How to exercise in a heatwave

Britain has experienced the hottest day of the year so far this week, and the Met Office has issued a yellow health warning meaning there’s an 80 percent chance of the current temperatures posing a risk to health.

And people who exercise outside should heed the warning more than most; “Regardless of how fit you are, exercising outside for longer than 45 minutes to an hour is going to pose a significant threat to your body this week,” says personal trainer Matt Roberts, who has worked with David and Samantha Cameron.

"Taking on fluid is probably the most fundamental part of exercising in a heatwave," says Matt. "As well as starting off hydrated, within the first half an hour you need to drink about half a litre of water and thereafter keep topping yourself up. If you're cycling, take a large bottle of water with you and plan a route where you know you'll be able to top up your bottle. If you're running, take enough water with you and don't run in remote areas where you'll be unable to top up."

According to Dr Andrew Murray,  a brand ambassador for Merrell who has won races in the Sahara Desert and the Gobi Desert (and became the first to run across the Namib desert  in the Namibian summer), you should be hydrated prior to starting exercise (aim for clear or straw coloured urine), and drink cold fluid during your run or cycle if you are thirsty. Fluid that has electrolytes and carbohydrates are ideal.

"Don't overdress," says Dr Murray. "I wear light coloured loose fitting clothing. I will also wear sunscreen, and a buff around my wrist, to wipe excess sweat away. Don't think about personal bests and I also try and run on the shady side of the road if there is one."

Dr Andrew Murray

Matt Roberts says exercising first thing in the morning and last thing in the evening is also a good idea; "That's not to say you can't run in the midday sun if you want to, or if that's where your lunch hour falls, but you'll wear out and dehydrate much faster in direct, harsh sunlight."

Overall, the experts say the key to exercising during a heatwave is to dress appropriately, drink plenty, avoid overheating and listen to your body; "Regulate heat by running slower: you control the heat you generate," says Professor Andy Lane, Professor of Sport and Learning at the University of Wolverhampton (he has run 15 marathons). "You will be breathing harder, and your heart rate will be higher for a similar speed in cooler conditions."

Important advice for keeping cool while exercising during a heat wave

Professor Sanjay Sharma, medical director of the London Marathon

Adapt your goal according to the conditions

If you're in training for an event, slow your planned pace this week. It's not a time to stick rigidly to a training schedule or aim for a personal best. 

Listen to your body

If you feel thirsty, drink water. If you feel overly tired, slow down. If you feel unwell in any way, stop. 

Wear the appropriate clothing

This should ideally be lightweight moisture management clothing designed for use in warmer conditions (but remember that new clothing can chafe if it hasn’t been worn and washed).

Drink, Douse, Drain, Drop

Drink if you feel thirsty and then douse your head and the back of your neck with the remaining water.

Don't forget sunscreen

This is vital. Apply a good quality sunscreen to all exposed areas before you leave home.