When we run in the heat, we sweat! This is the cooling mechanism to get rid of the heat produced by exercising muscles. But the heart has to work extra hard to send blood to the skin where it is cooled by sweat evaporating. So we use up lots of energy keeping cool that would otherwise help us run faster...no wonder when it's hot it can feel like running through treacle! 

As we run harder and exercise at high intensity, we sweat more, our bodies find is less easy to manage fluid passing from the stomach into the blood and we tend to lose our focus on drinking.  Over-heating and losing excess fluid may lead to dehydration as the body needs a good fluid balance to function properly. We need to make sure we're replacing lost fluid and salts contained in sweat. But it's not straight forward; some endurance athletes suffer from drinking too much water so the concentration of body salts becomes too dilute. This is a potentially serious, even life threatening, condition.

Top tips:

  • Remember that the body will get used to running in the heat and cool more efficiently, so give yourself a couple of weeks to adjust and dont push yourself too hard too soon.
  • For fear of stating the obvious, wear light coloured, wicking running gear. Sunglasses and a sun cap also help protect from the sun.  I recently ran a half marathon in a humid 26ºC alongside runners in gloves, jackets, long tights, and (I kid you not) one chap sporting a woolly hat. Rather than dressing to keep warm at the start, check the weather forecast and dress for the later stages of a run.


  • Pour water over your head, the back of your neck and your wrists to help cooling.
  • Finally, drink! Don't wait to feel thirsty ... regularly sip water or water with an electrolyte tablet (like Nuun) which adds flavour and valuable salts.