Running in the heat.

As runners we face many obstacles all year-round with heat being an inevitable and potentially harmful obstacle. But if we can understand how heat affects our bodies whilst running we can change our training methods, our choice of race as well as reduce the risk of harmful complications of heat stress such as heat cramps, heat exhaustion and heatstroke.

In order to understand how heat stress affects our running performance and how we can change our training and expectations to suit this, first we need to understand heat itself as well as our bodies natural responses to heat.

Heat includes many factors such as temperature, humidity and radiation all of which have profound effects on our performances. Heat loss usually occurs through many processes however, evaporation is the only effective process when the air temperature is greater than that of our body temperature.

When our bodies are exposed to high temperatures we rely on thermoregulation, which is the process in which the body works to maintain an optimal core temperature.  Our body mainly does this through perspiration which helps us to expel heat as our sweat evaporates. The amount of sweat evaporation depends on the level of humidity in the air because as humidity levels increase the amount of evaporation decreases and we expel less heat.  The downside to cooling through evaporation is the loss of fluid from the body, which places the body at risk of dehydration.

Fluid loss also reduces our blood volume which means less blood is being pumped out by our hearts and less blood reaches our working muscles, ultimately decreasing muscle function and negatively affecting our running performance. Heat also affects us by changing our perception of physical effort, because as temperature and humidity increases, we tend to think we are working much harder than we actually are, thus also affecting many runners on a psychological stand point.

6 Steps To Beat The Heat

  1. Body Acclimatization – by training in hot conditions we can create a demand on our bodies that leads to adaptations which can improve our ability perform in hot conditions. A minimum 6 runs in 2 weeks is required for our bodies to adapt, these changes include blood volume increases and efficient evaporative heat loss strategies.
  2. Ensuring Hydration – drinking 300-500ml of water over a 20-40 minute period prior to exercise should provide sufficient hydration without causing bloating. Drinking water whilst running should only be small amounts whilst ultra-distance runners should aim for a balance between planned intake of fluid and the amount fuel required for the race. It is important to keep in mind that drinking too much can be dangerous, therefore the general rule is to drink only when you start to feel thirsty.
  3.  Timing Your Runs – early morning or after sunset runs are usually the coolest part of the day. However, If your only option is to run during the hotter parts of the day, plan routes that have plenty of shade and water stops along the route.
  4.  Clothing – running with light and loose clothing facilitates evaporative cooling from sweat.
  5.  Training loads and intensities – decrease the distance of training runs and/or the pace of longer runs on hot and humid days. On pace focused training days find a shaded path which can be used for short interval training with longer recovery periods.  On non-acclimatization/extremely hot days an airconditioned gym with an assault air runner treadmill may be used, without negatively affecting acclimatization levels.
  6.  Listen To Your Body – run according to your perceived level of exertion and how your body feels rather than a pre-determined pace.


Magness, S. The Science of Running, (, 2014  3. Brooks, G. A., Fahey, T. D., Baldwin, K. Exercise Physiology: Human bioenergetics and its application, McGraw Hill, 2004.

Maughan, R. (2010). Distance running in hot environments: a thermal challenge to the elite runner. Scandinavian Journal of Medicine & Science in Sports, 20, pp.95-102.

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