Running in hot weather safely

How to handle running in hot weather

Summer is the best time of year for the budding runner, but it can also be the toughest on the body with hot conditions making runs more intensive. Whether racing or just run training, it’s vital you stay safe in the sun, and handle the heat so it doesn't hinder your running techniques.

Culturally, sweat has been seen as a result of effort and therefore weakness. But truth be known, sweat is a runner’s best friend. Perspiration is our natural means of coping with body heat; the more we move the more we heat up and the more we sweat.

It is also an adaptive process where the more we exercise and run, the more readily our body will sweat to cope with heat. So, the more you run and fitter you get, the more you will sweat and the better your body will be at handling running this summer.

Handling the running heat
The body only learns to use sweat as a cooling mechanism, by having been put in a sweating position. Thus, the beginner or unfit runner does not sweat very readily, which on a hot day puts them more at risk of overheating. In extreme conditions the body can sweat so much that it uses up available fluids. No fluids, no sweat, no heat control, and the body’s core temperature very quickly rises to the point of heat exhaustion or worse, heat stroke.

The classic sign of heat stroke is that you actually stop sweating. The only treatment for this is to get out of the sun, cool the body with a cold bath or swim, and get fluids. Typically, the runner feels ill and is no longer thirsty; the body is shutting down and in extreme cases people will pass out. In this case medical attention is essential because the body’s core temperature must be regained.

Following extreme heat exhaustion or heat stroke many runners are never able to handle heat again. It’s as if the body’s defence mechanisms will not allow them to put themselves in that situation, so the best way to cope with it is to avoid it.

Staying hydrated while running
The key to the above is fluids, and lots of them. Perspiration may be the body’s way of dealing with the heat we generate, but it is also the main means of fluid loss during exercise. And fluid loss – or dehydration – is the most common reason why people under perform both in running training and racing.

The hotter the weather, the more our body sweats, which in turn means the more fluid we lose. When running, the average person loses 500 to 750ml per hour to sweat. In hot, humid conditions this can increase to well over a litre. But during exercise, and running especially, the stress on the gut means that most people can’t absorb much more than 500ml per hour. So on a hot day you’re always going to get behind.

Sports scientists measure the effects of fluid loss via weight loss during exercise. A litre lost to sweat corresponds almost exactly to a kilogram, and scientists say a 3 percent loss in bodyweight to sweat can result in a substantial loss of performance. For example, on a hot day a four hour marathoner might lose 4.5ltrs of fluid, but despite drinking at all aid stations they probably won’t absorb more than two litres during this time. That means a short fall of approximately 2.5 litres, which in an 80kg male is exactly 3%.

This applies equally in training, but can be avoided by making sure you’re well hydrated between runs. Fluid and fuel is absorbed approximately 30% more effectively in the 20 minutes following exercise. So, always eat and drink straight after running workouts and then try to get a minimum of two litres of fluid before your next run. Studies have also shown that the body absorbs water better when mixed with small amounts of carbohydrates, so try to make some of your fluid an energy drink.

Running under the sun
Because sweating is the body’s way of controlling heat build-up, most people feel more comfortable running in humid than dry heat. Actually, humidity is the far greater evil. In humid conditions the body sweats more to regulate core temperature, so you lose more fluid and run a higher risk of dehydration.

Even in moderate temperatures high humidity can be a problem because studies show that sweat rates are not substantially different once temperatures move above 20 degrees. So, runners in heavily humid conditions face almost as many problems in 25 degree heat as they do in 35 degrees.

However, as runners we are often more concerned with what’s happening inside our bodies than what’s happening outside. We ponder VO2max and hydration issues, but ignore the effects of exposure to direct sunlight. Under the ever-dissipating ozone layer summer running can become too much of a good thing.


The concerns range from chafing and dry skin right up to acne, eye damage, sunburn and skin cancer. Skin cancer, of course, is one of the world’s fastest-growing health issues, but runners should also be wary of bright UV rays and reflection. These can damage eyesight irreparably.

Strategies for summer runners
All of this is not to say that we shouldn’t be out enjoying running in the summer. Summer running should be embraced, just take a few basic precautions first.

The best time of day is in the morning. By avoiding the middle of the day you’re also avoiding the worst of the suns rays.

Regardless of when you run in summer, avoid eye damage by wearing sunglasses and a cap, and if you have fair skin cover up with thin, light coloured shirt. Avoid burning by wearing waterproofed (sweat proof) sun blocks with high SPF ratings, although runners shouldn’t lather sunblock on too thickly because there is evidence that sun screens can block pores, which could lead to overheating.

And while running in the heat generally means a loss in performance, we can train our bodies to cope with even the most excessive conditions. In the 1970s New Zealand’s Max Telford became the first man to run the 200km length of USA’s Death Valley, where the heat hovers at 50-degrees Celsius. Telford’s efforts opened our eyes to what the body could be trained to do and 30 years later hundreds of people have run the Badwater Ultra-race along the same course.

Now, no one is suggesting you try a 236km race in conditions so hot that support crews fry eggs on the road… Just that, with a few simple precautions the weather should never be a reason not to go running! Digg redditFacebook Stumbleupon