Heat exhaustion

The effects of heat exhaustion on the body and the pathology of resultant depleted physical output. (A fairly accurate scientific waffle-fest by some fell runner).

So why does getting too hot screw you up? What's going on, and why did I turn into an 18st jogger when I got very hot at alderman's?

As far as I can tell it's down to Hypovolemia which is decreased blood volume, a decrease that is down to water loss due to sweating. The big hitter for fell runners encountering this condition is that vascular dilation occurs. The body shuts down blood supply to extremeties in order to preserve the vital organs, which is remarkably similar to cold shock, and cell osmosis is also impaired. There is a whole gamut of other nasty effects, but I've singled out Hypovolemia because it slows you right down to a stagger.

The reason you can't get up a hill in hot conditions is basically because your body is shutting down blood supply to your legs, and when exactly this happens is different for everyone due to heat acclimation and your body's thermal efficiency. So big lads carry more heat than racing snakes in other words. The issue of salt loss is to me relatively insignificant compared to the onset of progressively deminishing cardiovascular performance. As soon as you take water on board, Hypovolemia decreases and you get your legs back as a direct result of blood vessels opening up.

This is a process that soldiering on will intensify very quickly, to the point of syncope (fainting) when your body stops you running by impairing your brain function and cognitive ability. At this level, all blood is directed to major organs so that multiple organ failure does not occur, and you end up bollocksed on the floor.

The only way to save yourself this prognosis is to either stop for water or carry it with you. Everyone's Hypovolemic trigger point will be different.

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Originally Posted by mr brightside

The reason you can't get up a hill in hot conditions is basically because your body is shutting down blood supply to your legs, and when exactly this happens is different for everyone due to heat acclimation and your body's thermal efficiency. So big lads carry more heat than racing snakes in other words. The issue of salt loss is to me relatively insignificant compared to the onset of progressively deminishing cardiovascular performance. As soon as you take water on board, Hypovolemia decreases and you get your legs back as a direct result of blood vessels opening up.

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It may (or may not) be illustrative that 7 out of 79 women retired (starting at 11am) but only 3 out of 222 men starting at 1pm when presumably it was much hotter.

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Originally Posted by Graham Breeze

It may (or may not) be illustrative that 7 out of 79 women retired (starting at 11am) but only 3 out of 222 men starting at 1pm when presumably it was much hotter.

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I think a factor in those numbers you refer to Graham is that before the men's race started reports from the women about the heat reflecting from the ground, especially on the ascents, and the condition of some of them at the finish made many of the men, including me take on more water than normally would be the case. Some were even jumping in the canal to cool down prior to the start.

I do not know what advice regarding hydration was given to the women prior to their 11am start by the organisers as I was not there but before the men's start at 1pm there were repeated announcements to hydrate and to carry water, which is not usual for a 5 mile race.

I think the RO and his team should be applauded for their efforts and for the copious supply of water available both prior to and after the race. I could have done without the jug of electrolyte poured over my head at the end though!

Terminology: the term Heat Exhaustion is rarely used in the current literature - it confuses the issue by making people think it is a different illness from Heat Stroke - whereas of course Exertional Heat Illness is a spectrum, with Exercise Associated Collapse at one end, and Exertional Heat Stroke at the other.

Exertional Heat Stroke - EHS - has 2 diagnostic criteria - 1/ a core temperature above 40 C and 2/ CNS dysfunction - this can be dizziness, collapse, confusion, fitting, aggression, hysteria, coma and so on. The skin can be anything from drenched to dry - there is a common misunderstanding that for EHS to be diagnosed sweating must be absent.

Like in cardiac arrest, where instant CPR is the gold standard treatment, by bystanders if need be, in EHS cooling by CWI - Cold Water Immersion - or rotating drenched towels to all skin - is the gold standard - before transport. Fans/cold packs to axillae/groin/neck are not good enough.

In the field of course the collapsed confused runner may have EHS, but the possibilities also include hypoglycaemia, a cardiac event, hyponatraemia, head injury, stroke - the list goes on - and the chances are a rectal temperature probe is not available. In EHS aggressive cooling is needed within minutes - maximum 10 - rotating drenched towels or clothing is the most likely available cooling method - a stream/tarn might be nearby but the risks with a combative/confused/comatose person are high. If someone develops EHS on the fell I just hope someone with knowledge of the various possibilities and how to treat them is involved in their care!



From the prevention point of view, whilst dehydration is to be avoided, so is over hydration, so drink to thirst applies. Acclimatisation to exercising in warm/hot conditions is also important, and has been shown to be helpful.



It would be interesting to know how many cases of EHS have occurred in fell running. I have seen a couple of cases of EAC - Exercise Associated Collapse - in my running career, on hot days (in UK terms). They recovered fairly quickly - half an hour or so - with rest/shade/drinks.

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Originally Posted by Llani Boy

I think the RO and his team should be applauded for their efforts and for the copious supply of water available both prior to and after the race.

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I totally agree.

In fact although the pre-race notes said water would not be provided on the course in fact, as you know, it was.

I have nothing but praise for the RO and his team.

At the Welsh 1000%, 31 people retired from long race out of 171 (18%)

Interesting re the ladies... only 4 ladies retired... although that still equates to a similar amount in percentage terms (4 out of 21 ladies, being around 19%).

I wonder if some of the cases at Aldermans Ascent were more severe due to the shorter, more intense nature of the race compared to W1000. The Aldermans race being 30-60mins for most, with the best will in the world, most people are going to run that hard, however dire the conditions and warnings.

On the W1000 it was obvious that much more preservation was required over a period of 4-7hrs, and people were more inclined to run accordingly...?

A friend collapsed at the Tal y Mignedd a few years ago in the extreme heat. His symptoms included confusion, aggression, collapsing. I saw him about an hour later while he was sitting in a stream and he was fine again. It was very worrying at the time for those who saw him in the worst of it.

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Originally Posted by Mike T

Terminology: the term Heat Exhaustion is rarely used in the current literature - it confuses the issue by making people think it is a different illness from Heat Stroke - whereas of course Exertional Heat Illness is a spectrum, with Exercise Associated Collapse at one end, and Exertional Heat Stroke at the other.

Exertional Heat Stroke - EHS - has 2 diagnostic criteria - 1/ a core temperature above 40 C and 2/ CNS dysfunction - this can be dizziness, collapse, confusion, fitting, aggression, hysteria, coma and so on. The skin can be anything from drenched to dry - there is a common misunderstanding that for EHS to be diagnosed sweating must be absent.

Like in cardiac arrest, where instant CPR is the gold standard treatment, by bystanders if need be, in EHS cooling by CWI - Cold Water Immersion - or rotating drenched towels to all skin - is the gold standard - before transport. Fans/cold packs to axillae/groin/neck are not good enough.

In the field of course the collapsed confused runner may have EHS, but the possibilities also include hypoglycaemia, a cardiac event, hyponatraemia, head injury, stroke - the list goes on - and the chances are a rectal temperature probe is not available. In EHS aggressive cooling is needed within minutes - maximum 10 - rotating drenched towels or clothing is the most likely available cooling method - a stream/tarn might be nearby but the risks with a combative/confused/comatose person are high. If someone develops EHS on the fell I just hope someone with knowledge of the various possibilities and how to treat them is involved in their care!



From the prevention point of view, whilst dehydration is to be avoided, so is over hydration, so drink to thirst applies. Acclimatisation to exercising in warm/hot conditions is also important, and has been shown to be helpful.



It would be interesting to know how many cases of EHS have occurred in fell running. I have seen a couple of cases of EAC - Exercise Associated Collapse - in my running career, on hot days (in UK terms). They recovered fairly quickly - half an hour or so - with rest/shade/drinks.

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What about the dramatic decrease in physical performance, are reduced cardiac efficiency and shutting down of blood supply to the limbs to blame? Assuming of course that your energy and salt levels are ok, which they should be for a short race.

I'm just thankful it's going to be cooler and probably a lot wetter at Turnslack. I scored 65 50@50 points at Aldermans...so i guess that one is going to be a commemorative garment counter, not a points counter.

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Originally Posted by mr brightside

What about the dramatic decrease in physical performance, are reduced cardiac efficiency and shutting down of blood supply to the limbs to blame? Assuming of course that your energy and salt levels are ok, which they should be for a short race.

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The problem the body faces in Exercise Associated Collapse is using a limited resource - blood volume - to do three essential tasks - to go to the skin to lose heat (via dilated blood vessels and sweating), to go to the muscles to provide O2 and energy and flush away waste products and CO2, and to go to the brain to maintain consciousness. If people push themselves hard in the heat then eventually there is not enough blood to do all three of these tasks - and they grind to a halt, and may collapse as their blood pressure is too low.

Acclimatising to exercising in the heat results in an increased blood volume, as well as an increased sweat rate with a lower salt concentration.