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.
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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.
About Stephen Cheung
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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?
- 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.
- 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
- 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 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.
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