Heat adaptation and triathlon performance with Stephen Cheung | EP#138

In this interview we discuss racing in the heat and heat adaptation for triathlon and other endurance sports with professor Stephen Cheung, who runs a research lab investigating the effects of environmental stress on human physiology and performance.

• How heat affects triathlon and endurance performance.
• The best ways to mitigate the negative effects of heat.
• Heat adaptation benefits and protocols.
• Example: how to structure a heat adaptation training phase when preparing for Kona. 

3:45 -

• Stephen is a Professor at Brock University in Canada. 
• He runs the environmental ergonomics lab that focuses on the effects of environmental stress (e.g. heat) on human physiology and performance. 
• He's a competitive cyclist himself.
• He is the co-author of Cycling Science and Cutting Edge Cycling. 
• Stephen is also the chief scientist at Baron Biosystems. 
  • This is the company that has developed the innovative cycling software and app Xert.

5:30 -

• The first thing is, heat absolutely does impact performance.
• Even what we think of as comfortable room temperature (e.g. 20 degrees Celsius) already will impact performance. 
• If you want the best performance, you want to be competing and training in a relatively cool environment - around 10-15 degrees Celsius. 
• There have been studies looking at marathons around the world at different times of the year, across multiple years:
  • They have shown that the hotter it gets the worse the performance. 
  • This holds true for the very elite athletes, through to the less fit. 
  • The less fit individuals become more impaired as it heats up. 
• The impact for an average age grouper (mid-pack racer) may be around 10-15% in terms of performance, at around 20 degrees.
  • For the very elite, they may be impaired by around 5% because they are fitter and are finishing in a faster time anyway. 
• Cycling is different to running, as even at a moderate speed you are going faster than a typical runner. 
  • This means there's a lot more convected air flow which will help you cool off and evaporate sweat. 
  • With cycling you can get by competing in a much hotter environment as you won't be impacted as much.
• This is why you see in the Vuelta a España the cyclists can still handle it, even though it's very hot. 
  • Wind speed exponentially increases the cooling. 
• The caveat is that if you're climbing, you will be going a lot slower, and you can be impacted by the heat much more. 

9:26 -

• In 2004 my late colleague Gord Sleivert and I published a review about the different aspects of physiology that can be impacted by heat:
  • Multiple triggers for hyperthermic fatigue and exhaustion (2004)
• When you're hot, your brain simply cannot recruit muscles as well, or as intensely so there is a neuromuscular impairment.
• As you're sweating you are dehydrating more so there is a cardiovascular impairment.
• There is also an impairment because your skin blood flow increases a huge amount in the heat to try and get rid of the heat.
  • This diverts blood away from the muscles.
• It is also a perceptual thing, which is one of the newer areas being explored:
  • Heat impacts your cognitive functioning, your perception of effort, and therefore your motivation and willingness to exercise hard.

11:00 - 

• The best long term solution is to adapt to heat, and to do this slowly.
• My colleague Chris Tyler and I co-authored a big meta-analysis in 2016 looking at the effect of heat adaptation on performance of different kinds. 
  • We looked to see if there was a dose-response.
  • We also looked at whether there was a magnitude of response both in performance and the two classic adaptations of core temperature and your ability to have a lower heart rate. 
  • The main thing we found was that there is an improvement in performance over the course of adaptation. 
  • The amount of adaptation you can get is effective, even with a short term adaptation (3-5 days). 
  • However we did find that the longer you can do it (2+ weeks), the better you will be in all your physiological symptoms and actual performance.
• Evidence regarding a minimum level of temperature needed is vague because most studies use extreme heat. 
  • Very few studies actually look at passive heat adaptation - e.g. using a sauna or a hot bath. 
• We would say the main thing isn't the ambient temperature itself, it's getting your core body temperature elevated and sustaining it for a good period of time.
  • Ideally at least 1-1.5 hours a day. 
• You want to stimulate all of your physiological symptoms to adapt.
  • One of the big things is your sweat rate, so you can have increased evaporative cooling. 
  • We know that the longer you can get your body warm, the better you will stimulate those bodily systems to respond. 

14:30 - 

• You can exercise indoors, and maybe not have much of a fan on. 
  • This will allow you to generate a lot of heat and minimise the heat dissipation.
  • Your core temperature will heat up at a higher rate than if you were outdoors. 
• You can also go out and start exercising, and after around 1-1.5 hours once you're already warm, add extra clothes.
  • This is especially effective if you're doing intervals as you want to do them in the coolest environment you can to maximise the muscular and physical stimulus. 
  • After the intervals, if you are going to continue to do an endurance or a tempo effort (running or cycling), you can go and add the extra clothes.
  • This will keep the body temperature high over a sustained period, and it's a very effective way of doing it.
• There was a nice new study that came out this year from the University of Oregon:
  • They showed the simple act of putting on more clothing won't be as effective as exercising in 30-35 degree heat but it'll get you most of the way there. 
• The ideal is to be in an environmental chamber and set it to 35 degrees and exercise there for an hour a day. 
  • Obviously most people don't have access to that so these kind of 'heat adaptation hacks' will get you around 80% of the way there. 
• You may need a longer heat adaptation experience to get you closer.
• There was an interesting study recently from a research group in Denmark and Qatar:
  • They took Danish cyclists and had them do a time trial in Denmark when it was 5 degrees celsius and they averaged 300 watts. 
  • Then they went to Qatar where it was 30-36 degrees celsius and they trained for two weeks there. 
  • They tested them on arrival in Qatar, one week in and two weeks in using a 43km time trial. 
  • They found a 15% detriment in their TT time and power output when they first arrived, but at the end of two weeks they gained 98% back. 
  • This study shows there is an impairment but after 2 weeks you will mostly be adapted.
  • Interestingly they never got better than they were in Denmark, which highlights that you will still always be impaired in the heat. 
• To discuss the question of whether heat adaptation will improve general performance, that same group took the cyclists back to Denmark:
  • They found no effect when they did the time trial back in the cool environment. 
  • This shows that heat adaptation is really specific to the environment and it doesn't seem to be an ergogenic aid to competing in the cooler environments. 

20:07 - 

• You don't want the added stress of heat adaptation at the same time as your taper.
• If I was advising people getting ready for Kona, I would have the heat adaptation period well beforehand. 
  • Between 6-3 weeks out. 
• Once you're heat adapted you don't have to be training in the heat every day to keep that adaptation. 
  • Just 1-2 days of fairly mild heat exposure would maintain the heat adaptation well. 
  • Maintain the strategies you were using to acclimatise.
• I would advise doing your key quality workouts in a cool comfortable environment because you want to maximise that physical training.
• Heat adaptation process should be focused on the other parts of training. 
  • E.g. If after an interval session you're going to be riding easy, take that time to put on extra clothing. 
• If you have an endurance day, spend this doing heat acclimation. 
  • E.g. Riding indoors with less cooling to maximise heat.  
• Don't combine the intensity work with heat adaptation.
• If you have the luxury of a heat acclimation period of 4 weeks you don't necessarily need to exercise in the heat every single day. 
  • You could get by with every other day, or 3-4 times a week. 
  • During that induction period I would definitely avoid doing it on hard, intense days. 

24:23 - 

• The first thing is to wear light, and lightly coloured clothing on race day - don't go with all black kit. 
  • The simple absorption of heat by dark clothing will be a factor. 
• For cycling, the main thing is to stay hydrated because you want to be in the best condition for the run. 
  • You have a fair amount of cooling when cycling at high speeds so it's not as much of a concern. 
• For the run, wearing a light and lightly coloured singlet, and a cap, can be helpful. 
  • The other benefit of a cap means you can pour water over it at aid stations, which keeps cold water near your head. 
  • This will help with the evaporation. 
• Most triathlons are so long that the concept of 'pre-cooling' which rowers or TT cyclists may employ don't come into play.
  • You're swimming in a relatively cool water temperatures anyway. 
• If you're at aid stations, pour water over your head and torso to maximise heat dissipation.
• I would intuitively agree that a cap is more protective than a visor.
  • One of the big advantages is pouring water and holding it close to your head, which you can't do with a visor. 
  • Go with a lightweight, tech fabric cap. 

20:03 - 

• The classic symptoms of heat adaptation is that your core temperature at rest and during exercise is lower. 
  • You are not near a dangerous or critical threshold where you may be in trouble.
• Your heart rate will also generally be lower.
  • This is because yo have increased plasma volume so your heart has more blood to circulate to your skin and muscles. 
  • It isn't as stressed, and so your heart rate is lower. 
• With time, your sweat rate increases and your sweat electrolytes tend to become lower and more dilute.
  • Your body has learnt to conserve and re-absorb electrolytes. 
• Cognitively and perceptually you become more comfortable working hard in a hot environment.
  • This psychological change should not be discounted. 
• Don't underestimate the impact of heat, and plan for it in advance. 
  • Whether it's extra hydration, stocking up more at feed stations and training yourself to experience discomfort in the heat.  
• Be aware of exertional heat illness.
  • If your brain starts getting foggy, that's one of the key symptoms of impending heat collapse. 
• If you find your gait is staggering, that's another classic symptom.
  • Your central nervous system is shutting down, and it can't help you move properly. 
  • This is hard to diagnose in yourself, but it's a call to action for race doctors and aid station workers. 

31:21 - 

• The most interesting talk was pulling back on the focus on performance we have all the time. 
  • It was by Curtis Cramblett who is a physio and bike fitter from San Francisco. 
  • He gave a nice keynote on rehab and performance, and the different steps in looking at rehab from injury. 
  • He had a diagram of a pyramid, at the base was health, in the middle was fitness and the top was performance. 
  • His point is that many of us chase the top of the pyramid while neglecting the basic health.
    • E.g. proper hygiene, sleep, nutrition, mechanics, form etc. 
  • Focusing on this first as your foundation, from then you can build fitness and only then you can focus on performance.

• Cycling Science and Myth Busting Part 1 with Stephen Cheung | EP#74
• Cycling Science and Myth Busting Part 2 with Stephen Cheung | EP#75
• Advanced power training with Xert - Armando Mastracci and Stephen Cheung | EP#86
• Brain training and psychobiology of endurance performance with professor Samuele Marcora | EP#17
• Scientific Triathlon training camp in the Algarve, Portugal, 20-27 Ocotber 2018
• Xert Cycling Software
• ​PEZ Cycling News Toolbox
• How to measure your sweat rate to improve your hydration strategy
• How to estimate how much sodium you lose in your sweat

Connect with Stephen Cheung 

• Through his Brock University email
• On Twitter: @EELBrock

Connect with host Mikael Eriksson

Hi! I'm your host Mikael,

I am a full-time triathlon coach and an ambitious age-group triathlete. My goal is podium at the Finnish national championships within the next few years.

I first started the website Scientific Triathlon in autumn 2015 as a passion project to share my learnings with a larger triathlon audience. Later on, in early 2017 I started the podcast That Triathlon Show. 

I sincerely want you to contact me to

• Send me feedback
• Give constructive critic​ism 
• Request topics and guests for the podcast
• Send me your triathlon-related questions 
• Tell me that you've rated and reviewed That Triathlon Show so I can give you a shout-out on the show and tell you how much it means to me!