Friday, 20 April 2018

We are not camels. Managing racing in the heat.

Sheffield University Orienteering Club (SHUOC) on their way to smashing the Guinness World record for the half-marathon in one hour and forty minutes.

This Sunday is the 38th London Marathon and it's predicted to be one of the hottest. After the long cold winter this may pose difficulties for some runners.

These potential difficulties are linked to two factors: hydration and overheating.


We all know that we should keep well hydrated. Achieving this is not as simple as you might think. The ideal amount of fluid intake varies depending on the conditions and the individual. Drink too little and you might become dehydrated, too much and you become over-hydrated.

Both have medical and performance consequences and some argue strongly that overhydration has the far more serious consequences. Many people have died from overhydration in numerous situations including marathons.

Symptoms of dehydration
  • Feeling thirsty - this is the earliest and most prominent symptom.
  • Feeling weary, tired, weak
  • Feeling light headed and dizzy. These tend to present as the dehydration worsens. 
Managing Dehydration
  • If you start to feel thirsty or have a dry mouth - DRINK. But drink to thirst - don't overdo it. We are not camels.
  • How much depends on on individual factors but about 400-800ml per hour (about two cup maximum). 

Symptoms of Overhydration
  • Impaired performance
  • Sloshing in stomach or bloated feeling
  • Swollen hands, legs or feet (watch strap getting tighter, shoes tighter)
  • Nausea & Vomiting 
  • Headache. Note headaches are not a symptom of dehydration.

Managing Overhydration

  • Stop taking on more liquids
  • If you are concerned or start getting the more serious symptoms of nausea / vomiting / headache then go to a medical point.
Overhydration tends to occur in slower runners as they are out for a longer length of time and have more opportunities to drink greater volumes of fluids. 


For the vast majority of runners London won't be hot enough for serious over heating or heatstroke to occur .

Heatstroke occurs when the core body temperature rises to a level which is potentially very harmful. The main parameters governing this are speed i.e. energy required per unit time, and external temperature.

Heatstroke therefore tends to occur in very hot conditions and with faster runners racing over shorter distances (5-20 Km). The faster we run the more heat we generate.

In the temperatures at London the speed even the fastest runners race a marathon are unlikely to be be enough to generate the heat required to cause heat stroke. However, whilst very rare, there are documented cases of it occurring in some individuals at slower speeds and in cooler conditions.

Whilst heatstroke is very unlikely, there is a very high probability that many runners will struggle with the far less serious condition of heat exhaustion. Heat exhaustion is caused by external temperature rise i.e. on your skin. Your body does not like this and treats it as a warning signal generating symptoms in order to force you to slow down.

Heat exhaustion occurs when the body just isn't adapted to the hot conditions. This will be the case for the majority of runners on Sunday. Many runners will be physiologically incapable of handling the thermal load and may then experience symptoms of heat exhaustion.

Heat exhaustion is detrimental to performance but normally doesn’t lead to heatstroke as the conditions for the core body temperature to rise to critical temperatures.i.e. speed and external temperature, are not present.

Symptoms of heat exhaustion
  • Impaired performance
  • Fatigue
  • Headache
  • Dizziness
  • Short of breath
  • Nausea / vomiting
Managing heat exhaustion

  • Slow down - the slower you run, the less heat you generate the cooler you'll be. 
  • Use cooling techniques to lower your skin temperature - water over your head, cold drinks, ice, run in the shade etc. 


  • Stay hydrated but don't overhydrate - drink approximately 400-800 ml (1-2 cups) per hour during the race. 
  • Try to avoid getting too hot before you start - stay in the shade, put cold water over your head, on your neck or wrists.
  • If you know your not good in the heat consider starting at a more sedate pace then planned.
  • Keep as cool as possible during the race (shade, cold water over body, run through the cold showers provided.)
  • If you start to struggle - slow down, evaluate the cause - dehydration, over hydration, or heat exhaustion and act accordingly. If you are not feeling thirsty it's unlikely to be dehydration. 


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