My heart is racing. I’m dripping in sweat. It’s the hardest run I’ve done in a long time. It shouldn’t be, it’s only 5K – a distance I’ve done plenty of times – but never before in 40°C heat. I’d love to say it’s because I’m in some sunny destination but I’m not. Instead, I’m on a treadmill, inside a heated glass box, 60 miles south of Birmingham at the Silverstone race track.
There is (some) method to my madness. While I might not normally be tempted into exercising in these temperatures, competitors at the Paris Olympics are about to be tested by the weather and I’m keen to see how our bodies react to such climate extremes.
The 2021 Olympics in Tokyo were the hottest in history, with temperatures above 34°C and humidity approaching 70 per cent. Now, researchers are predicting that the Paris games, which begin on Friday 26 July, could be even hotter. Last month, a report titled ‘Rings of Fire’ warned about the potential risk to athletes over the coming weeks and said the Japanese tournament had given a “window into an alarming, escalating norm for summer Olympics”.
The researchers, from the British Association for Sustainable Sport and Frontrunners, highlighted how these hot temperatures might impact athletes, including making it more difficult to regulate their ‘core’ temperature, resulting in “compromised cardiovascular and muscle function”, “cognitive impairment” and dehydration. “These effects might be exacerbated in individuals with underlying medical conditions, as well as in some Paralympians, where their condition may affect their ability to thermoregulate… heat stroke can result: this is a serious medical condition that may have long term, multi-organ consequences and may even be fatal.”
Dr Jo Corbett, associate professor of environmental physiology in the School of Sport, Health and Exercise Science at the University of Portsmouth, explains further: “For athletes, from smaller performance-impacting issues like sleep disruption and last-minute changes to event timings, to exacerbated health impacts and heat-related stress and injury, the consequences can be varied and wide-ranging.”
Lord Sebastian Coe, president of World Athletics and four-time Olympic medallist, even went as far to say that climate change should be increasingly viewed as an “existential threat to sport”.
Preparedness for such events, then, is no longer just about training for your sport, but also about understanding how to cope in extreme temperatures. The Belgium field hockey team, for example, prepared for Tokyo using a heat chamber, describing how the gruelling simulated heat would mirror real-life conditions.
For most of us, the response to being too hot is to drink more water, but it’s not that simple. While water is important, so are electrolytes, which help regulate nerve and muscle function, hydrate the body, balance blood acidity and more. Drink too much and you can flush out those electrolytes, putting yourself at risk of a condition called ‘hyponatremia’.
“It’s incredibly dangerous to have a high volume of fluid intake,” explains Chris Harris, sports scientist at Precision Fuel & Hydration, where I’ve come to find out what heat does to my own body. “Your body either flushes it out or, if it can’t, water can end up damaging cells, causing toxin releases which can kill you.”
My 40 degrees run
I may not be an Olympian, but I was keen to learn how my body reacts in heat when it is being put through its paces. I agreed to undertake two 5K runs; one in ambient temperature and another in their heat chamber. I’m weighed and measured, don a heart rate monitor, then start my first run. My temperature and heart rate are recorded every five minutes, and I’m asked how difficult I’m finding things.
In the ambient temperature (18-19°C) my heart rate starts at 137 beats per minute (bpm) and by the end has risen to 147 bpm, while my temperature rises from 36°C to 36.5°C. It gets slightly harder as we go along, but I stick in their ‘steady’ bracket, not feeling I’ve hit ‘hard’ by the end.
Next up is my “hot run”. As I enter the specially-designed chamber at 40°C, I’m hit by a wall of heat and after just a few minutes’ running I’m at the same effort levels I reached at the end of the cooler run. My temperature soon starts to rise from the 36.2°C at which it started, as does my heart rate. It doesn’t take long to get into ‘hard’ territory, my breathing laboured and sweat pouring. By the end my heart rate has soared to 167bpm, my temperature is 39.2°C and I’m struggling.
I’m relieved to finish, but it takes a while to cool down and I continue sweating for some time after – a reminder that once you overheat, it’s hard to reverse. “When your body’s hot, you get these warning signs,” explains sports and exercise scientist Jack Wilson, like blurred vision and light-headedness. “So if you’re a marathon runner and start to feel that stuff, and you can see a competitor 50 yards up the road, now’s not the time to go chasing them. The advice to all of our athletes who compete in heat is, ‘don’t go past that threshold in the first place’.”
My data shows the effect of the heat clearly: a steep rise in temperature and steep heart-rate rise. Wilson explains that as my body sweats to cool me down, it’s diverting blood to my skin. The competition for blood supply between my muscles and skin creates more work for my heart, hence it feeling harder.
The team also calculated my sweat loss and predicted sweat rate using my weight and fluid intake pre and post-run, which means by combining this with my sweat test they can plan a ‘rehydration strategy’ for me, not only in terms of drinking more water, but replenishing electrolytes. Helpful for me, but vital if you’re a pro athlete hoping to win.
This is one strategy to help athletes competing in high temperatures, but there are other ways in which people can prepare their body for extreme heat. A key way is through acclimatisation – training in a hot country or taking advantage of a chamber like the one I’ve just been in.
For those of us without access to one, a hot bath or sauna combined with exercise – providing it’s done safely – can be an effective substitute, says Wilson. “If you went out for a run, got a good sweat on, then went straight into the sauna, the sauna keeps your temperature elevated so your body has longer exposure to elevated temperatures.” A similar tactic is wearing unbreathable fabrics, making it harder for your body to dissipate heat.
His final tip. “If you’re looking to really cope well with the heat, get as fit as you possibly can, get your cardiovascular system as good as possible, because the bigger the engine there, the better it can cope with that sort of challenge.”
Preparation is key, but with rising temperatures set to be an issue at all Olympics in the future – not just Paris – the Rings of Fire report also includes a broader range of recommendations for sporting authorities in a bid to protect athletes who are rightfully concerned about the environment in which they will be competing. These include: smart scheduling to avoid heat extremes and keeping athletes and fans safe with better rehydration and cooling plans, but also empowering athletes to speak out on climate change – as some are starting to.
For someone like me, having experienced exercising at high heat, I won’t be rushing to do so again. But with the Paris Olympics set to start next week, there’s not much athletes can do except to make sure they’ve prepared properly and to brace themselves for the added challenge. Good luck to them, I say.