For some, running in the heat is a welcome experience, for others, it can lead to an uncomfortable run, a DNF or worse, illness. The heat can cause all sorts of issues for even the most seasoned runners and it is important to take the necessary precautions when you are planning on running, whatever the distance. We share some top tips for staying safe when running in hot conditions and ask when it could be considered too hot to exercise.

When is it Too Hot to Run?

Everyone is different – what is uncomfortably hot for one person is not so for another. That said, whether you can run comfortably in the heat or not, you really have to consider the impact on your body. Many suggest when the temperature rises above 80°F (27°C), it can become uncomfortable and potentially risky. Here are some citations to support this:

National Health Service (NHS) UK: The NHS advises individuals to take extra precautions when exercising in hot weather, particularly during heatwaves. They recommend avoiding strenuous physical activity during the hottest parts of the day and opting for cooler times, such as early morning or late evening, for outdoor exercise. Additionally, they emphasize the importance of staying hydrated and wearing appropriate clothing to prevent heat-related illnesses. (Source: National Health Service UK. “Heatwave: How to cope in hot weather.”

American College of Sports Medicine (ACSM): According to ACSM’s guidelines for exercise in hot weather, it’s recommended to avoid exercising outdoors when the temperature exceeds 80°F (27°C) due to the increased risk of heat-related illnesses such as heat exhaustion and heatstroke. (Source: American College of Sports Medicine. “ACSM’s Guidelines for Exercise Testing and Prescription.” 10th ed. Wolters Kluwer, 2017.)

Get Out for Earlier Runs

While you can’t control the start time of your race, you can choose to get out there and do your training runs early, before the heat gets too much. We like to get out and get it done early doors. Starting at 6am-7am, means you can get a few hours before you start to battle the heat. Of course, this won’t help you during an ultra when you will need to be acclimatised to running in the heat so give some consideration to doing at least a couple of your long training runs in the conditions you might face for a summer ultra. You can also use these opportunities to work out what chafes and what sort of foods you can stomach, plus how much fluid you need.

Also, keep an eye on the forecast for the week ahead. If experiencing a heatwave, plan the longer, harder stuff for days when the temperature may be lower.

Stay Hydrated!!!

First and foremost, hydration is critical. It’s not enough to hydrate the day before a race/training run or leave it to the day. You can’t start drinking more as you start to feel hot. Our bodies simply don’t work like that. You have to prepare sufficiently for running in the heat. Humans should be hydrating with 2 litres of water a day. This will need to increase during extreme temperatures and when you are sweating out more fluids due to exercise.

Preparation for longer runs is critical, especially when it comes to hydration which should begin days before, especially when preparing for an ultra distance. For a Sunday race, for example, we tend to start using electrolyte tablets such as SIS from the Wednesday. You only need it once a day but it’s good to get them in your system. It’s important to drink water too but too much water on its own will just flush the salts and electrolytes out of your system. So, drinking water at regular intervals is important but also make sure you are getting the electrolytes in. They say that your urine should be a light straw colour when adequately hydrated.

Even a five-mile run in temperatures above 30 degrees should be treated with respect. Take water with you and drink plenty when you have finished your run to replace the lost fluids.

Keep Hydrating

Keep drinking. Don’t just remember at the end of the day that you haven’t had any water then suddenly down a litre. Keep a bottle with you at all times. Drink whenever you can, right up to the run/race, during and after. Don’t wait until you are a few miles in. Drink from the start. It is recommended that you drink to thirst but we always take small sips of water at regular intervals. Running in the heat calls for some sort of backpack when running any distance. For shorter distances, you can often find water at church taps, seafront taps etc. We use a handheld bottle holder if going out for shorter runs in the summer.

If you have collapsible cups, like you will find at most races nowadays, you can pop them in your pockets or in your backpack/belt and use purification tablets to drink from natural springs too. Just be aware of where the water comes from and check that it is a natural source.

Electrolytes are Important When Running in the Heat

Make sure you have access to electrolytes along the course, or during your long training run. If you won’t get them at aid stations, fill one of your bottles with them. If you are using a bladder, take an additional bottle for them. You will need it. You are going to lose a lot of salt in the heat through your sweat and you need to keep putting it back in. Not only will you feel terrible if you are dehydrated, but the lack of salt in your system means you increase your chances of cramping. It is also worth considering salt tablets – take one before the race and pop one in your best for later on.

Wear a Hat/Visor

If you are running in the heat on a sunny day for a long training run or race, you could be out in the sun from anything upwards of 5 hours. We took around 12 hours to do our last ultra – it was hot and at mile 46, the nausea kicked in. Thankfully, I had a hat. Lightweight and white, this particular hat reflects the heat and covers the back of my neck. I didn’t wear it all day. Just when the sun was strong.

A visor is another alternative. It will keep the sun off your face although beware that it won’t keep the sun off the top of your head. With the sun beating down on your head for a long time, it is advisable to wear a hat. Again, if you are going to choose a visor, white is a good colour as it reflects the heat.

Iced Bandanas

Not sure how accessible these are on an ultra marathon route in this country unless you have a great crew but we’ve seen plenty of 100 mile Western States ultra-documentaries where they get one at every check point. If you have access to ice, you can also suck on ice chips which will help keeping cool when running.

We are talking about the UK here so it’s probably not readily available but don’t worry because the next solution should help!


Even now, after years of running, we can get a little complacent when the weather starts to turn. Only recently, I came back from a longer run with pink shoulders. The trouble with starting at 8am, is you don’t think you will need sunscreen but that time soon ticks by and the 10am sun can burn you. Be sure to put a liberal application of high factor sunscreen on before you head out of the door. You also want to think about carrying it with you in small bottle too as you will soon swear it out.

Dog Collars

Say what? Yes, you did read that right. Now, we haven’t actually tried this yet but we’ve recently seen it recommended in an ultra-group on Facebook and we thought ‘what a good idea’. So much so that we have ordered one to trial. These dog collars have technology that means you don’t need to refrigerate or freeze them, they have something in them that makes them cooling. Simply pop it around your neck but make sure you buy the right size.

Now, if at this point you are thinking you are going to look stupid with a dog cooling collar around your next, also consider that during an ultra, it doesn’t really matter what we look like and we are likely to have all sorts of more important things to think about.

Wet Running Buffs/Hats

If you should happen across a fresh water supply (stream, church, water station), soak a running buff in water and wrap it round your wrist or wear it round your neck. If you have a hat, head band etc. soak these in water too. It will give you some relief from the heat and a bit of respite. Top tip – if you do use a stream, like I did, don’t fall in! Wet feet weren’t part of my plan!

Make Sure You Have Access to Water During the Race

When you get to an aid station, chances are you will pick up a water bottle, fill up your collapsible water cup or have access to water. Drink some, throw the rest over yourself. Soak your hat in it if available. It’s worth checking with the race organisers what their aid stations are like and what water is available.

If you are running off-road, at some point you are likely to pass a village church or a stream of some description – don’t drink the stream water but by all means use it to cool off. If you are concerned about there being a lack of water, either ask someone to carry some and meet you or do water drops the day before. The ultras we have run have always been fairly close to home so we have been able to do water dumps in hedges. We have always passed by a village shop where we can use our phones to purchase water too.

Wearing the Right Clothing

Think about your clothing. You want wicking material that allows you to sweat without making you uncomfortable. Choose something that will keep the moisture away from your body. If you are going with a vest, make sure your hydration vest doesn’t chafe. If you are wearing a vest, be sure to wear sun cream. Your legs will be sore enough the day after an ultra without having to cope with sunburn too. P20 is a good brand of sun cream for those who sweat – it won’t slide off as easily as some traditional brands. You want to be comfortable but also protected. A hot sunny day will require the following:

  • Running vest
  • Hydration vest and plenty of water
  • Shorts
  • Hat
  • Sun cream
  • Bodyglide

If ever there was a time you were going to chafe, it’s when you are hot and sweaty. The only time I have every got chafing from a backpack is when running in extreme temperatures. It is so important to wear kit that is going to be comfortable. Plenty of Bodyglide on all the usual areas – between the legs, nipples for the men, around the sports bra bands for the ladies. Trust us, it will be so much more comfortable if you protect yourself from sunburn and chafing.

If you are new to ultra running, this is a hard lesson to learn. Once upon a time, some years ago, I signed up for the Palma half marathon. I hadn’t run in the heat before. I still have the chafing scars to prove I ran that race. I have never felt so sore putting a pair of jeans on to get back on the plane home and that was just a half marathon! Lesson learned – Bodyglide.

Expect a Change in Performance

Heat slows you down – fact! If you are expecting to knock out a PB on the hottest day of the year then you may want to think again. Don’t be surprised if you feel sluggish, lethargic, and can’t get your usual pazazz when racing. I have seen many try and fail long distances or spectacular performances because of the heat. I have seen a whole raft of participants come in much slower than they expected. Heat isn’t conducive to PB performances.

Recognise the Signs of Heat Stroke

If you should feel dizzy, nauseous, light-headed or generally unwell, call it a day. Don’t push it. Tone down the intensity of your runs and consider moving your speed sessions to another day. Keep an eye on your heart rate and be sensible. A run can always wait!

Respect the Heat

Finally, it is critical that you respect the heat. If it is eleventy billion degrees outside, stay home instead! Don’t run if you don’t have to. Missing one run on an extremely hot day won’t hurt.

The Hot Weather Checklist

  • Water!
  • Hat/Visor
  • Sunglasses
  • Sunscreen
  • Bandana/Buff for running under cold water or dipping in a stream

Do you have any tips for running in the heat? We’d love to hear them.