Cycling UK Forum

I'm one of those who don't drink a great deal - usually about two litres for a 200k audax on a hot day - I have suffered from exercise induced nausea from school days and I can't stomach large amounts of liquids while riding.
I usually ride with one bottle of electolyte drink and one of plain water.
On this subject - I was riding an audax some years ago and at one of the cafe controls I came across a clubmate who was feeling unwell.
When he got up he nearly fainted. We helped him outside - it had been a hot day and he had consumed "plenty" of liquids.
I got him a glass of water with a teaspoon of salt in it and got him to take sips. After a few minutes he was feeling much better.

Sweep wrote: ↑11 Jul 2022, 8:33am ...
Question - is this "wet bulb" temperature the same as you get on some weather sites listed under the nominal temperature as "feels like", as on met office site:

https://www.metoffice.gov.uk/weather/fo ... 2022-07-11

(click on "show full forecast" at the bottom and it shows this under the nominal temp)

They're not the same but they are closely connected. Wet bulb temperature is affected by relative humidity. Calculation of the Met Office's "feels like" temperature uses air temperature, relative humidity, and wind speed.
https://blog.metoffice.gov.uk/2012/02/1 ... mperature/

Jonathan

Jdsk wrote: ↑11 Jul 2022, 9:34am

Sweep wrote: ↑11 Jul 2022, 8:33am ...
Question - is this "wet bulb" temperature the same as you get on some weather sites listed under the nominal temperature as "feels like", as on met office site:

https://www.metoffice.gov.uk/weather/fo ... 2022-07-11

(click on "show full forecast" at the bottom and it shows this under the nominal temp)

They're not the same but they are closely connected. Wet bulb temperature is affected by relative humidity. Calculation of the Met Office's "feels like" temperature uses air temperature, relative humidity, and wind speed.
https://blog.metoffice.gov.uk/2012/02/1 ... mperature/

Jonathan

thanks - being a thicko until recently I never quite understood until recently someone I know from a hot bit of the planet saying that they suffered more when it was humid (I think I thought - moisture good) - only just twigged that high humidity causes problems with you clearing sweat/cooling your body.
I checked out their bit of the world on that Met Office site and whereas here in the UK, the "feels like" is usually below the nominal temp, there it is quite common for the "feels like" to be ABOVE!!!!
no wonder they have probs - me too having spent two summers there and once when young getting something that was as close to heat stroke as I would like to get.

I have played football in 40 C, worked in agriculture in similar temperatures, and worked in the desert in the USA. I have not, that I am aware, suffered heat exhaustion, even though I don't really like the heat.

We were always told not to drink sugary drinks, like sports drinks, as this can make you lose more body fluid, but to drink water (not too cold) and add electrolyte drops or tablets to every third or fourth drink (the ones with salts in are best). They also said, at least 1/2 litre of water per hour, when exerting yourself. That's a rule of thumb, and an individual may need somewhat more. But as noted above, don't drink too much without replacing salts & electrolytes.

Bananas and potatoes (or sweet potatoes) are good snacks for the potassium, and slow release carbs. And, as others have said salt is important, too.

axel_knutt wrote: ↑10 Jul 2022, 1:55pm

Cugel wrote: ↑10 Jul 2022, 9:43amIf its also humid, you may find you can't sweat to lose body heat as easily as you normally do.

A wet bulb temperature of 35C is the limit to human survival:
Wet Bulb.png

thanks for the simple chart - it sure does show that at 40 degrees or approaching you had better keep a close eye on that humidity figure.

Psamathe wrote: ↑10 Jul 2022, 11:26am From a non-medical perspective I think different people tolerate heat and it's effects differently. From my various travels I seem to handle heat a lot better than many others i.e. on quite a few occasions others really suffering whilst I'm only beginning to show maybe initial signs.

I don't know about individual physiological variations in tolerance... and once upon a time I was involved in deliberately heating people up to see what happened!

But the most important ways of increasing tolerance are behavioural, and those can be learnt. And of course there are particular risks when we *move into other environments where we don't know the tricks. Cycling in an unfamiliar environment is wide open to those, and having an external target to meet rather than resting in the shade with the locals can be the last straw,

Jonathan

* As with the discovery of vitamins!

Vorpal wrote: ↑11 Jul 2022, 10:01amWe were always told not to drink sugary drinks, like sports drinks, as this can make you lose more body fluid...

I don't know of a physiological mechanism that would do that. For most people the renal threshold for glucose is too high for osmotic diuresis to occur.

But the promotion of "sports drinks" is probably one of the major reasons that overhydration occurs. And, as above, that can cause serious problems.

Jonathan

foxyrider wrote: ↑10 Jul 2022, 9:09pm (snip)

As regards hydration/cooling effects, a cold beverage does give immediate gratification but i find hot tea has a longer lasting effect, i'll often have both when i stop on a hot day like yesterday. When i get home i'll generally have an electrolyte drink - not an energy drink perhaps followed by more tea! I know if i've not got things right as i'll get cramps, something i seem more prone to since my DVT 5 years ago.

(snip)

I recall seeing a demonstration (and explanation) of how the temperature of a cool-down's process can have counter-intuitive effects. The fundamental mechanism at work seemed to be that if you employ a very cold medium in trying to reduce your body temperature, you can inadvertently invoke the bodily responses that automatically deploy in trying to keep you warm! And vice-versa! Oo-er.

If you come out of the sea cold and have a hot shower in an attempt to warm up, your body goes, "It's hot out there" and pops out your veins etc. as its normal means of cooling in a warm environment. Meanwhile, your core is still freezin'.

If you drink ice cold fluid when hot but in the shade, your body can assume its generally cold, so it operates body responses for dealing with cold environments, perhaps reducing your sweating and drawing in your surface veins, so you can't cool as quickly.

Of course, this is just a hazy recollection of "stuff I once read". But Jonathan will be along in a minute with links to five scientific papers of only 23 pages each to give us the accurate picture.

Cugel

Jdsk wrote: ↑11 Jul 2022, 10:05am

Psamathe wrote: ↑10 Jul 2022, 11:26am From a non-medical perspective I think different people tolerate heat and it's effects differently. From my various travels I seem to handle heat a lot better than many others i.e. on quite a few occasions others really suffering whilst I'm only beginning to show maybe initial signs.

I don't know about individual physiological variations in tolerance... and once upon a time I was involved in deliberately heating people up to see what happened!

But the most important ways of increasing tolerance are behavioural, and those can be learnt. And of course there are particular risks when we *move into other environments where we don't know the tricks. Cycling in an unfamiliar environment is wide open to those, and having an external target to meet rather than resting in the shade with the locals can be the last straw,

Jonathan

* As with the discovery of vitamins!

agree - this is of course the "mad dogs and englishmen" thing.
Locals in hot places do use the shade - not unusual to see them cross the road to walk in it.
I used to lead lots of london rides and a southern italian chap was a regular - on one ride an habitually intellectually arrogant chap said - "i don't know what sort of italian *** is, but I noticed that whenever we stopped for a rest he went under a tree for some shade". Doh!
I did once in southern italy ride for about 45 mins in a temp close to 40 - I noticed some rather odd things happening before i eventually got to the place under the seaside palms where i was meeting some folk.
My skin seemed to develop small bumps - something to do with trying to shed more heat?

all returned to normal on getting under the trees and some water and cheap wine.

Cugel wrote: ↑11 Jul 2022, 10:12am

foxyrider wrote: ↑10 Jul 2022, 9:09pm (snip)

As regards hydration/cooling effects, a cold beverage does give immediate gratification but i find hot tea has a longer lasting effect, i'll often have both when i stop on a hot day like yesterday. When i get home i'll generally have an electrolyte drink - not an energy drink perhaps followed by more tea! I know if i've not got things right as i'll get cramps, something i seem more prone to since my DVT 5 years ago.

(snip)

I recall seeing a demonstration (and explanation) of how the temperature of a cool-down's process can have counter-intuitive effects. The fundamental mechanism at work seemed to be that if you employ a very cold medium in trying to reduce your body temperature, you can inadvertently invoke the bodily responses that automatically deploy in trying to keep you warm! And vice-versa! Oo-er.

If you come out of the sea cold and have a hot shower in an attempt to warm up, your body goes, "It's hot out there" and pops out your veins etc. as its normal means of cooling in a warm environment. Meanwhile, your core is still freezin'.

If you drink ice cold fluid when hot but in the shade, your body can assume its generally cold, so it operates body responses for dealing with cold environments, perhaps reducing your sweating and drawing in your surface veins, so you can't cool as quickly.

The mechanism that you're describing is the opening and closing of the blood flow in the skin... the largest organ of the body. That has a massive effect on heat loss and is controlled by the brain through the autonomic nervous system in addition to local factors.

In addition to that there are several areas of the body that have specialised counter-current systems to regulate temperature. In (half of) humans this includes the rete mirabilis that stops the testes from overheating.

Jonathan

PS: The control of skin blood flow in mammals is mostly by the arterioles, just before the capillaries, rather than the veins. But it's the effect that matters for this discussion.

Sweep wrote: ↑11 Jul 2022, 10:24am ...
My skin seemed to develop small bumps - something to do with trying to shed more heat?

all returned to normal on getting under the trees and some water and cheap wine.

No itching or inflammation? How does this description of miliaria crystalline match up?
https://en.wikipedia.org/wiki/Miliaria

Jonathan

Vorpal wrote: ↑11 Jul 2022, 10:01am I have played football in 40 C, worked in agriculture in similar temperatures, and worked in the desert in the USA. I have not, that I am aware, suffered heat exhaustion, even though I don't really like the heat.

We were always told not to drink sugary drinks, like sports drinks, as this can make you lose more body fluid, but to drink water (not too cold) and add electrolyte drops or tablets to every third or fourth drink (the ones with salts in are best). They also said, at least 1/2 litre of water per hour, when exerting yourself. That's a rule of thumb, and an individual may need somewhat more. But as noted above, don't drink too much without replacing salts & electrolytes.

Bananas and potatoes (or sweet potatoes) are good snacks for the potassium, and slow release carbs. And, as others have said salt is important, too.

I've worked in 48 degrees c at >90% humidity and I can confirm that it is HORRIBLE. Could only really work in 20 minute bursts.

We were drinking upwards of 2 litres an hour and were adding the WHO recommended ratio of 8tsp of sugar/1tsp of salt per litre to aid hydration. Not Ideal, but all we had at the time. We did eventually get proper electrolyte tablets which really helped.

Jdsk wrote: ↑11 Jul 2022, 10:11am

Vorpal wrote: ↑11 Jul 2022, 10:01amWe were always told not to drink sugary drinks, like sports drinks, as this can make you lose more body fluid...

I don't know of a physiological mechanism that would do that. For most people the renal threshold for glucose is too high for osmotic diuresis to occur.

But the promotion of "sports drinks" is probably one of the major reasons that overhydration occurs. And, as above, that can cause serious problems.

Jonathan

There is some evidence that glucose in small quantities aids electrolyte and sodium absorption (hence the inclusion of it in sports drinks). But it can cause problems once you are dehydrated, and is especially problematic for those who work in high temperatures or are chronically dehydrated.

Experts believe that too much sugar may make dehydration and other symptoms worse. This is likely because of the interaction of sugar and water within the cells. Higher sugar intake causes the cells in the body to transfer more water and increase urination.

Lower levels of hydration in the body decrease the volume of the cells, which may impact a person’s blood sugar.

When a person has very high blood sugar, their body may borrow water from other areas to balance out the volume in the cells. This can influence cellular hydration. Higher blood sugar may also cause the body to urinate more to get rid of this excess sugar, which can influence dehydration. The extent of these effects and how long they last may vary.

https://www.medicalnewstoday.com/articl ... ary-drinks

Rehydration with soft drink-like beverages exacerbates dehydration and worsens dehydration-associated renal injury https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6195650/

Dehydration can affect glycogen regulation
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7551868/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6397405/

Vorpal wrote: ↑11 Jul 2022, 11:18am

Experts believe that too much sugar may make dehydration and other symptoms worse. This is likely because of the interaction of sugar and water within the cells. Higher sugar intake causes the cells in the body to transfer more water and increase urination.

Lower levels of hydration in the body decrease the volume of the cells, which may impact a person’s blood sugar.

When a person has very high blood sugar, their body may borrow water from other areas to balance out the volume in the cells. This can influence cellular hydration. Higher blood sugar may also cause the body to urinate more to get rid of this excess sugar, which can influence dehydration. The extent of these effects and how long they last may vary.

https://www.medicalnewstoday.com/articl ... ary-drinks

Rehydration with soft drink-like beverages exacerbates dehydration and worsens dehydration-associated renal injury https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6195650/

Dehydration can affect glycogen regulation
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7551868/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6397405/

Yes, there are many metabolic and compartmental effects, and we certainly don't know enough about the effects of fructose.

But I didn't see anything in those papers about sugary or sports drinks causing healthy people to lose more body fluid.

Jonathan

Jdsk wrote: ↑11 Jul 2022, 10:05am

Psamathe wrote: ↑10 Jul 2022, 11:26am From a non-medical perspective I think different people tolerate heat and it's effects differently. From my various travels I seem to handle heat a lot better than many others i.e. on quite a few occasions others really suffering whilst I'm only beginning to show maybe initial signs.

I don't know about individual physiological variations in tolerance... and once upon a time I was involved in deliberately heating people up to see what happened!

But the most important ways of increasing tolerance are behavioural, and those can be learnt. And of course there are particular risks when we *move into other environments where we don't know the tricks. Cycling in an unfamiliar environment is wide open to those, and having an external target to meet rather than resting in the shade with the locals can be the last straw,

Jonathan
...

(Again, from a non-medical personal observation perspective) I wonder if some of the individual variation is how different people react. On more than one occasion I suspect I've been into bad physiological reaction but I don't panic, just consider my options and decide on the best and do it. e.g. many years ago I decided I was going to go to see the Valley of the Kings (Egypt) independently, on foot (daft idea but I was young). I got a lift in a local boat across the Nile and walked. Walking through a local hamlet an air-con bus was stopped with one occupant on the ground (at least close to unconscious) from heat. I went round tombs and started walking back (getting hot now) and fairly quickly realised I'd stopped sweating - but in middle of desert, blazing Sun options are limited (stay where you are or carry on). Sorted myself out but at no point any panic or sense of doom - just consider options and take the best available.

Ian