There’s no way around it, the world is getting hotter and heatwaves are becoming more frequent. When a heatwave strikes, your first port of call should be the local weather service, who can advise on when it’s unsafe to exercise outdoors. However, even when there are no advisories in place, running in the heat should not be taken lightly.
The easiest solution is not to run when it’s hot, but for many of us that’s no fun, and besides it’s not feasible if you’re following a running training plan for an autumn race. To help, we’ve sought expert advice to help you understand what running in the heat does to your body and how to mitigate the effects.
What You Need To Know About Running In The Heat
We begin with advice from Dr David Porter, a consultant in sports and exercise medicine at King Edward VII’s Hospital (opens in new tab) in London.
What are the dangers of running in the heat?
They start with simple dehydration where you feel a bit foggy or tired, and go to heatstroke and sunstroke at the far end of the scale, with people vomiting or passing out and ending up in hospital.
What are the signs to look out for?
For most people, the early signs are shortness of breath, some fatigue that you wouldn’t normally have, and excessive sweating. From an exercise perspective, you’re not able to do what you normally could. Some people might find that they’re drinking more than they would normally. If you’re starting to feel dizzy or faint, that’s the stage to stop and have a think about what you’re doing.
What sort of effect does heat have on the body when exercising?
It increases the impact on the cardiovascular system. You’re making it harder for the heart, and it’s also making it harder for the muscles to work – you are having to pump more blood to those muscles to generate the energy that you need. If there’s not as much blood going to the brain or some of the other vital organs when you’re running, that’s when you start to get that dizziness or fainting.
Are people able to adapt to the heat?
It is dependent on the person. Some of my colleagues have looked after football teams in Saudi Arabia, and the players are more used to very high temperatures. They normally train at the coolest time of the day, rather than the hottest for obvious reasons, but there’s no specific temperature at which you shouldn’t exercise.
How long does it take to adapt to hotter temperatures?
There is a bit of research out there on this. What you generally find is that elite athletes take less time to adapt because they’re used to a lot of travel and they adapt from country to country. Look at tennis players who move all around the world; European footballers move from high temperatures to low temperatures. It normally takes the average non-elite athlete probably between three and six months to adapt properly.
Is it possible to drink too much water?
Yes. When I was a junior doctor, working in emergency medicine and intensive care, I came across marathon runners who had drunk too much water during races and had put themselves into what is called a hyponatremic state – their sodium level had dropped. It changes the way your circulation works and changes the structure of the constituent parts of the fluid around your brain as well. That can lead to collapses, seizures, things like that. Hyponatremia is not a myth and deaths happen, but the majority of people wouldn’t be able to drink the sort of volumes that would get them to that state.
How To Cope With Running In The Heat
Running early in the morning or late in the evening is your best bet. If you have to exercise at lunchtime then swapping your outdoor run for an indoor swim, cycle or a run on a treadmill is a smart choice. When you are still running outside see if you can adjust your route so there’s as much shade as possible.
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No-one likes to hear it, but if the temperature is hotter than you’re used to it’s smart to dial your session back, especially if you’re dealing with a high training load because you’re following a marathon training plan. “People can mitigate their [physical] stress by reducing the pace at which they're running and/or reduce the distance that they're running as well,” says Porter.
Adjust Your Outfit
This doesn’t just mean sticking on a pair of sunnies (although that is a good idea). The temptation will be to wear as little clothing as possible, so a running vest is a good option, but remember to account for the risks of sunburn too and cover up if need be – especially when you’re going to be out for a long run – and slap sun cream on any exposed areas.
“Light, synthetic fabrics that wick sweat away from the skin’s surface will help lower your body temperature even on the hottest of days,” says Andy Page, Pure Sports Medicine (opens in new tab)’s strength and conditioning coach. “Avoid Lycra and compression garments because these can impair cooling.”
“It is very easy to dehydrate yourself by wearing layers that are too warm,” says Jason Taylor, running coach with we-run.co.uk (opens in new tab). “Also, ensure your clothes don’t chafe – use Vaseline if required. I would recommend a lightweight running cap. As well as helping to shade your face, this will keep the worst of the heat away from your head.”
“I wear white or light-coloured loose-fitting clothing,” says Merrell ambassador Dr Andrew Murray (opens in new tab), who has won races in the Sahara and Gobi deserts. “I will also wear sunscreen, and a Buff around my wrist to wipe excess sweat away.”
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Hydrate The Right Way
Remember you don’t just need water – you need electrolytes, too.
“Electrolytes are lost through sweat in significant amounts and must be replaced,” says Taylor. “Replacing electrolytes is essential to keep your body hydrated, enhance performance and help prevent muscle cramps.”
Sports drinks like Lucozade Sport contain electrolytes, and you can also use hydration tabs, which dissolve in water to create an electrolyte-rich drink. However, don’t just chug constantly during your exercise – there are risks to drinking too much water as well.
“Steady consumption of food and water on hot days, including using sports drinks, is a better strategy than trying to take on large quantities of water in a short time,” says Page.
Steer Clear Of Cramp
“Cramping is often a by-product of poor hydration and diet in the first place, so careful control of these factors will be key,” says Page. “Stay hydrated, ideally with a sports drink for the sodium, or eat a light meal with water two hours before you train. These are the most effective strategies for staying clear of cramp.”
Look After Your Feet
“As the temperature increases, your feet will sweat more,” says Taylor. “Make sure your socks fit well and are in good condition. If need be, tape any hot spots or use blister protection such as Compeed. Always lace the running shoe from the bottom up so it is snug, but not so tight it feels like a tourniquet.”
Rest And Recover
You will probably want to jump straight in a freezing shower when you finish your run, but a tepid temperature is the smart choice.
“After stretching, take a lukewarm shower to cool your core temperature but be careful not to go too cold because the shock will stop the body from cooling and make you shiver, which will actually raise your body temperature,” says Page.
And because running in the heat increases the demand on your body, you should increase your recovery time to compensate.
Jonathan Shannon has been the editor of the Coach website since 2016, developing a wide-ranging experience of health and fitness. Jonathan took up running while editing Coach and has run a sub-40min 10K and 1hr 28min half marathon. His next ambition is to complete a marathon. He’s an advocate of cycling to work and is Coach’s e-bike reviewer, and not just because he lives up a bit of a hill. He also reviews fitness trackers and other workout gear.
- Nick Harris-Fry Senior writer
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