Podcast, Racing, Science

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

 July 16, 2018

By  Mikael Eriksson

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.

Discuss this episode!

  • Let's discuss this episode and the topic in general. Post any comments or questions in the comments at the bottom of the shownotes. Join the discussion here!

In this Episode you'll learn about:

  • 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. 

Sponsored by:

Precision Hydration

Precision Hydration
One size doesn't fit all when it comes to hydration. Take PH's free Triathlon Sweat Test to get personalised hydration advice tailored to what you're training for. Use the promo code THATTRIATHLONSHOW to get your first box or tube of electrolyte product for free!

The finest triathlon wetsuits, apparel, equipment, and eyewear on the planet. Trusted by Lucy Charles, Javier Gómez-Noya, Flora Duffy, Mario Mola, and others. Visit roka.com/tts for 20% off your order.


About Stephen Cheung 

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.

Impact of heat on exercise performance

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. 

Physiological changes that make us slow in the heat 

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:
  • 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.

Mitigating the impact of heat 

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. 

Strategies for heat acclimation

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. 

Example: heat acclimation for Kona

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. 

Other heat adaptation strategies

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. 

Physiological effects of heat adaptation

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. 

What did you learn from the Cycling and Science conference? 

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.

Key takeaways

  • 20 degree Celsius (68 degrees Farenheit) can lead to a 10-15% performance detriment compared to 10 degrees celsius.
    • If you want to race in a hot race, the key is to be heat adapted, and incorporate this into your training. 
    • Other acute strategies can be used during the race itself, but heat adaptation is the most important thing.  
  • Heat adaptation doesn't work like altitude training - you can't just do heat adaptation protocols and expect to have a benefit in moderate temperatures. 
    • Heat adaptation minimises your losses when racing in a hot environment. 
  • There has been a fair amount written about pre-cooling in endurance sports in recent years, but this is not really relevant for triathlon.
    • Triathlon has it's own pre-cooling with the swim! 

Links, resources and contact

Links and resources mentioned

    Connect with Stephen Cheung 

    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!
    Subscribe to That Triathlon Show and never miss an episode!


    Let's discuss this episode and the topic in general. Post any comments or questions in the comments below. I'll be here to reply and take an active part in the conversation, so don't be shy! 

    Mikael Eriksson

    I am a full-time triathlon coach, founder of Scientific Triathlon, and host of the top-rated podcast That Triathlon Show. I am from Finland but live in Lisbon, Portugal.

    Please contact me if you have feedback on the podcast or want to make suggestions for improvement or send in a question for a Q&A episode.

    If you are a long-time listener and appreciate the value the podcast brings, please consider taking a couple of minutes for leaving a rating and review on iTunes/Apple Podcasts, or wherever else you can think of leaving a rating and review.

  • Really enjoyed it. This is the “space” we’re focused on. Constant, sustainable cooling on the bike. 15-25 degree reductions in skin temp while you’re riding for as long as you ride.

  • {"email":"Email address invalid","url":"Website address invalid","required":"Required field missing"}

    Explore our products and services