How to manage running in the heat


Majell Backhausen is an Endurance Coach and Elite Athlete for Salomon, Suunto and Compressport and coaches athletes towards success in endurance trail running; educates people on the ‘why’ not just the ‘how’ behind training; and is an advocate for simplicity, patience and longevity in the sport of trail running and outdoor pursuits.

When you train in the heat, it's essential to be cautious. To stay safe and get the most out of your run, you'll need to understand how to prevent heat stress and your individual hydration needs.

Is it safe to run in high temperatures?

Running in how weather is not uncommon, with some of the most famous competitive highlights of the year taking place in places like Kenya, Ethiopia and across deserts. The Badwater event in California or the 4 Desert Grand Slam are some of the most renowned demonstrations of our ability to perform in extreme environments, while the 156-mile Marathon des Sables in Morocco sees competitors running in temperatures exceeding 50℃.

Australian Jacqui Bell is the youngest woman to have run the 4 Deserts Grand Slam. Watch her journey below or explore the full Finding Frontiers series here.

Finding Frontiers with Jacqui Bell


Hannah Moir, Senior Lecturer in Health and Exercise Prescription at Kingston University, has researched the effects of heat when running on the human body. 

"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."

Running in the heat and how you react to it is very individual. Everyone sweats different amounts, has a different sodium concentration in their sweat, and copes differently with the heat. Everyone has a different level of acclimatisation as a result of training and their everyday living conditions.

But one rule does apply to everyone: the best way to manage heat stress is to prevent it in the first place.

Preventing heat stress when running

When the heat increases, the two main things you need to manage is your body temperature and sweat loss.

Pay close attention to:

  • Hydration: Understand your personal sweat loss (more on this below) and reduce your depletion. Drinking water will keep you mentally sharper and more in tune with your body.

  • Clothing: Look for clothing which allows your sweat to evaporate — this has a cooling effect allowing you to better manage your body temperature.

  • Effort Level: Working harder will increase your body temperature, so maintain a pace that will keep you comfortable, even if it's slower than usual. Do not risk overheating. Once you go too far it takes a lot to reduce your body temperature again and it can be extremely dangerous.

  • Breaks: That said, stop for a break, let your body temperature and heart rate reduce, and make sure you stop in the shade, if possible.

  • External Cooling: Use water to splash on your skin and allow it to evaporate. This is how sweat works to naturally cool our bodies.

  • Time of day: Choose a cooler time of the day to run!

Understanding your hydration needs

Understanding your personal sweat loss, hydration needs and sodium requirements across a range of different environmental conditions is especially important for those training for competition or long-distance runs.

For more in-depth detail, I highly recommend reading and understanding the book: Sweat. Think. Go Faster, by Darryl Griffiths.

Calculating sweat loss

To calculate your personal sweat loss, follow these steps:

  1. Weigh yourself before a run with minimal or no clothing and record your weight.

  2. Note the environmental conditions experienced during the run i.e. temperature, humidity, altitude.

  3. Run for an hour non-stop, ideally at an intensity as close to a competition pace as possible. Use heart rate, pace or wattage to measure intensity.

  4. As soon as possible, weigh yourself in the same clothing as before your run and make sure you have dried off all excess sweat with a towel. Record this number.

  5. Simply take your weight before and after the run and place it into this equation:

    Weight Before Run (kg) - Weight After Run (kg) = X (kg) of sweat/hr


    82kg - 81kg = 1kg of sweat/hr. 1kg of sweat/hr = 1Ltr of sweat/hr. 1Ltr of sweat/hr = 1,000ml of Sweat/hr. Sweat loss per Hour* = 1,000ml *During the environmental conditions of the test

In the above example the sweat rate per hour is 1,000ml. This figure is the volume of sweat you lose based on the intensity and the environmental conditions the test is performed in. Remembering your sweat rate will change as intensity and the environmental conditions change.

You can perform this test in a range of different environmental conditions and build a record of how your sweat loss varies for cool to hot weather, different humidity and altitudes. This can help you to prepare for competitions with different environmental markers.

Heat management is about prevention. Calculate what your body needsHeat management is about prevention. Calculate what your body needs
Heat management is about prevention. Calculate what your body needs

Calorie expenditure

During this one hour test, you can also measure your calorie expenditure through a device like a GPS watch. This can help you to understand what calorie intake you need (based on the intensity of the test.) Knowing your calorie expenditure per hour provides you with the information you need to plan your calorie intake accordingly.

Your sweat rate, sodium concentration in sweat and calorie expenditure is very important information to have when planning a nutrition strategy. The longer you are out competing, the more important these numbers become.

Running in the heat brings different motivations to everyone. Some people love it, others hate it. Either way, it is guaranteed that we can never control the weather, only how we manage ourselves in the conditions