Physiology of sweating

[Dangerscouse]

As I had quite a lot of time to think this morning, I was wondering about the process of sweating. When I drink during a long distance, will the body prioritise general rehydration over filling my bladder?

I have noticed that I don't need to drink as much as is always suggested, but I was also a bit concerned that if I drink too much I'll be desperate for the toilet. I think after eight years of hot dynamic Pilates (30c), and not drinking on any row less than 30k, I've built up a heat tolerance so dehydration doesn't effect me like it seems to with others.

I'm probably worrying too much about it, and I didn't have an issue today, but it got me wondering if there is a sweating hierarchy. I'm also probably asking a question that is far too esoteric and niche.

[KeithT]

As I had quite a lot of time to think this morning, I was wondering about the process of sweating. When I drink during a long distance, will the body prioritise general rehydration over filling my bladder?

I have noticed that I don't need to drink as much as is always suggested, but I was also a bit concerned that if I drink too much I'll be desperate for the toilet. I think after eight years of hot dynamic Pilates (30c), and not drinking on any row less than 30k, I've built up a heat tolerance so dehydration doesn't effect me like it seems to with others.

I'm probably worrying too much about it, and I didn't have an issue today, but it got me wondering if there is a sweating hierarchy. I'm also probably asking a question that is far too esoteric and niche.

So, I told you I recently read a book about recovery called "Good -to Go". The beginning of the book deals with hydration and very coincidentally the book has quotes from a cousin of mine who has PHDs and 19 years of testing about hydration for the Army (I didn't know he was in the book as I read it). Anyway, the science/evidence shows people are rarely dehydrated and there have been more issue with people being over-hydrated in Marathons and such than under. Basically, the human body does an amazing job of keeping you hydrated and tells you (thirst) when you need to drink. That said you prob still want to be "adequately hydrated" but nothing extreme which bodes well if you don't want to use the restroom.

[Dangerscouse]

So, I told you I recently read a book about recovery called "Good -to Go". The beginning of the book deals with hydration and very coincidentally the book has quotes from a cousin of mine who has PHDs and 19 years of testing about hydration for the Army (I didn't know he was in the book as I read it). Anyway, the science/evidence shows people are rarely dehydrated and there have been more issue with people being over-hydrated in Marathons and such than under. Basically, the human body does an amazing job of keeping you hydrated and tells you (thirst) when you need to drink. That said you prob still want to be "adequately hydrated" but nothing extreme which bodes well if you don't want to use the restroom.

Thanks Keith. I have heard about over hydration, but it is good to hear it's probably not an issue. I regularly lose a few kilograms when I do long distances, but I do put it all back on again fairly quickly. I think I lost about 13 kilos when I did my 12hr challenge, so it's probably nothing to worry about, as I didn't have any notable issues then.

[ArmandoChavezUNC]

So, I told you I recently read a book about recovery called "Good -to Go". The beginning of the book deals with hydration and very coincidentally the book has quotes from a cousin of mine who has PHDs and 19 years of testing about hydration for the Army (I didn't know he was in the book as I read it). Anyway, the science/evidence shows people are rarely dehydrated and there have been more issue with people being over-hydrated in Marathons and such than under. Basically, the human body does an amazing job of keeping you hydrated and tells you (thirst) when you need to drink. That said you prob still want to be "adequately hydrated" but nothing extreme which bodes well if you don't want to use the restroom.

Your cousin is a very smart man and what you referenced is exactly why the multi-billion dollar energy/electrolyte drink business is a total sham and people just waste their money with these products. But they have funded so much "research" through the likes of the Gatorade lab and their advertisements are so ubiquitous that everybody falls for it.

[MiddleAgeCRISIS]

The only thing i would add is - it is vital not to have an extended period of dehydration especially when combined with rapid weight loss.

My understanding is that the secretions of ketones takes priority over urea.Failing to secrete urea can lead to gout.

This happened to me when i decided to row 20km per day for a month followed by 2 weeks riding 40 miles per day in a heat wave.

It took me 4 years to sort the gout issue out.

[Nomath]

Just put yourself on a scale before and after an exercise (and before you go for a pee). My experience : I lose 0.3 kg on a 5K row (20-23 min), independent of my pace. I lose 0.6 kg on a 10K row (41-45 min).
If you account for the work done and the mechanical efficiency of a human body, you will find that about half of the weight loss is due to burning fuel stocks and the other half is from sweating, direct evaporation from the skin to cool the body and from moistening breathed air. Nobody gets dehydrated from exercising less than 60 mins.

[Tandstad]

Interesting topid this! I sweat more than most(hyperhidrosis and overweight) but I still see no big change in performance on "long" rows, long for me that is. I have done up to 90 min sessions with negative splits, and I am not dying for a drink after. I just ensure I drink sufficient early the same day, and I am good to go.

I think I felt it more when I was running competitions(at a very low level) in 25 degrees C going up a mountain. Many people say you can lose 30% in your performance if you do not stay hydrated, so it is interesting indeed. If these numbers are evidence based I do not know.

[Nomath]

I'm probably worrying too much about it, and I didn't have an issue today, but it got me wondering if there is a sweating hierarchy. I'm also probably asking a question that is far too esoteric and niche.

Your question is far from esoteric, as it haunts many endurance athletes, especially those exercising in a hot and dry environment.
Nowadays, textbooks on physiology are haphazardly freely available on the internet. See if you can download a copy of Jay Hoffman's Physiological Aspects of Sport Training and Performance.
My edition (2002) has a Chapter 16 dealing with Hydration. I have seen graphs (figure 16.6) comparing Avid drinkers and Reluctant drinkers. Maybe you find something to calm down your worries.

[Dangerscouse]

Your question is far from esoteric, as it haunts many endurance athletes, especially those exercising in a hot and dry environment.
Nowadays, textbooks on physiology are haphazardly freely available on the internet. See if you can download a copy of Jay Hoffman's Physiological Aspects of Sport Training and Performance.
My edition (2002) has a Chapter 16 dealing with Hydration. I have seen graphs (figure 16.6) comparing Avid drinkers and Reluctant drinkers. Maybe you find something to calm down your worries.

Thanks, this looks ideal

[iain]

I lose 1kg or so on a 90min row (more in hot conditions), but IIRC it is only >2% loss that is an issue. The greater issue I have found is that trying to take in food on a long row is very difficult, it is easier to take in calories in drinks. This is the main reason that I drink a lot on FM or longer. Too concentrated and I get stomach cramps.

[KeithT]

So, I told you I recently read a book about recovery called "Good -to Go". The beginning of the book deals with hydration and very coincidentally the book has quotes from a cousin of mine who has PHDs and 19 years of testing about hydration for the Army (I didn't know he was in the book as I read it). Anyway, the science/evidence shows people are rarely dehydrated and there have been more issue with people being over-hydrated in Marathons and such than under. Basically, the human body does an amazing job of keeping you hydrated and tells you (thirst) when you need to drink. That said you prob still want to be "adequately hydrated" but nothing extreme which bodes well if you don't want to use the restroom.

Your cousin is a very smart man and what you referenced is exactly why the multi-billion dollar energy/electrolyte drink business is a total sham and people just waste their money with these products. But they have funded so much "research" through the likes of the Gatorade lab and their advertisements are so ubiquitous that everybody falls for it.

Yes, that is exactly what he says. The science behind the claimed results is really bad too.

[Cyclist2]

I agree that consuming large amounts of electrolyte drink is probably more marketing than science but replacing those micro nutrients is definitely important. My personal experience with it during my early cycling training convinced me. I was really ramping up my miles and efforts - I'd get home on the verge of "bonking" almost every ride, taking a couple hours to recover. I noticed after a while that I just wasn't feeling "right" even with no riding. I started taking a daily multivitamin and that symptom disappeared. I was sweating out too much of those trace elements without replacing them and my body was just "off".

So, yeah, I take water and an electrolyte drink with me on long rides or rows, but sure don't swear by it, just makes me more comfortable. Daily multivitamin always.

[jamesg]

At a guess, the more we sweat, the more we'll have to take in water and with it the lost Na and K. Lack of certainly shows, unlikely or not.

[jurgwhitehouse]

'Waterlogged: The Serious Problem of Overhydration in Endurance Sports' by Tim Noakes is good. Since reading it I now only drink when I feel thirsty.

[GlennUk]

I've been looking at rehydration and have trouble consuming the amounts of water 'recommended' when considering drinking by programme.

Drinking to thirst makes a loft of sense to me, I plan to have water/electrolyte mix available thorgh out all of my longer ergs in abundance. Mostly I have erged/exercised without following any particular regime for drinking but that has been for durations of up to c.90 minutes or so.

My first longer duraiont will last 4-5 hours so be interesting to see how i feel during/after that and understand how much fluid i take on.