How to perform better in the heat

I won't go into it in too much detail as Andy covered it in his blog on 220 Triathlon on how hot weather impact your body when you train and race, but heat can have a detrimental impact on your performance. Thankfully, there are proven – and a few less-proven – strategies to cope with it that'll benefit swimmers, runners, cyclists and triathletes alike...

I recently attended the fourth Science & Cycling Conference in Nantes, France and one of the speakers, Stephen Cheung, addressed how to maximise performance in the heat.

Cheung is a Professor at Brock University and heads up the Environmental Ergonomics Lab. Cheung wrote the popular academic tome Cycling Science and has advised numerous professional cyclists and World Tour teams, plus the military, on how to perform in hot conditions.

‘Fatigue and discomfort in the heat isn’t just down to one factor,’ Cheung explains, in a deep, confident tone at odds with his slight, almost delicate frame. ‘Core temperature plays a key role, especially it's impact on a variety of systems.

As a snapshot, this rise in temperature alters brain chemistry and impairs cognitive function; it changes gut bloodflow, causing leakage into the system; it increases free radical damage… we’re talking a multi-faceted system. It’s not simply a case of core temperature rises and you perceptibly feel uncomfortable.’

This discomfort can develop into a clinical problem like heatstroke and its knock-on effect mentally. I remember a good friend of mine suffered such severe heatstroke at the Weymouth Middle Distance Triathlon years ago that he ended up in hospital and never raced triathlon again. The sunburn healed; the psychological scars never did.

Thankfully, most of us adopt a suitable pacing strategy to avoid this scenario, though why isn’t completely understood. Professor Tim Noakes suggests pacing ties in with his "central governor model of fatigue", whereby a subconscious mechanism in the brain draws on factors like experience, duration of exercise and environment to set a sustainable pace.

‘In fact, that’s where my model of fatigue derived from,’ Noakes once told me. ‘I realised there must be a regulator that slows people down in the heat to ensure they avoid heatstroke.’

Noakes suggests this psychological limiter is why we rarely experience heatstroke, though he recalled the case of a serviceman who died after marching in the heat for seven hours. ‘His rectal temperature was fine for five hours and then it went mad. Within 30 minutes he had heatstroke and then he passed away.’

Cases like this are at odds with Noakes’ model, which is based on maintaining homeostasis so you don’t overheat. Somehow, this serviceman overrode the internal warning signs until they became catastrophic. Thankfully, tragedies like this are a rarity but, says Cheung, remaining in the safety zone requires an individual approach.


An individual approach to heat management

‘There’s no single threshold core temperature that everyone is impacted or peaks at,’ he says. ‘In 2006, a study came out tracking runners at the Singapore Half Marathon.

They were acclimatised to the hot and humid environment and the researchers showed that, while all were over 39°C (over the resting norm of 37°C), some were over 41°C. But there wasn’t a case of one single temperature being problematic for everyone.’

Cheung’s undertaken studies where athletes have swallowed a pill that measures core temperature, where you can monitor the rise in real time. You can even train by core temperature. ‘Pills help because they give each athlete their own threshold,’ says Cheung. ‘If you do this, you must keep it individual.

Cheung’s key word is ‘acclimatised’. This is where a runner or rider trains in the heat to stimulate myriad physiological adaptations conducive to racing in the heat. ‘One of the key adaptations is that, over a period of time, core body temperature lowers by around 0.3°C, resulting in less impaired performance. I say “less impaired” because you’ll never match performance in cooler climes,’ says Cheung.

‘We also found acclimatisation results in a decrease in skin temperature, so it looks like it has a larger evaporative cooling effect, and sweat rate rose sharply, sooner – again for more efficient cooling. Heart rate came in lower, too, which is always a sign of adaptation.’

As for length of acclimatisation period, Cheung breaks this down into: short-term – fewer than seven days; medium-term – eight to 14 days; and long-term – over 14 days. ‘They all produce favourable results but, not surprisingly, the longer the better.’

A study by Danish researchers supports Cheung’s own work. The team took trained Danish time-triallists and had them ride 43km at 300w at a relatively cool 5°C. They then headed out to a training camp where daytime temperature ranged from 30-36°C, where they rode further 43km time-trials on day one, six and 13 of the 14-day camp.

‘On day one, they were about 85% of their performance level,’ Cheung explains. ‘By day six, that had risen to 92%. By day 13, it’d risen to 95%. This shows acclimatisation works.’


Heat acclimation at home

There are plenty of things you can do to acclimate to exercising in hot conditions back at home in cooler climes...


Create your own heat chamber

The first comes from a conversation I had with cyclist Michael Woods, who rides for the awkwardly titled EF Education First-Drapac p/b Cannondale.

We were chatting about January’s Tour Down Under, which often sees temperatures over 40°C. ‘How do you prepare for that sort of heat?’, I asked the Canadian.

‘In the past I’ve trained in Arizona before the Australian race, so it’s not too bad,’ he said, ‘but one year I’d been training in my European base of Girona. In January it’s really not very warm, so our head trainer set up a heat-adaptation tent for me at our Service Course.

It was a basic bike-show number where you could drop the canopy down. We had two Dyson fans on full heat blast, as well as a giant heat lamp that looked like it belonged to a Kenny Rogers Roaster. I went in there and cranked it up to 40°C and rode for 90 minutes every day for eight days. It made a difference from a heat-adaptation perspective. Other guys were really struggling at start of the TDU and I felt relatively comfortable.’

That might seem extreme, but it’s not beyond the realms of possibility to stick your turbo trainer in your small room, add a fan heater, crank up the radiator and get pedalling.

As an aside, if you're also seeking altitude benefits, you can go full Chris Boardman circa ’90s in the documentary ‘The Final Hour’, where he shows the cameras how he turned his daughter’s bedroom into a hypoxic chamber.

‘All the windows and doors have been sealed with tape,’ said Boardman, ‘and those three tubes are connected to a generator that reduces oxygen from 21% to 16%.’ You then have the sight of a heavily-sweating Boardman, dressed only in bib shorts, cranking out 400w to the backdrop of a fan and a shelf of children’s books including Dr Seuss’ The Cat in the Hat.


Have hot baths

‘Another option is to have a hot bath straight after riding in normal conditions,’ adds Cheung. ‘There’s research that shows this has a small adaption benefit.’

That was the conclusion reached by Neil Walsh of Bangor University, who showed that moderate exercise immediately followed by a 15 minute bath in 40°C waters over six days where ‘bath-time’ rose by 5mins each day resulted in a 4% improvement in 5km time-trial time in the heat.

The explanation for the benefits we see of taking a hot bath after exercise require further investigation but likely involve the combined elevation of core body temperature and skin temperature,’ Walsh said.

Arguably that’s impractical for recreational endurance athletes, albeit Walsh says you don’t need to bath every day. It’s certainly used by professional athletes though and we know for certain Tom Dumoulin at Sunweb has experimented with this protocol.


Train in extra clothing

More practical is the further suggestion that you should simply wear extra clothing during training runs or rides. ‘It won’t be as effective at raising core temperature as exercise in the heat, but it will deliver partial heat stimulus,’ says Cheung. 

Training for the heat is very much like training at altitude in that it stimulates physiological benefits designed to improve performance. Unlike altitude training, however, the benefits aren’t transferrable.

While elite athletes often head to the likes of Eritrea and Tenerife in search of rarefied air to boost physiological parameters like haemoglobin levels in the knowledge that this’ll pay dividends when back at sea level, acclimatising to the heat simply makes you a better athlete in the heat – there are no crossover benefits on return to cooler climes.

That Danish study I mentioned earlier showed as much, with their time-trial times when returning to Denmark being nearly exactly the same as before they went on their heat training camp.


Get fitter 

The fitter you are, the better you'll perform in the heat. As your fitness grows, you experience a host of adaptations that are naturally conducive to going fast in the heat. These include an improved sweat response to dissipate heat quickly and greater sensitivity of sweating response to increasing core temperature.

‘Improved aerobic capacity also leads to elevated plasma volume and cardiac output,’ says Cheung. ‘This minimises the competition for blood distribution between skeletal muscle and skin.’ In short, as Froome and Farah racked up the miles, their bodies developed a greater capacity for, and a slower rate of, heat storage.



The more experimental out there can also try out pre-cooling strategies like ingesting ice slushies before a high-intensity workout – again, something Sunweb do – albeit beware of an upset stomach.

There’s also research that shows perceptual cooling from menthol reduces perceptual thermal discomfort,’ says Cheung. ‘Again, though, I think this might be useful to for elite cyclists, but not for the general public. Ultimately, a focus on adaptation and a practised hydration strategy are the pillars to improve endurance performance in the heat.’

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