Analysis: the current heatwave means many runners may be asking if it's too hot for their daily outing

By Hannah Moir, Kingston University and Chris Howe, Kingston University

With the current high temperatures, people may find themselves questioning the safety of running in the heat. Running in hotter temperatures though is not uncommon, with many runners competing in warmer climates such as Kenya, Ethiopia and Japan, where temperatures average 25C.

But while running in the heat may be considered a risk to some people – such as children, the elderly and pregnant women – as long as precautions are taken, running in temperatures as high as 30-35C is fine.

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Time for a breather? Photo: Shutterstock

A number of running events take place in extreme heat (over 35C), such as Badwater, the 135-mile ultra-marathon that takes place in Death Valley, California, where temperatures can sore to over 50C. There is also the annual Marathon des Sables, a five-day run across the Sahara Desert in Morocco, where temperatures can reach 50C. This 156-mile run is considered the toughest foot race on Earth.

Our experience at Kingston University with people running and training in our heat chamber for events such as the Marathon des Sables and Badwater, demonstrates that with enough preparation, hydration and being sensible about how hard you run, it is possible to run safely in high temperatures. But it is important to note, that these races do take a lot of preparation and acclimatisation and running in such temperatures is certainly not recommended without thorough training.

Competitors on Marathon des Sables in the Sahara Desert. Photo: James Carnegie/Shutterstock

Running in the 30C heat does not come without its risks, it can very easily cause dehydration, overheating which can lead to muscle cramps, excessive sweating, headaches, nausea, tiredness and dizziness. Your performance may be impaired, and you may find you are not be able to run at the same pace or cover the same distance as you might having run in milder temperatures. Also, there can be serious health consequences to exercising in the heat, such as heat exhaustion and heat stroke.

But these can be avoided if you listen to your body and take sensible precautions to avoid getting too hot such as drinking enough fluids to stay hydrated, avoiding running at the hottest times in the day (between 11am and 3pm), wearing light, breathable clothing, and by slowing down your normal pace, and consider acclimatising to the temperature (which can take up to 14 days).

Running in the heat causes the body's core temperature to rise. The body works best when the core temperature is maintained at 37C, so to help keep the body cool, the body starts to sweat, allowing the heat to evaporate. This sweating causes water loss from the blood and can lead to dehydration.

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To help with the sweating, blood vessels dilate to allow more blood to be diverted to the surface of the skin by enabling more heat loss as a way to reduce this rising temperature. This is why people go red and their blood vessels may be more visible in hotter conditions. The issue is that less blood is available to be delivered to the working muscles, which in turn, puts a strain on the body, especially the heart. As a result, sweating can lead to dehydration and so exercising in the heat may make you feel tired and unable to exercise as well as you usually can at cooler temperatures.

The hotter the environment, the higher the dependency on sweating and heat loss to maintain the core body temperature. Typically, people will lose up to one litre of sweat per hour when exercising in hot environments, but it can be more than four litres of sweat in others.

The ConversationFor humans, though, one of the greatest things is that we are well designed at regulating our temperature compared with other animals. This enables us to run long distances in the heat. With regular exposure to high temperatures, the body learns to adapt, and the stresses and strains of running in the heat can be reduced. Adaptations to the body include increased sweat rates and blood volume, decreased losses of electrolytes (important salts and minerals) in the sweat, reduction in resting and exercising core temperatures as well as a reduction in heart rate and perceived effort levels when running in the heat. With preparation and common sense, you should be able to run safely in hot temperatures.

Hannah Moir is a Senior Lecturer in Health and Exercise Prescription at Kingston University. Chris Howe is a Senior research technician at Kingston University. This article was originally published by The Conversation.

The views expressed here are those of the author and do not represent or reflect the views of RTÉ