Expert Advice For Running in the Heat

While it might be ‘winter’ here in Australia, the Northern Hemisphere is enjoying, or rather suffering in some considerable heat right now. Even as I finished my long run last weekend in the depths of the Yarramalong Valley on the central coast, I could feel it getting a little toasty to say the least. So just because it’s winter so to speak, doesn’t mean to say we shouldn’t be wary of running in warmer conditions. I’m sure many Aussies will be headed for overseas events where the temps will be getting high.

Lucas Trihey is no stranger to the risks that heat exhaustion bring when running ultras. He consults to many events in and around Australia. He’s very kindly allowed us to republished some of the extracts from his research in this post, helping us to understand the symptoms of heat stress and what to do about it.


Heat stress, heat injury and the effect it can have on participants in endurance events is potentially complex. While there has been some work done overseas, not much has been done in Australia in the context of recreational endurance activities.

Make sure you keep your core body temperature under control when running in hot weather
Make sure you keep your core body temperature under control when running in hot weather

Heat stress can affect anyone when environmental conditions cause a person’s core temperature to rise above normal. This is made worse when the person is exercising because the heat produced due to muscle exertion adds to the heat load on the body and if the heat accumulates at a greater rate than it can be shed the core temperature will rise. If heat stress progresses it can rapidly lead to serious heat injury and death.

So what causes heat stress? How do you reduce the effects of it and other related risks that need to be controlled, and how do you treat people?

What causes heat stress?

For endurance events, such as ultra marathons, any combination of environmental factors (high temperature, high humidity and solar radiation) along with prolonged or intense activity can cause heat stress in some athletes. Note that heat stress can occur on relatively cool days if a person overheats due to intense activity and is unable to cool down. Conversely, if environmental factors are very high people doing very little exercise can suffer from heat stress.

Related risks that need to be controlled

Dehydration – it is common in hot weather for participants to become dehydrated. Participants should be encouraged to drink when thirsty. Water should be readily available around the course, as well as sport drinks or a mix of water and sport drinks in recommendations for participants.

Hyponatraemia – There is a growing body of research that shows a link between over-hydration and hyponatraemia that can lead to a loss of body salts and illness caused by electrolyte imbalance. There may be a place for salty drinks or sport drinks in prevention of hyponatraemia.

Possible conflicts of dehydration and hyponatraemia – There are potential conflicts in education and management strategies for dealing with dehydration and hyponatreamia.  Education materials about “dehydration” should take care not to encourage gross over-hydration. “Drink if you feel thirsty” is a safe guideline to offer participants.

Symptoms of heat stress and heat injury can include:

  • Hot skin
  • Flushed appearance
  • Excessively sweaty or dry pale skin
  • Complaining of being too hot
  • Disorientation
  • Confusion
  • Dizziness
  • Irrational or unusual behavior
  • Inappropriate comments
  • Irritability
  • Headache
  • Inability to walk
  • Loss of balance and muscle function resulting in collapse
  • Profound fatigue
  • Hyperventilation
  • Nausea or vomiting
  • Diarrhoea
  • Delirium
  • Seizures
  • Coma
  • Sweating (too much) – profuse sweating on a humid day will cause high fluid loss.
  • Sweating (not enough) – if sweating stops the body’s cooling system is no longer functioning and overheating is imminent.
  • Chills and/or “goose bumps” skin

Treating a person with heat stress

A person suffering heat stress at any level must be stopped, cooled and monitored. If they complain of being “too hot” and exhibiting minor symptoms, such as hot and flushed skin, or dry skin, and a slightly elevated temperature, they should be sat in the shade and given cool drinks. Exercise must cease until they return to normal body temperature.

Understanding the symptoms of heat stress is important
Understanding the symptoms of heat stress is important

A person showing higher levels with more of the symptoms listed below can rapidly lead to serious heat injury, heat stroke and can rapidly become life threatening. These people must be actively cooled and monitored, or if exhibiting more advanced symptoms will need to be actively cooled and sent to hospital immediately.A person who has collapsed of heat stroke is a very serious medical emergency and needs to be aggressively cooled and evacuated.

Rapid cooling of patients

The absolute priority for a patient with serious heat injury is to rapidly lower the core temperature. The American College of Sports Medicine has categorised the effects of different cooling methods. The following methods are listed in order of most rapid to slowest:

  • Cold water and ice water immersion (using a small tub or similar).
  • An aggressive combination of rapidly rotating ice water-soaked towels to the head, trunk and extremities and ice packs to the neck, arm-pit and groin.
  • Ice packs to the neck, arm-pit, and groin.
  • Warm air mist and fanning techniques provide slower whole body cooling rates and are most effective only when the relative humidity is low. (ref Armstrong et al ACSM)

Are certain body types affected?

It’s true that certain body types are affected by heat stress more than others i.e. those with a higher mass can be more susceptible. Excess adipose tissue (body fatness) limits the rate of heat loss. From my observations there seem to be many people who are carrying additional weight in the form of adipose tissue tackling long endurance events when their fitness has not prepared them for the event.

Clothing Advice

Loose, light coloured, airy clothing will help the body to stay cooler for longer, whereas dark, tight clothing will retain heat. Appropriate clothing is also very important – minimal clothing with the textile fibres being hygroscopic and loose fit (i.e. not lycra or cotton). Event organisers should also encourage participants to wear light-coloured, loose and airy clothing on hot days and to avoid tight garments, lycra and dark colours.

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Dan
I'm a mediocre runner who can bat above his average when I train hard. A man of extremes, I do enjoy everything life offers and consider it an absolute pleasure just to be able to put one foot in front of the other and let my mind wander somewhere different.

5 thoughts on “Expert Advice For Running in the Heat

  1. I wonder what Lucas’ view would be on the X-Bionic Fennec shirts, which are tight and are supposed to be good for cooling. I’ve worn one here a few times in hot 30+ weather and it seems to do what it says on the packet and is cooler than my normal running shirts.

  2. Is there a correlation between increased heart rate and temperature or is it humidity? I was running in 30C temps with 90% humidity the other day and noticed my heart rate was about 10bpm higher for the same pace on the flat.

    Does the heart work harder to pump blood to the skin surfaces for heat loss, or is there less oxygen in air with a higher humidity?

    Thanks for posting!

  3. Andrew; yes HR climbs with heat as a result of dehydration due to decreased blood volume, making blood harder to pump therefore increasing heart rate to compensate…among other physiological phenomena.

    Don’t do heart rate testing in the heat, the results will be skewed!

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