Is exercising in a heatwave a wise choice? This article by Peta Bee, published in The Times this week, looks at the pros and cons of exercising outdoors in hot weather conditions. It also offers some tips to stay cool should you wish to exercise outdoors.

How to work out in a heatwave

Think it’s cool to exercise when it’s hot? If you do, this is how to do it safely

Hot weather was once a reasonable excuse not to exercise outdoors. It was easy to convince ourselves that if we worked out, the sun would leave us puce and sweaty for hours afterwards. A deckchair and a glass of Pimm’s seemed a better idea.

Yet enduring the heat has somehow become a status symbol among those aspiring to improve their bodies. The expectation is that we will not only tolerate ferocious temperatures, but will embrace them by working out in sweat-wicking fabrics and air-conditioned trainers. It’s as though the higher the thermometer, the greater your perceived level of commitment.

Even on holiday, many feel the inclination to pack some fitness gear, just in case they can squeeze in a workout, whether it’s beach yoga or an arduous cycle ride on an unshaded mountain road. Last week a survey of more than 1,100 adults conducted by the retailer Ribble Cycles revealed that 74 percent of people would consider swapping their usual holiday for a fitness break, and one in three said they aim to increase their fitness when they are away.

Still, is it a good idea to put yourself through such sweaty effort? Professor John Brewer, the head of the school of sport, health and applied science at St Mary’s University, Twickenham, says that, with precautions and preparation, working out in the heat presents few problems — but it will feel like hard work.

“When it’s hot outside, the body requires much more effort to maintain its core temperature,” he says. “Sweating is your internal cooling mechanism, but the heart works overtime to divert blood to the skin so that heat can be dissipated as part of this process when temperatures are high.”

Trying to keep cool is an effort in itself. In a study carried out last year, Brewer put male volunteers through a series of running tests in his environmentally controlled laboratories that were pre-set to a warm 22.3ºC of a typical summer day and a cooler 8ºC of an average winter day. “Results showed that people found it up to 30 percent harder running in the summer heat,” Brewer says. “Their heart rates were about 6 percent higher than in the cooler temperatures and they sweat a lot more, both factors that can adversely impact performance.”

Not that it’s all bad news. Such is the scientific interest in hot-weather workouts that researchers have spent decades investigating the best ways to approach it. The consensus is that, as long as you acclimatise by gradually increasing the time you spend exercising in the sun, it is not only safe but beneficial. “Ideally you should train your body to dissipate heat more efficiently through incremental increases in exposure to the sun — a little bit extra time exercising in it every day,” says Greg Whyte, a professor of applied sport and exercise science at Liverpool John Moores University.

Studies at the University of Oregon show that athletes who train in the heat are better equipped to withstand a wide range of temperatures. “We know so much more about how best to prepare our bodies for exercise in the heat than a decade ago,” Whyte says. “We now know, for example, that pre-cooling can have a positive effect on reducing core temperature in the heat and that such approaches can improve endurance performance in hot conditions by up to 4 per cent.” Yet common sense should always prevail. “Avoiding the hottest time of the day is clearly very sensible,” he says.

And if all else fails? Pour water over your head when you get too hot. In 2012 researchers at the University of California asked a group of runners to wear heart-rate monitors and walk briskly on a treadmill for 90 minutes, then run 5km while in a laboratory heated to a tropical 32ºC and set to a low humidity of 30 percent. They repeated the trial several times — once with no fluids, another with chilled drinking water provided every ten minutes — and on a separate occasion the scientists doused the subjects with glasses of cold water every ten minutes, making sure it dripped down their faces and necks. In a final trial they had water to drink and had it poured over their heads.

Predictably, the lack of any fluids left the runners feeling hot and tired. When they were provided with water to drink, their heart rates lowered, but only when they had cold water thrown over them did they find the exercise test easier. Their skin temperature was lowest with the dousing and, importantly, they felt more comfortable.

None of the cooling strategies in that study improved overall performance — the runners completed their 5km run in about the same time whatever precautions they had taken. But that, Brewer says, is not the point. “What you’re trying to do in the heat is to minimise the discomfort you might feel. Whatever method you employ should have the goal of making your workout more tolerable. The battle is to keep your cool for as long as you can.”

Six rules to keep cool

Watch your fluid intake

Your sweat rate will increase in line with rising temperature. On average, the participants in Professor Brewer’s summer versus winter workout trial lost 1.3 litres of fluid after 40 minutes of simulated warm-weather exercise, 38 percent more than they did in the cooler “winter” climate. “Everyone has a different sweat rate so there’s no specific amount we advise people to drink,” he says. “Around 500ml of fluid an hour or slightly more during very hot weather workouts is a guideline, but the key thing is to drink when you feel thirsty.”

Fears about dehydration are largely overplayed, Brewer says. Unless you plan to exercise for more than 45 minutes, you don’t need to drink during your workout, however hot it is. “Make sure you sensibly hydrate before you head out by sipping regularly in the hours beforehand,” he says. “If you are out for a very long run or cycle you will need to replace the electrolytes, or body salts, lost in sweat, with a sports drink.”

Protect your eyes

People who work out in the sun without wearing adequate eye protection risk serious sun damage to their eyeballs, warns Henry Leonard, clinical and regulatory officer for the Association of Optometrists. “Most people know that overexposure to UV light can damage your skin, but a lot of people don’t realise that it can also affect your eyes. Exposure to UV light is associated with cataract formation and other conditions affecting the front of the eyes.” A good pair of sunglasses — CE-marked, with large lenses and a wraparound frame to stop light getting in at the sides — are recommended for any outdoor sport. “Even on a cloudy summer’s day, UV levels can be high,” Leonard says.

Take a hot bath

Last week one researcher suggested a novel way to prepare for warm-weather workouts: take a hot bath in the days before you leave for your holiday. Soaking in a tub heated to at least 40ºC daily after a workout in the weeks before you leave for a sunny climate could help your body to adjust to the heat, says Carl James, senior physiologist at the National Sports Institute of Malaysia. “It’s not necessarily an ‘easy’ option, but certainly easier than going into a heat chamber each day for 90 minutes, which is what athletes did previously.” He says that “getting some experience of being hot and sweating a lot before going on holiday would seem appropriate” for most people who plan to exercise abroad.

Or have a pre-cooling soak

Others have suggested pre-cooling by taking a cold bath. Last year a study at Australia’s Southern Cross University invited nine men to run in a laboratory heated to 33ºC with sensors attached to their bodies to measure core and skin temperature. The men were asked to run 5km without any preparation and then, a week later, to do the same after lying in a bath of tepid water (23ºC) for half an hour. In a final trial they spritzed their faces with cold water as they were running. Both of the cooling measures seemed to help — they ran significantly farther and faster after both the spritzing and bathing, although internal core temperature was lowest when they had taken a dip. In previous studies James has shown that pre-cooling with iced underwear enabled runners to improve their times in the heat by up to 4 percent.

Wear sunscreen and a hat

Anyone who exercises outdoors is at a higher risk of getting skin cancer than those who don’t. “It doesn’t matter if you are sunbathing or cycling,” says Dr Bav Shergill, a spokesman for the British Association of Dermatologists (BAD). “Spending time outside under the harsh rays of the sun requires protection.”

A study by dermatologists at the Medical University of Graz in Austria revealed that marathon runners had more solar lentigines, or age spots, caused by sun exposure, and more skin lesions suggestive of basal cell and squamous cell carcinomas. The most obvious reasons for the increased risk, the researchers suggested, was the amount of time the runners spent in the sunshine, that they ran in shorts and vests, and that half of them didn’t wear sunscreen. Wear a peaked cap, apply SPF50 sunscreen before you go and reapply an hour into your workout and then every hour thereafter, the BAD advises.

Drink a slush puppy

A slushy ice drink could help to lower your body temperature before a workout. “I’ve shown in studies that cold fluid ingestion — that’s any very cold, non-alcoholic drink — can offset the rise in core temperature that occurs when you exercise in hot weather,” Whyte says. “You need to be careful, though, as cold drinks can cause gastrointestinal upset for some people, so practise it a few times.”

The colder the better, if you can tolerate it. One New Zealand study showed that young male participants who drank a syrup-flavoured ice slush before running on a treadmill in a hot lab were able to keep going for an average of 50 minutes before they had to stop, compared with only 40 minutes managed by those who consumed a cold drink.