Athletes and coaches are always on the look out for ways to increase the Return on Investment (ROI) they get from the long hours they put in to training. They want an edge over competitors and improvement in the face of diminishing returns from their existing training methodologies. As a result, there’s been a lot of talk recently about heat training.

Heat acclimatisation - where you go and train in a genuinely hot environment - and heat acclimation - training in a simulated hot environment - have long been accepted as a proven way to improve subsequent performance in the heat. However it’s only relatively recently that people have started to look at heat training as a way to improve performance in temperate conditions too. That’s despite the fact that there’s research going back to 2010 that seems to demonstrate a clear link between heat stress training and improved exercise performance in cool conditions.

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How does heat training work?

Heat training is very likely to boost performance in temperate conditions because, as you train in the heat, your body adapts, increasing blood volume by expanding the plasma (watery bit) of the blood to make it flow more easily to the skin and working muscles. This helps with heat dissipation and provides a larger reservoir of fluid to lose in sweat before cardiovascular performance is compromised. This is something that’s also closely linked to hydration status and body sodium levels as it happens and that probably rings a bell if you’ve been a reader for a while or have chatted to one of our Sweat Experts in the flesh.

Heat training also re-sets your internal thermostat to run colder and you start sweating sooner. This means you have more room to play with, in terms of core body temperature rise, before that becomes a performance limiter, as can be the case in high intensity events where heat production from the working muscles can be extremely significant.

More people seem to adapt to heat training more quickly and reliably than they do to altitude training as well. Maybe that’s because we all evolved from common ancestors who came from the hot African savannah. This, along with the relative ease of implementation compared with altitude training makes heat stress training a very attractive option.

Image credit: Andy Blow ©.

Does heat training improve performance?

Having raced a lot in some very hot conditions over the years (Hawaii, Thailand, Saudi Arabia etc), I think I always tended to see a correlation between the amount of time spent in the hot environment pre-race and how well I performed. That relationship was pretty clear cut; simply preparing in the heat makes you more likely to do well in it, and it takes up to 14 days to get fully acclimatised to a hot environment (if you’ve been living somewhere cool for a while).

On the other hand, I’m not so sure I can point to any specific cases where I ever prepared or trained in the heat and then felt I had dramatically improved performances in more temperate conditions. I would almost always experience heavier training loads on training camps (which were usually in hot conditions), because that is exactly what I went along for, and therefore tended to see improved performances shortly after, but I couldn’t say whether that was a result of the heat or just the extra training. However, to be fair, I never really tried to link the 2 concepts together as it just wasn’t really considered something you would do a few years ago, so it’s hard to say for sure. 

In my capacity as Sports Scientist at the Porsche Human Performance Centre, I oversaw a hell of lot of heat acclimation training sessions in the heat chamber there. Our typical clients were racing drivers competing in the Middle East and Asia and runners competing in the Marathon Des Sables. We always tended to see some fairly dramatic and positive adaptions in terms of lower heart rates, lower core body temperatures and lower RPEs (ratings of perceived exertion - i.e. subjective notions of how hard exercise was) in athletes undertaking just 5 back to back heat chamber sessions over the period of about a week.

We saw that even a handful of 1 hour heat exposures (at about 35 degrees C and involving low to moderate levels of aerobic exercise) are enough to kickstart the body into becoming a lot more efficient at dissipating heat and conducting exercise in tough conditions. 

As we never tested performance in these athletes in cold conditions too, it’s only speculation that adaptations would have carried across into improvements there. But, based on the 2010 paper mentioned above and the increasing level of interest in heat training in general, it’s not a stretch to suppose this would have been the case.

And I know that when Jonny was prepping for The Canoe Marathon World Championships he travelled out two weeks early to acclimatise and he was also training in additional kit at home in the weeks beforehand (he even wore a bin bag in between layers a few times). He said that the first few days training in Singapore felt as though he hadn’t trained all year and he remembers that being particularly hard mentally, but a few weeks later he felt in great shape. Like me, he's not 100% sure whether it made the difference, but he thinks it was significant. 

I think that based on the evidence I’ve seen and the fact that researchers and elite athletes are increasingly interested in the use of heat training as a way to boost performance in cooler conditions, it’s something I would definitely consider experimenting with. If I was taking my racing and training at all seriously, I certainly would be building in some heat training into my plan. If you follow us on social media, you may have noticed that I’ve been running in some pretty hot places lately when travelling with work. I’ve definitely been putting my sweat rate to the test…

How to start heat training

Perhaps the best thing about heat training is that you don't really need specialist kit to do it. Your body doesn’t really care how it gets hot, so you can achieve at least some of the adaptations by just training in more layers of insulating clothing, rather than having to go into a special heat acclimation chamber.

Image Credit: Karen Stahlros via Unsplash (copyright free).

Regular saunas, hot yoga sessions and even just repeated exposure to hot baths have all been shown to exert at least some influence on heat-related adaptations in the body too, so it really is a type of ‘training’ accessible to just about anybody.

So, heat training might be something you want to try tinkering with even if your race calendar doesn’t include a trip to anywhere sunny in the near future.

Heat training safety advice

Of course, one important thing to note is that seriously overheating yourself can be very, very dangerous indeed. It’s critical that you’re sensible about it and make sure you’re not putting yourself at risk by training ‘hot’. Here’s some advice to bear in mind to stay safe…

  • Always let someone know what you’re doing and where you’ll be
  • Back off well before the signs and symptoms of heat illness begin.
  • Never put yourself in a situation where you could run out of drinks and always have a way to cool yourself down (i.e. the ability to remove clothing, or get out of the hot environment and into cool water/shade). And do so if you feel even the slightest need to. Heat stroke can creep up on you and is a killer if left untreated.

So, there you have it, the Precision Hydration verdict on heat training. If nothing else, heat training may be a good excuse to get away somewhere hot and sunny before your next big event…