradually to avoid hurting yourself, just like you build mileage.

  8. Meredith

    I did heat acclimation in the sauna prior to crewing and pacing at Badwater last year. First off, 50 minutes your first time in, is A LOT, imo. I eased into it. By the last few weeks I was in the sauna for 45-60 minutes about 3 times a week. Drinking water in there is VERY important. Also, towards the end, I would wear my Badwater clothes (long sleeve and long pants) in there as well, prior i was just in a sports bra and shorts. The panic and claustrophobia happened to me, especially towards the end of each session. I also am an antsy person, so even without the heat it would be difficult for me. I own an infrared sauna that goes to 140F, the infrared mimics the sun's heat, so even though it does not get as hot as your gym's sauna, i feel it still did the job. Proper hydration throughout the day is also very important when you are doing sauna training, as well as being mindful of your electrolytes. I always got in the sauna after my run or workout and thought that worked best, cause i was already hot to begin with.

  9. Bryon Powell

    UE,Good point about learning to exercise when you're mind doesn't think it can continue doing so. I'm hoping that putting myself to the brink of panic repeatedly will at least give me the skills to cope with those doubts. I'd try the multiple tempo session method, but at this point it doesn't fit into my training. All of my hard days are packs runs… and it's almost taper time. One of the things about heat acclimation is the ability to do so in a short period of time… should mesh nicely with a taper on the running front.Bob,What the heck are you doing in a sauna these days? I'm pretty sure it's not gonna be pushing 100 at Umstead.Can't say that I've done much drinking during my sessions. I didn't drink at all during my first session and only drank 16 ounces total during my most recent two sessions (45 and 50 minutes at 160F).Dan,Sound advice about building up slowly, but at this point I'm already at my maximum intended duration. I'm hoping it gets easier from here.I hear ya on the easier in the heat of summer thing. Some of my worst heat experience in the mid-Atlantic have been during the sudden onset of hot and humid conditions in April or May.Meredith,Good point about doing the sauna after your exercise. First, the exercise does bring the body temperature up going into the sauna. Second, it'd be a beast to do any sort of real workout after initial or intense sauna sessions!

  10. Meredith

    It does get easier. You should have eased into it, silly! LOL. At first it was hard for me to even do 30 minutes, but after several weeks, i could do 45-60 minutes. I just had to remind myself that i could not open the door and escape death vally, nor can you escape the desert at Mds! LOL. I would stop the heat training right prior to the race to make sure you are well hydrated, you will not lose the heat endurance you built. Especially since the long flights and travel will only further dehydrate you. The only thing i never did in the sauna was wear shoes, even though i wore my long sleeve and long pants in there towards the end.

  11. Bryon Powell

    Meredith,I will probably heat train right up until I leave, as I have a couple days between leaving the states and racing. Good point about the travel hydration.I wore shoes the first day in the sauna as I didn't bring flip flops. I was very happy they were END's WOW water shoes as I would have been walking around in fish bowls otherwise.

  12. Sophie Speidel

    Goat,John Dodds pointed me to the heat acclimating article on the Badwater website, which I followed with much success when preparing for WS in 2006. I started at the end of May, a few times a week, no more than 10-15 minutes at a time and built up to 50 minutes by the Saturday before the race…then I backed off and hydrated all week. I also brought in a water bottle and did yoga and light core strengtheners (planks and crunches).Check out the article—it's on that website somewhere.

  13. Bryon Powell

    Sophie,There area number of interesting heat-related articles, including heat acclimation articles, on the Badwater website. I'd printed and read one before publishing this post. As you've pointed it out, I'll take it as a sign that the article is noteworthy enough to include in the post itself. Thanks.

  14. Robert

    Ebay has felt hats for the sauna. They are to keep your brain from frying. No affiliation, but think about it – away from the sauna.

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