Comment s'entraîner pendant une vague de chaleur

Why is exercising in heat difficult?

The British summer is unreliable at best and while you keep your fingers crossed for sunshine, scorching temperatures can make l'exercice feel like a chore.

If you've ever struggled during a run on a hot, humid day, you're not alone. There are several reasons why exercise can feel harder when it is warm. The optimum temperature for your body is 37°C, but both exercise and hot weather increase your core temperature - especially when you combine the two at the same time.

You have several mechanisms to help you cope with heat stress. First, blood vessels dilate to increase blood flow to the skin, which allows excess heat to radiate away from your body. Then you begin to sweat which cools the skin and subsequently the whole body.

However, cooling down is more difficult in humid weather because perspiration doesn't evaporate as quickly from your skin. This means your body has to work even harder to cool itself, which raises your heart rate too.

In addition, excessive sweating can lead to déshydratation and salt loss. Around 60% of your body is water and it plays a key role in every bodily function. You can lose a lot of fluid when you exercise - as much as a litre or two an hour - mainly through sweating and breathing. You'll likely lose even more if it's hot and humid, which can deplete the fluid and electrolytes in your body. In turn, this can make you feel tired and sluggish as it becomes more difficult for blood to flow to your muscles.

Although it might feel challenging, it's important to stay active in the summer months. Not only is exercise good for your physical health, it decreases stress hormones like cortisol and increases 'feel-good' endorphins. Physical activity also stimulates the release of the brain chemicals dopamine, norepinephrine and serotonin, which play an important part in regulating mood.

"It is important to stay active all times of year, even when it's hot and you don't feel like exercising," says Peter Hopson, a personal trainer based in Leeds, West Yorkshire. "This is because, for fitness and health, consistency is key. If it's hot for days and weeks and you put off exercise until it's cooler, you may be undoing all the hard work you have put in to improve your health and fitness up to that point.

"It may also lead to you stopping exercise completely as you get out of the habit," he adds. "Once you've stopped it is much harder to get back going again. There are always ways to modify what you do in the heat."

Although exercise is important, being active when it's hot does come with more risks. "If you don't take reasonable precautions when exercising in the heat, the implications can be very serious," says Hopson. "Dehydration, sunburn and heatstroke are all common problems. These can lead to much more serious issues."

Dehydration means your body loses more fluids than you take in. If it's not treated, it can get worse and lead to serious complications such as heat exhaustion, heatstroke, seizures and kidney failure.

There's also a high risk of épuisement dû à la chaleur ou coup de chaleur during hot weather or exercise. Heat exhaustion can occur after you've been exposed to high temperatures and is often accompanied by dehydration.

In un coup de chaleur, your body can no longer cope. The normal mechanisms to keep your body cool stop working effectively, and your temperature soars to over 40°C. Symptoms include severe headaches, feeling or being sick, shallow and fast breathing, muscle weakness, fainting, confusion.

However by taking certain steps, you can mitigate these risks to stay healthy and comfortable when you work out.

Restez hydraté

Making sure you're well hydrated before you exercise is really important, especially in hot conditions. If you're dehydrated before you start exercising, your core temperature will rise faster and your heart will have to work harder than usual. The current guidelines advise drinking six to eight glasses of water or other non-alcoholic fluid a day, but you'll need to drink more if exercising. Do remember that coffee and tea up to 400 mg caffeine a day (about eight cups of tea or four cups of brewed coffee) contribute to your fluid intake, but very high levels of caffeine can dehydrate you.

The amount you need to drink will depend on how much you sweat and how long you exercise for. Other factors can include your fitness level, environment and the intensity of your workout.

"To mitigate the risks you can reduce the intensity and duration of your training, and ensure you're well hydrated before, during and after," Hopson says.

Try different types of exercise

If you're not in the mood to run when it's hot, there are plenty of other types of faire de l'exercice you can try. Try lower-intensity exercise, such as yoga or Pilates, or go on a walk to make the most of the clement weather.

"All varieties of exercises are great in summer," says Hopson. "You can take advantage of the warmer water with open water swimming, stand-up paddle boarding or kayaking. It's also great to take advantage of the nicer weather to get out hiking in the hills."

Avoid the hottest part of the day

It is often much cooler in the early mornings or evenings, so these can be a better time to faire de l'exercice. Avoid the midday sun (between 11 am and 3 pm), which is often the hottest part of the day.

"Try to stay in shady areas, like woodland or near buildings," says Hopson. "You can also use air-conditioned facilities. Most major gyms have adequate AC these days. Apply sunscreen if you're going to be in direct sunlight."

Cool down your skin

It's also important to think carefully about your clothing if you're exercising in hot weather. Loose, light-weight, sweat-wicking clothing can be more comfortable than tight sportswear. Remember, wearing black can often make you feel warmer too.

If you do feel too hot, applying cool water to your skin can help you feel better. Cold packs, cold wet towels or water sprays can help you feel more comfortable.

Take it easy

And remember, l'exercice can just feel hard sometimes - especially when it is hot and humid. Don't push yourself too hard and bear in mind that less can be more. "Most importantly be mindful of how your body feels and be prepared to cut your session short if needed," says Hopson.