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Finlay McAndrew  •  Running Training •  26.06.2024 •  8 min read

How to handle running in the heat

Everyones perception of heat is different. This is because we get used to a set of conditions. For example, 20 degrees Celsius might seem relatively temperate to someone who is used to running in 28+ degrees Celsius. In contrast, running in 20 degrees Celsius will feel exceptionally challenging if you normally run in 10-12 degrees Celsius. 

The point were making is that theres no one specific temperature range that can be considered ‘hot’ when it comes to running. Running in the heat ultimately means running in warmer temperatures than youre accustomed to. 

Its essential to run in warm conditions throughout the summer if youre doing an autumn marathon or half marathon. This is for two key reasons. Firstly, this is when you should be doing your base miles and building up your aerobic fitness. If you don't run in the summer sun, you’ll probably find you’ve got a bit of a mountain to climb when it comes to getting ready for the race. Next, an autumn race could be hot, especially if it’s abroad. Training in warmer weather will improve your ability to tolerate it. Thus, improving your ability to perform in the event.

Female runner running in city streets in a sports bra and shorts

Why do we slow down in the heat?

It’s really simple. As your body temperature increases in the heat, blood is diverted away from working muscles to aid cooling. This reduces performance. Additionally, the plasma volume (water content) in the blood can reduce, which can compromise the power output of muscles.

Most importantly, our body will try to protect itself. Without getting overly technical, there is a theory that our brain effectively reduces our output if our core body temperature is rising to dangerous levels. However, the point at which this happens from runner to runner will vary significantly. Athlete’s such as Jonny Brownlee, who was famously carried across the line by brother Alistair at the Triathlon World Series in Mexico, had the ability to somewhat override this system. This can have catastrophic consequences. 

For most, a small (but significant) rise in core temperature will almost certainly result in an increase in perception of effort, a higher heart rate, and subsequent reduction in intensity. 

Male runner running with t-shirt tucked into shorts through an urban park

Training tips

If you follow a specific heat training protocol, and use tools such as the sauna, you might experience some of the following adaptations:

  • onset of sweating happens sooner to aid cooling;
  • sweat becomes more dilute (so you lose less salt and electrolytes);
  • your core temperature might not rise as quickly;
  • your starting core temperature might be lower (think of your core like a bucket, the deeper the bucket, the longer it takes to overflow); and
  • you’re likely to have a more positive mental attitude towards running in the heat.

A specific heat protocol is definitely something that performance-orientated athletes should be focusing on. For example, if you’re aiming to break 3 hours in a marathon, and it’s going to be warm, you need to consider how you prepare on all fronts. Either speak to a coach or sports scientist, if you’re looking for more advice on this. Universities often have environmental chambers and physiologists that can help guide you through the process too.

For those who aren’t going to attempt a heat training protocol, but would like to cope better in hotter conditions, simply running in the heat will help improve your performance. 

Training intensity guidance for summer runs

Don’t attempt your harder sessions in the heat. Running in hot conditions is an additional stress on the body. It’s likely you’ll compromise your progress if you try to overreach in an environment you can’t cope with. With that in mind, do your speed work in the morning or evening, when it’s cooler. Or look at the forecast and plan the session for more conducive weather. If you have access to a gym that is air conditioned, that’s also a good option.

You should start with easy runs in the heat, and adjust your pace so it’s slower than normal. Remember, the additional stress from the heat completely changes the impact of that ‘easy run’ on your system. This means it might take slightly longer for you to recover from the run, so consider how that might affect the training that follows.

If you start with short and frequent runs in the heat, you should start to notice some improvement in your comfort levels and perception of effort. This means you can start to build up the duration of the runs. It’s still a good idea to keep a lid on the pace, and run a bit slower than normal.

Female runner standing with arms stretched above her head in sports bra and shorts

What kit should you wear?

It may seem incredibly obvious to those who know, but light and highly ventilated running kit makes a big difference in the heat. Opting for ‘race’ fabrics is usually a good idea, as these fabrics are often very light and breathable.

Having said that, the Ronhill Tech Golden Hour Tee features a special fabric that regulates your temperature more effectively than traditional synthetic fabrics. The benefit of a running tee is that it protects your shoulders from the sun. When faced with identical conditions (heat and humidity), it’s easier to perform in cloudier conditions than when you’re exposed to the sun. This is the impact of solar radiation. Wearing UV protective kit can be more effective than having your skin exposed. If you do opt for a running vest, make sure you wear sun cream.

The other benefit of race-style kit is that it usually features less seams, and the fabric might even be laser cut. This can reduce the likelihood of friction. However, it’s always a good idea to put some Body Glide on in warm weather. 

A running cap can be the difference between you thinking the conditions are tough, but ok, to thinking it’s completely unmanageable. This is because it can reduce your perception of the heat, and keep the sun off your face. A similar thing can be said of running sunglasses. Reducing the glare of the sun may lead to you thinking it’s not quite as warm as it is.

Male runner sitting on steps holding a water bottle


We have the potential to cope with significant amounts of sweat/fluid loss. As you get more heat adapted, you’ll find you can cope with greater levels of dehydration, and it doesn’t have as big an impact on your performance.

Having said that, we obviously want to optimise hydration, and there are a few tips that you can follow:

  • Pre-hydrate before your run. Using an electrolyte tablet is wise, as they’re an anti-diuretic and increase your thirst sensation.
  • If you’re not used to running in the heat, carry water with you. There are lots of options, including handheld bottles, waist belts, and the increasingly popular hydration vests.
  • Rehydrate with an electrolyte tablet when you finish. Water moves to the highest concentration of sale, so plain water won’t hydrate you as well.
  • Drink more water than you think you need to. You don’t absorb all the fluid you drink, so you typically have to drink more than you’ve sweated out.
  • Avoid alcohol. It dehydrates you and will compromise your recovery on multiple fronts.

Summer running essentials

Recommended accessories to help you stay cool and train comfortably during warm and sunny spells:

Running in the heat ultimately means running in warmer temperatures than you’re accustomed to.

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