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Running on a sunny day can be glorious, but it’s very easy to go overboard when running in the heat. It’s also important to keep safe if you’re planning on running while on holiday, especially if you’re heading somewhere warmer than our moderate UK climes. We asked our team of experts to answer our most frequently asked questions about running in the heat.

When’s the best time to run in the summer?

Most runners are already well acquainted with their favourite weather app. If the temperature is rising, now is a good time to become a morning runner. On really hot days, it can take a while for the temperature to drop in the evening so the early morning is often the coolest part of the day.

If you’re able to run early, set that alarm clock and get your run done as soon as you can. This can also be really helpful if you suffer from hay fever, as the pollen count is often lowest in the morning.

Do I have to run slower in hot weather?

Warmer weather will make your heart rate go up, even before you’ve got your running shoes on. You’ll need to adjust your expectations of your run as well as your session. If you’re heading out for an easy or steady run, focus on your heart rate or perceived exertion rather than pace. Your pace will be slower than usual, but you’ll still be getting all the benefits of the run.

If you had an interval session planned, there are several options. You can see if you can push it until later in the week when it’s not so hot. If warm weather is set in, it could be worth making the most of the gym’s air conditioning and doing it on a treadmill.

Long runs are the trickiest to plan for. Even if you get up super early, you’re likely to find yourself still running as the day heats up. This is a great time to use a walk-run strategy to help keep your heart rate down if you’re still out towards midday. And, of course, make sure that you’ve got a great running hat to keep you protected from the sun. Be extra aware of your body, and try not to push as hard as you would during cooler times.

How do I hydrate on hot runs?

“Sweating is one of the body’s primary means of heat regulation” says Registered Sports and Critical Care Dietitian, Tom Hollis. “Our sweat rate will of course increase as we train in the hot weather. This leads to rapid loss of hydration and electrolytes. It’s therefore essential to stay on top of this by consciously and proactively increasing fluid intake. This needs to be before, during and after exercise, especially on harder training days.”

The easiest way to do this is to invest in a great hydration vest. Don’t quite have the budget for that or don’t like to wear one? We’ve also had success planning a circular route around a corner shop or supermarket so that we can stop and hydrate en route.

Knowing just how much extra you need to be drinking can be tricky, but Tom has a solution. “One option is to weigh yourself before and after a session to get an idea of your typical sweat losses per hour in certain conditions. Otherwise you can respond to hydration cues, such as urine colour and volume. Pay attention to other symptoms of dehydration such as headaches and lethargy.

“If you know you are a high volume sweater or a particularly salty sweater (you have salty tasting sweat or salt residue on clothes), I would also recommend additional electrolyte supplements during the hotter months.”

Is it possible to drink too much water when I run?

Not to alarm you, but yes! As much as it’s important to stay hydrated, as we said above, glugging excessive amounts of water can cause hyponatremia. If you drink excessively, sodium levels will drop in the fluid outside your cells, and water will get in to try and balance the concentration of salt outside the cells. The cells then swell – including those in the brain.

This can cause vomiting, headaches, confusion, muscle weakness and even seizures. To avoid this, take on adequate water before you run, only drink when you feel thirsty during the run and consider a sports drink with added electrolytes for longer runs.

What should I wear to run when it’s hot?

What you wear on a run is a very personal choice. While some can’t wait to shed as much clothing as possible when the sun comes out, others prefer to cover up as much as possible. When choosing your outfit for your next run, think about what will keep you as cool as possible. Do balance this with keeping your skin from being exposed to too much sun. A lot of running kit these days comes with built-in SPF protection, which takes away the worry of applying sun cream to certain hard-to-reach spots.

A running hat or visor can help, as well as a pair of running sunglasses. And if you’re going to be taking extra fluid with you on a run, you might want to consider a hydration backpack. This is especially true if you’re training for an autumn marathon and doing long runs during the summer months.

Do I need to wear sun cream when I run?

Sun protection is important for runners year-round, but is vital during the summer. Choose a broad spectrum sun screen as these offer both UVA and UVB protection. UVB protection level is indicated by the SPF which ranges from 2 to 50+, while UVA protection is shown by the star rating out of five.

There are many brands that offer sun protection specifically designed for sports. This should make them more resistant to sweat. If you are doing a long run, you will need to reapply your sun protection during your run. Spray applications may be easier to reapply on the go.

Will my body adapt to running in the heat?

Bodies are clever and given time they can adapt to training in different conditions, including the heat. “For runners who successfully adapt and acclimatise to hot conditions, running in the heat can actually improve athletic performance,” sports physiotherapist Randall Cooper tells us. “The body learns to sweat more – and in turn improve thermoregulation, both in hot and cold conditions. Training in the heat can also lead to positive changes in blood plasma volume, reduce overall core temperature, reduce blood lactate levels and improve aerobic performance.” 

But, all these benefits don’t come easy. “It needs to be stressed that adapting to running in the heat should be done incrementally over many sessions. Not everyone responds to training in the heat in the same manner, so it definitely needs to be approached with caution.”

“The key to running in the heat is to start slow, and allow the body time to gradually adapt to the heat,” says Randall. “If you’re going for a 30-minute run, build gradually over the first 10 mins. This gives your thermoregulatory system has time adjust to the simultaneous stresses of the heat and exercise.”

Can I get heatstroke from running on hot days?

There are very real dangers to running in the heat, and it’s vital that you’re aware of the warning signs.

A heatstroke is a serious, life-threatening condition. The body tries to maintain an internal temperature of about 37°C and cools itself through sweating, faster breathing and dilating blood vessels. Running on very hot and humid days puts you at risk of heat exhaustion. Initially you’ll feel thirsty and have a high pulse rate which progresses to feeling nauseous, dizzy and irritable. Your body is trying hard to cool itself.

Untreated, this can progress to heatstroke where you can feel cold and stop sweating. A person with heatstroke may be confused, badly co-ordinated and possibly have a seizure. Urgent hospital treatment is needed so call an ambulance and cool them down while you wait.

It’s very important that you’re aware of these initial signs and know when to stop running – if your pulse rate is higher than usual and it’s a very hot day, don’t over do it.

The NHS has plenty advice on the signs of heat exhaustion and heat stroke as well as what to do if you suspect someone is suffering from it.

How do I cope with the heat during a race?

First of all, if you’ve been training during the colder weather and suddenly a heatwave is forecast for race day, you’ll need to adjust your expectations before you even start running. It’s just one of those annoying things that runners face from time to time. Aiming for the same time as you’ve been training for could result in you having to pull out of the race altogether with heatstroke or exhaustion.

OK, stern sisterly bit over! Now let’s focus on how you can get the best out of that race in the heat. You need to be well-hydrated before you set off – your urine should be pale yellow. Pre-cooling your body by sipping an ice-cold drink or crushed ice with water beforehand will also help to regulate your temperature.

A technique called palm-cooling can be beneficial during the race. It’s worth always taking advantage of water stations – even if you’ve got your own hydration pack on – to make sure that you stay hydrated throughout.

What do I do about my training plan runs if it’s too hot to run?

If the gym is an option for you – use it! We know that treadmill training can be dull when you’re covering long distances, and even more so when it’s lovely outside. But unfortunately it’s the only way to stay as true to your training plan as possible if running outside just isn’t an option.

As much as we runners like to stick to our training plan word-for-word, there is another approach. A large part of our training is all about getting our bodies used to moving for longer periods of time. If running feels a bit unmanageable but a long, gentle walk in the heat would work, you can absolutely do that instead. Aim to be moving for a similar amount of time that your training plan allowed for your run. You’ll still be making gains towards your goal, and you don’t have to abandon your plan for the few hot days.

How can I prevent prickly heat rash as a runner?

Prickly heat usually shows as an irritating rash on our skin, which flares up especially after we’ve been running in the heat. It’s usually caused by sweat ducts getting blocked. This traps sweat beneath our skin, causing little red bumps or blisters, which tend to be itchy.

Unfortunately, wearing sun cream designed for running can contribute to this. They’re often waterproof, to stop your sweat from running it off your skin. Make sure you shower as soon as possible after your run to help avoid this.