Heat Adaptation Training

Heat and humidity. Anyone who exercises in the heat knows it can have a significant negative impact on performance. Do you know you can train your body to perform better in the heat? Similar to training your muscles and cardiovascular system with exercise, or training your gut to process more calories for race day, we can also use heat adaptation protocols to improve our body’s response to hot conditions. This can put you at a significant advantage to your competition (or just make your exercise more productive and enjoyable), if your body is more heat adapted.

With the heat at the Olympics last year, there was a lot of discussion on the potential benefits of heat adaptation training (https://www.cbc.ca/amp/1.6090826? ). A particularly interesting article I came across recently was from Alex Hutchison, who does a great job of reviewing / interpreting studies. In this article (https://www.outsideonline.com/.../how-to-heat-proof-your.../) he discusses how a recent study demonstrated that doing heat-specific adaptation training, provided additional benefits beyond just training in the heat. The key point here is that simply training in hot weather may not provide as much benefit as specifically working on heat adaptation via a defined protocol (or in conjunction). He also covers that heat adaptation provides some benefits for as long as a month afterwards. So… you don’t have to do it all the time, but it may be good to do periodically, particularly in advance of key races where heat may be a factor (e.g. those of you doing Gravel Worlds coming up).

Do you know that while exercising, your core temperature rises? Besides ambient temperature, most of the energy we utilize it converted to heat, rather than power to propel our bodies or bikes. For example, 75% of the watts produced on a bike (or more) are converted to heat, so if you are riding at 200w, you are generating 600w of internal heat that needs to be dissipated… into potentially high ambient temperatures. This is what we are trying to better address with heat adaptation training… making the body more effective at managing core temperature. The body’s primary mechanism for dealing with increasing core temps is dissipating that heat with evaporation from sweat. This change in phase (liquid to a gas) absorbs a lot of heat, allowing heat losses even with high ambient temps (e.g. even when riding in the desert with outdoor temps in the 120’s, we still are able to lose heat through evaporation of sweat). The adaptations we get are increased blood volume, increased sweat rate, and earlier onset of sweating. How high can core temps be when exercising? Using Core temperature sensors, I regularly see athletes at 101-102 degrees F, even up to 103 degrees at times. Shockingly, in this paper (https://bjsm.bmj.com/content/53/7/426 ), athletes were observed hitting temps up to 105 deg F during time trials… yikes! For reference, the general recommendation is that at 103.5 F, there is a risk of heat exhaustion and at 104 F or more, it’s the classic definition of heat stroke (from a medical perspective). The key point is we want to manage core temp through better adaptations, to limit performance degradation and health risks.

Heat adaptation protocols themselves have been around and utilized for many years in various formats. They can be useful in driving adaptations that may help your body perform better in warm environments. Again, the overall goal is to maintain cooler core temperatures by sweating sooner after the onset of exercise, increasing sweat rates overall, and decreasing the amount of electrolytes lost in the process (more info located here). Part of the adaptation is increasing blood plasma volume, which may also have some additional performance benefits for some athletes*.

In the past, many of the studies and protocols were driven around the use of Saunas. This study from 2015 demonstrated a significant increase in plasma volume (17.8%) after four uses. This study from 2007 found an increase in athlete performance in time trials, after extended (21 days) sauna use. More recent focus has been on the use of hot baths for driving adaptations, as more athletes have access to a bathtub at home, and it may be easier to maintain specific temperatures than can be achieved in a shared sauna at a health club. Two studies were done, showing similar results, both demonstrating reduced skin temperature, reduced time for sweating onset, and improved performance in the heat. The first study in 2015 was with recreational athletes, and the follow-up study in 2018 was with endurance-trained athletes. A study in 2019 showed that the heat adaptation benefits can last two weeks, and another study from 2019 showed that even if you delayed the protocol until well after the exercise session (8 hours), you could still get heat adaptation benefits (although not quite as large).

One of the authors of the two hot bath studies first cited above, did an interview with MySportScience with practical guidelines on using a hot bath protocol, which can be found here. I highly recommend you review this link before doing any heat adaptation protocols, as heat adaptation protocols can add additional stress to the body and can be very taxing. The key infographic for this article is:

Again, if you are interested in utilizing this strategy to prepare for the heat, please review the documents/links carefully. Make sure you consult with your medical professional to ensure that your body can handle heat adaptation training. Note that heat adaptation training increases the stress the body sees, so you may need to cut your training back accordingly. It is critically important that you approach this in a safe and methodical manner. From both personal experience and feedback from many of my athletes, it’s a good idea to drink fluids while in the hot tub (or sauna) to help maintain hydration. I’ve personally lost 2-3 lbs in 30 minutes in a warm tub… keep your fluids up, just as you would when you exercise. As noted in the article, don’t try to go warmer than recommended. An inexpensive digital meat thermometer may be helpful in verifying the temps. It can also help to stir the water in the tub periodically, to help ensure that you maintain good heat transfer during the session (this helps keep the temp more uniform overall). Lastly, and most importantly… Listen to your body… if anything doesn’t feel right or feels bad, stop the heat adaptation protocol immediately.

* There have been some studies that have shown increasing plasma volume can increase performance, beyond just racing/training in warm weather. This study shows heat adaptation training improved exercise performance in both warm and cooler conditions. This study from 2019 and this study from 2020 both showed that hemoglobin mass increased after plasma volume increased (weeks after the increase), potentially increasing oxygen delivery after heat adaptation training over time.

Want more detailed information on heat adaptation? Check out the following podcasts of interest:

a) https://podcasts.apple.com/.../heat.../id1529312639... . This first one is from Anne Guzeman interviewing Stephen Cheung, who is recognized as one of the best researchers in environmental conditions (exercise, work, etc.). He gets into the discussion of different types of methods (e.g. riding when it's hot/or on the trainer vs sauna/hot bath), as well as providing just a great overview of the basics. This is a great place to start learning about heat adaptation. One interesting comment Stephen made was that females "may" need just a little longer for adaptation than males (a couple/few days more).

b) https://podcasts.apple.com/.../the.../id1545953110... . This second podcast is from Huberman lab. This gets into more of the brain interface with heat, as well as detailed discussions on sauna protocols and studies specifically. There are also interesting discussions on heat/cold protocols, and how they may be used to reduce cortisol and increase human growth hormone. Some different discussions than traditionally discussed when it comes to heat/heat adaptation.

Train smart!

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