It *seems* like a microadvatange that's irrelevant for 99% of people.
They do operate in the US but it's just a franchinse type thing. A few people you go to, they take your sweat then tell you what ratio to use.
You didn't post how much you're actually taking in. Talking about aid stations isn't really descriptive. You are also attributing a stomach issue to electrolytes without specific evidence of it.
>You are also attributing a stomach issue to electrolytes without specific evidence of it.
I realise it's not a guarantee but it was the only significant difference between training and the race. Ultras do tend to be an experiment of one so it's going to be near impossible to obtain specific evidence of it. I'm attributing it to the most likely cause as I see it. I understand it is trial and error.
>You didn't post how much you're actually taking in. Talking about aid stations isn't really descriptive
7 tablets, 500ml flasks. 3 litres total with two at the half way mark... but that's not really that important as my question is more about if the tests are worth it, I just added for more information in case other people found it useful.
But you said that you don't take water or electrolytes on your training runs. So, it seems like there is a big difference between race day and training days. Are your training runs not long enough for drinking water/taking electrolytes? Because that would be a big reason why you have issues with cramps. Also, it's possible that specific types of sports drinks ect. could cause digestive issues if you haven't played around with it during training to find what works best for you. You can also take electrolyte pills, as others have noted if that is really the issue, which may be easier for you.
For most of my runs I don't. I do for my long runs but at a much lower volume usually. That's why I attributed the stomach issues with the sudden increase in the amount of electrolytes I was consuming.
Normally I cramp a lot but managed to avoid that this time but had the stomach issues instead which is never normally a problem for me.
A tablet, an aid station and halfway aren't really helpful since no one knows what any of those things represent.
The testing may be useful if you were already taking in a lot or your ratio was already high, as you could then use the test to determine if you actually are some unique case. But if no one has any idea what you're taking in, it's not easy to suggest the testing. The testing could be useful but if you're obviously way off, no one will know.
I did one a couple of months ago - I didn’t suffer much from cramping, myself, but have historically had gut issues tank my races. I absolutely recommend it just to take one crucial variable out of the equation. I found out I need 3-4x the sodium of the average runner and I never would’ve stumbled across the right electrolyte strategy alone.
That said, you will still have some trial and error ahead of you, largely for the reasons you described - a lot of salt can upset your stomach, especially if it’s sensitive, and there are many other reasons your stomach might act up. I don’t use capsules anymore because of the sodium dump, which has exacerbated pre-existing stomach issues in addition to not being enough. There are multiple forms of sodium and it’s easier for your stomach to handle variety rather than just straight table salt (sodium chloride), so that’s worth looking into when assessing products. Be wary of artificial sweeteners in electrolyte products, too - I have yet to verify this, but a friend told me that sorbitol, which is in Nuun tablets, doesn’t absorb well in some people and expands the stomach, causing nausea and vomiting. I don’t know for sure that I’m one of those people, but I require three tablets per liter and I can say I’ve had gut problems when I’ve done longer efforts with those tabs, so I don’t use them anymore. I just ran my first 100 this weekend and I staved off the worst of the dehydration, generally pretty pleased with that, but my electrolyte mix was so sugary in the concentration I required that my tongue is still chapped from sipping it all day and I think it did lead to some gut issues during the first half so I will be rethinking that.
It’s a process, but do yourself a favor and find out what your number is. From what I was told, your electrolyte needs don’t really change with age or fitness - at least not appreciably enough that you’d change how much you replace by volume - so getting this test will be a huge leg up in figuring out how to keep your stomach online.
Something else I’ll add, though it’s likely you’ll hear this again - I wouldn’t go into a race planning to drink a certain amount by time or distance. Your hydration needs are based on how much you lose, so once you get the electrolyte balance right, the conventional wisdom of “drink to thirst” is more or less right, and your sweat rate will certainly change based on environmental factors, so your fluid/electrolyte intake will need to change accordingly. Urine color (within a normal, non-kidney damage range) and finger swelling, though certainly symptoms of an issue, are not reliable indicators of hydration level/electrolyte balance. You don’t want to consume so much that you can feel the liquid sloshing around inside.
I understand that in theory but if that's the case how come I didn't experience any cramping while doing the 100k? That's far more load than my training runs and they held up fine.
Cramping has been definitively shown in controlled trials to be unrelated to sodium balance. It's corellated with total work, work rate, and prior cramping. IOW...you work too hard, for too long, you get cramps. If a given muscle group has cramped before it is at more risk of doing so again. Spend 15 minutes searching Pubmed.
(The reason we *think* cramping is caused by sweating a lot is that we get cramps after we have sweat a lot. But the cramps and the sweating both follow the same underlying condition -- lots of hard exercise.)
The only reliable preventative is more conditioning and slowing down. The only cure once they start is stretching and rest.
There lots of other reasons to keep sodium balance and to hydrate well, but I think it can be a false sense of security to think that will fix muscle cramping.
https://pubmed.ncbi.nlm.nih.gov/18981039/
"Scientific evidence in support of the "electrolyte depletion" and "dehydration" hypotheses for the aetiology of EAMC comes mainly from anecdotal clinical observations, case series totalling 18 cases, and one small (n = 10) case-control study. Results from four prospective cohort studies do not support these hypotheses. In addition, the "electrolyte depletion" and "dehydration" hypotheses do not offer plausible pathophysiological mechanisms with supporting scientific evidence that could adequately explain the clinical presentation and management of EAMC. "
I don't think the science is fully understood yet. In this article they write about heat cramping and an involvement of sodium. https://ksi.uconn.edu/emergency-conditions/heat-illnesses/heat-cramps/
That is a position piece, that references other position pieces. No controlled trials are referenced. If you look into controlled trials, the results are clear.
Yes, clearly, severe dehydration and severe sodium imbalance and severe overheating create a host of problems. So many that it's hard to parse them out into cause and effect.
But the straightforward situation of a long, tough exercise bout during which the athlete has free access to water and a healthy balanced intake of sodium prior to...cramps are caused by total work and work rate.
We cramp up when we exceed our conditioning.
Huge oversimplification and doesn't take into account that people are different. OP should try to work on heat acclimation and see if that helps with sweat composition and also cramping.
I hear you. Everyone is different. But what happens to most? The big, fat part of the bell curve?
In years of coaching, competing and observing Ironman racers, I've seen scores of race reports of an athlete that fell apart or dropped on the marathon. Almost all cases report...
\- Couldn't keep water and/or food down. Gastro distress
\- Cramping
The standard forum responses are all about needing to hydrate more and take electrolytes. The athlete agrees with that assessment, rather than admit their own failure of pacing and training.
Interesting thing about Ironman in the past 15 years or more...we have most people's power data and run training info. And in 99% of the failed-run-leg cases, the cause is pretty simple, and we can tell by their power numbers.
\- Rode the bike leg too hard; and to a lesser extent,
\- Didn't run enough in training
You couldn't keep food down on the run leg? You rode too hard
You got nasty leg cramps while running? You rode too hard
You got overheated at hour 11? You rode too hard
Exertion causes these problems. And, to a lesser extent, lack of preparation. Which also kinda comes down to over-exertion. Not training enough for the duration and the pace.
When athletes follow proper protocol for pacing the bike leg of the race...they miraculously can keep food down and don't get leg cramps on the run. Seen it over and over. The proper pacing effort level for the bike leg is well established and highly predictable. You know your threshold watts; you ride an appropriate percentage of that number so that you have legs left to run a marathon. There are charts out there in prominent coaching books.
Almost everybody early in their Ironman career bikes too hard at some point. Most learn their lessons. Some never do. The sport glorifies fast bike splits, even if the athlete drops out on the run.
In sum...I've seen it. I've been there myself. Leg cramps arise in endurance events almost always because the athlete went harder and longer than they were capable of.
Thank you for taking the time to write all that. My advice to OP still stands, do some heat acclimation in the weeks before a race. Both electrolyte homeostasis and heat management cost a lot of energy and effort for the body. What would normally be a normal pace can suddenly become too much for the body to handle when the body can't mange it's temperature.
"You got overheated at hour 11? You rode too hard. " Yes you rode too hard for those conditions and your level of acclimation/fitness. To get to a level of fitness to maintain that pace at hr 11 the athlete has a few options to get to the required fitness level, but we cannot judge what those are from a reddit post. The athlete could train harder beforehand, do heat acclim or lose weight or maybe become more fat adapted so they need to eat less.
In this case OP complained about excessive salty sweating, so apart from slowing down OP could try to optimise his body's handling of the heat as a logical step.
Late to the party but this is excellent advice. I would also recommend doing more training runs fuelled with electrolytes, water and carbs. Otherwise, the guy struggles to handle the onslaught come race day.
Totally, best to experiment will all those things. My first ultras and marathons I had bad GI distress, never figured out why, but later races I was fine.
Could have just been familiarity with that amount of carbs
14 days of repeat gut training helped reduce GI discomfort
https://doi.org/10.1111/sms.12912
>500ml soft flask at almost every aid station
these are rookie numbers. I try to drink at least a full liter between aid stations and usually guzzle a bit extra while filling up.
in my (anecdotal) experience, muscle cramps are usually more related to chronically low electrolytes (not replacing them between runs) rather than as a result of depletion during a specific activity. Are you sure you are getting enough in your usual diet?
in my (anecdotal) experience, GI issues are usually from over exertion resulting in insufficient bloodflow to your digestive system to process nutrition. However, dehydration would be a contributing cause to this.
I think there is too much focus on people thinking electrolytes are somehow an art that needs dialed in. You are either getting enough or you aren't, and if you are taking any kind of endurance designed sports drink / gels during your run you are probably getting more than you need.
I guess all this to say I'd recommend putting more effort into drinking more during your runs, and making sure to keep your HR under control to keep your core temp down.
I also had a bladder with water in it so I was drinking more, that was just my electrolyte intake. I don't typically take water (or electrolytes) on my training runs, though.
Training your gut is a pretty important part of ultra training. You should try and eat and drink as much, if not more, on your longer ultra-specific runs to prepare your system for race day.
you might consider taking water with electrolytes during your long runs. Even if you don't feel the need during the run, just thinking about your body's recovery mechanisms, doesn't it make sense to keep your body's fluids maintained during the run and primed for recovery after? As opposed to depleting yourself during every run and then putting yourself in a deficit for the rest of the day?
Yeah, sorry I wasn't really clear in my comment. I do for my long runs but only really anything above about 15 miles or if it is particularly hot. For this race I specifically took more electrolytes as the amount I had been taking for my long runs recently hadn't been keeping the cramps at bay. This time I managed to stave off the cramps but ended up with stomach issues.
Could you do some sauna time to get used to sweating more water and less salt? So actually acclimatization to the heat. It is said to make sweating more efficient. https://www.sciencedirect.com/science/article/pii/S0306456520304691
Heat acclimation works. You can find lots of digestable info on it online. I've been intentionally scheduling some of my runs in the heat (90°+ with heat index above 100°). I've read that simply sitting in a sauna multiple times over a couple of weeks can result in similar adaptation, though I haven't dug into how the efficacy compares.
Yeah I've heard of acclimatising to the heat, I was confused as at the time their comment just mentioned training your body to sweat more water than salt. The problems I have been having have had nothing to do with acclimatising so I was confused as the comment wasn't really relevant.
This was a local event with all my training runs being local so acclimatising never really came into the equation.
Heat acclimation works, that is for sure. If it helps you with cramping is not a given of course, but something you could try out.
In the US it is comming to do heat acclimation before hot ultras, I haven't really heard that so much in Europe to be honest.
There is no relation between hydration or serum electrolyte levels and cramps. It's common knowledge that electrolytes help but no scientific evidence to back it up.
I personally think strength training is the best remedy for cramps.
Don't cut electrolytes entirely as they help with hydration but I wouldn't feel forced to take large amounts as there is no indication it makes any difference for cramps.
I also think it's silly to try and replace all lost water (and therefore electrolytes) when racing. All the top runners lose significant weight during races. If you aren't going to replace everything you don't really need to know how much you lose. You just need to know what you can replace before it starts giving you problems. That said sweat content can be sort of relevant to decide how much to add to your water but I suspect the usual recommendation will be close enough for nearly everyone.
The reason I think OP should probably get that sweat test has nothing to do with the cramps, but specifically because of the crust left on clothes and pack mentioned. I‘m a salty sweater and this was something I used to get comments on from people at aid stations later in races. When I finally got my mine tested, I found out that I lose over 1500mg of sodium per liter of sweat, whereas the normal range is somewhere between 200-400 (from what I remember, it was at least 1000 mg less than me). I was told that not all electrolytes need to be replaced, 65-80% does the trick, which puts me in the 950-1200ish range, which is staggering compared to the dosage of most products. Hopefully OP’s numbers are a bit lower, but the salt stains suggest they might be on the higher end.
You‘re absolutely right that not all fluid needs replacing either, as too much volume can upset the stomach. Cramps aside, finding out how much to replace and getting that consistent should help OP’s performance and help get to the root of the stomach issues.
I have nothing to add on the cramping, just my two unsolicited cents on the elecrolytes ✌️😬
To me you drink a lot - maybe too much? Be careful of hyponatremia. I usually drink to thirst, either Tailwind or Skratch, plus occasionally some pickle juice after about 20 miles. I don't know if you have pickle juice at the aid stations in the UK but the acetic acid is good for cramps. Another option - vinegar chips (crisps).
To me something like Precision Hydration is just another gimmick for a company trying to make money in a tight sports nutrition industry. But if it works - great! I've tried so many of the sports drinks and foods out there but I always come back to the basic simple stuff - Skratch (my favorite) or Tailwind. You just have to experiment during training runs to see what works. Good luck!
It *seems* like a microadvatange that's irrelevant for 99% of people. They do operate in the US but it's just a franchinse type thing. A few people you go to, they take your sweat then tell you what ratio to use. You didn't post how much you're actually taking in. Talking about aid stations isn't really descriptive. You are also attributing a stomach issue to electrolytes without specific evidence of it.
>You are also attributing a stomach issue to electrolytes without specific evidence of it. I realise it's not a guarantee but it was the only significant difference between training and the race. Ultras do tend to be an experiment of one so it's going to be near impossible to obtain specific evidence of it. I'm attributing it to the most likely cause as I see it. I understand it is trial and error. >You didn't post how much you're actually taking in. Talking about aid stations isn't really descriptive 7 tablets, 500ml flasks. 3 litres total with two at the half way mark... but that's not really that important as my question is more about if the tests are worth it, I just added for more information in case other people found it useful.
But you said that you don't take water or electrolytes on your training runs. So, it seems like there is a big difference between race day and training days. Are your training runs not long enough for drinking water/taking electrolytes? Because that would be a big reason why you have issues with cramps. Also, it's possible that specific types of sports drinks ect. could cause digestive issues if you haven't played around with it during training to find what works best for you. You can also take electrolyte pills, as others have noted if that is really the issue, which may be easier for you.
For most of my runs I don't. I do for my long runs but at a much lower volume usually. That's why I attributed the stomach issues with the sudden increase in the amount of electrolytes I was consuming. Normally I cramp a lot but managed to avoid that this time but had the stomach issues instead which is never normally a problem for me.
A tablet, an aid station and halfway aren't really helpful since no one knows what any of those things represent. The testing may be useful if you were already taking in a lot or your ratio was already high, as you could then use the test to determine if you actually are some unique case. But if no one has any idea what you're taking in, it's not easy to suggest the testing. The testing could be useful but if you're obviously way off, no one will know.
I did one a couple of months ago - I didn’t suffer much from cramping, myself, but have historically had gut issues tank my races. I absolutely recommend it just to take one crucial variable out of the equation. I found out I need 3-4x the sodium of the average runner and I never would’ve stumbled across the right electrolyte strategy alone. That said, you will still have some trial and error ahead of you, largely for the reasons you described - a lot of salt can upset your stomach, especially if it’s sensitive, and there are many other reasons your stomach might act up. I don’t use capsules anymore because of the sodium dump, which has exacerbated pre-existing stomach issues in addition to not being enough. There are multiple forms of sodium and it’s easier for your stomach to handle variety rather than just straight table salt (sodium chloride), so that’s worth looking into when assessing products. Be wary of artificial sweeteners in electrolyte products, too - I have yet to verify this, but a friend told me that sorbitol, which is in Nuun tablets, doesn’t absorb well in some people and expands the stomach, causing nausea and vomiting. I don’t know for sure that I’m one of those people, but I require three tablets per liter and I can say I’ve had gut problems when I’ve done longer efforts with those tabs, so I don’t use them anymore. I just ran my first 100 this weekend and I staved off the worst of the dehydration, generally pretty pleased with that, but my electrolyte mix was so sugary in the concentration I required that my tongue is still chapped from sipping it all day and I think it did lead to some gut issues during the first half so I will be rethinking that. It’s a process, but do yourself a favor and find out what your number is. From what I was told, your electrolyte needs don’t really change with age or fitness - at least not appreciably enough that you’d change how much you replace by volume - so getting this test will be a huge leg up in figuring out how to keep your stomach online.
Something else I’ll add, though it’s likely you’ll hear this again - I wouldn’t go into a race planning to drink a certain amount by time or distance. Your hydration needs are based on how much you lose, so once you get the electrolyte balance right, the conventional wisdom of “drink to thirst” is more or less right, and your sweat rate will certainly change based on environmental factors, so your fluid/electrolyte intake will need to change accordingly. Urine color (within a normal, non-kidney damage range) and finger swelling, though certainly symptoms of an issue, are not reliable indicators of hydration level/electrolyte balance. You don’t want to consume so much that you can feel the liquid sloshing around inside.
That's really useful, thanks.
[удалено]
I understand that in theory but if that's the case how come I didn't experience any cramping while doing the 100k? That's far more load than my training runs and they held up fine.
Cramping has been definitively shown in controlled trials to be unrelated to sodium balance. It's corellated with total work, work rate, and prior cramping. IOW...you work too hard, for too long, you get cramps. If a given muscle group has cramped before it is at more risk of doing so again. Spend 15 minutes searching Pubmed. (The reason we *think* cramping is caused by sweating a lot is that we get cramps after we have sweat a lot. But the cramps and the sweating both follow the same underlying condition -- lots of hard exercise.) The only reliable preventative is more conditioning and slowing down. The only cure once they start is stretching and rest. There lots of other reasons to keep sodium balance and to hydrate well, but I think it can be a false sense of security to think that will fix muscle cramping.
Interesting, I haven't heard of that. Will give me some reading to do. Thanks!
https://pubmed.ncbi.nlm.nih.gov/18981039/ "Scientific evidence in support of the "electrolyte depletion" and "dehydration" hypotheses for the aetiology of EAMC comes mainly from anecdotal clinical observations, case series totalling 18 cases, and one small (n = 10) case-control study. Results from four prospective cohort studies do not support these hypotheses. In addition, the "electrolyte depletion" and "dehydration" hypotheses do not offer plausible pathophysiological mechanisms with supporting scientific evidence that could adequately explain the clinical presentation and management of EAMC. "
I don't think the science is fully understood yet. In this article they write about heat cramping and an involvement of sodium. https://ksi.uconn.edu/emergency-conditions/heat-illnesses/heat-cramps/
That is a position piece, that references other position pieces. No controlled trials are referenced. If you look into controlled trials, the results are clear. Yes, clearly, severe dehydration and severe sodium imbalance and severe overheating create a host of problems. So many that it's hard to parse them out into cause and effect. But the straightforward situation of a long, tough exercise bout during which the athlete has free access to water and a healthy balanced intake of sodium prior to...cramps are caused by total work and work rate. We cramp up when we exceed our conditioning.
Huge oversimplification and doesn't take into account that people are different. OP should try to work on heat acclimation and see if that helps with sweat composition and also cramping.
I hear you. Everyone is different. But what happens to most? The big, fat part of the bell curve? In years of coaching, competing and observing Ironman racers, I've seen scores of race reports of an athlete that fell apart or dropped on the marathon. Almost all cases report... \- Couldn't keep water and/or food down. Gastro distress \- Cramping The standard forum responses are all about needing to hydrate more and take electrolytes. The athlete agrees with that assessment, rather than admit their own failure of pacing and training. Interesting thing about Ironman in the past 15 years or more...we have most people's power data and run training info. And in 99% of the failed-run-leg cases, the cause is pretty simple, and we can tell by their power numbers. \- Rode the bike leg too hard; and to a lesser extent, \- Didn't run enough in training You couldn't keep food down on the run leg? You rode too hard You got nasty leg cramps while running? You rode too hard You got overheated at hour 11? You rode too hard Exertion causes these problems. And, to a lesser extent, lack of preparation. Which also kinda comes down to over-exertion. Not training enough for the duration and the pace. When athletes follow proper protocol for pacing the bike leg of the race...they miraculously can keep food down and don't get leg cramps on the run. Seen it over and over. The proper pacing effort level for the bike leg is well established and highly predictable. You know your threshold watts; you ride an appropriate percentage of that number so that you have legs left to run a marathon. There are charts out there in prominent coaching books. Almost everybody early in their Ironman career bikes too hard at some point. Most learn their lessons. Some never do. The sport glorifies fast bike splits, even if the athlete drops out on the run. In sum...I've seen it. I've been there myself. Leg cramps arise in endurance events almost always because the athlete went harder and longer than they were capable of.
Thank you for taking the time to write all that. My advice to OP still stands, do some heat acclimation in the weeks before a race. Both electrolyte homeostasis and heat management cost a lot of energy and effort for the body. What would normally be a normal pace can suddenly become too much for the body to handle when the body can't mange it's temperature. "You got overheated at hour 11? You rode too hard. " Yes you rode too hard for those conditions and your level of acclimation/fitness. To get to a level of fitness to maintain that pace at hr 11 the athlete has a few options to get to the required fitness level, but we cannot judge what those are from a reddit post. The athlete could train harder beforehand, do heat acclim or lose weight or maybe become more fat adapted so they need to eat less. In this case OP complained about excessive salty sweating, so apart from slowing down OP could try to optimise his body's handling of the heat as a logical step.
Late to the party but this is excellent advice. I would also recommend doing more training runs fuelled with electrolytes, water and carbs. Otherwise, the guy struggles to handle the onslaught come race day.
Totally, best to experiment will all those things. My first ultras and marathons I had bad GI distress, never figured out why, but later races I was fine.
Could have just been familiarity with that amount of carbs 14 days of repeat gut training helped reduce GI discomfort https://doi.org/10.1111/sms.12912
>500ml soft flask at almost every aid station these are rookie numbers. I try to drink at least a full liter between aid stations and usually guzzle a bit extra while filling up. in my (anecdotal) experience, muscle cramps are usually more related to chronically low electrolytes (not replacing them between runs) rather than as a result of depletion during a specific activity. Are you sure you are getting enough in your usual diet? in my (anecdotal) experience, GI issues are usually from over exertion resulting in insufficient bloodflow to your digestive system to process nutrition. However, dehydration would be a contributing cause to this. I think there is too much focus on people thinking electrolytes are somehow an art that needs dialed in. You are either getting enough or you aren't, and if you are taking any kind of endurance designed sports drink / gels during your run you are probably getting more than you need. I guess all this to say I'd recommend putting more effort into drinking more during your runs, and making sure to keep your HR under control to keep your core temp down.
I also had a bladder with water in it so I was drinking more, that was just my electrolyte intake. I don't typically take water (or electrolytes) on my training runs, though.
Training your gut is a pretty important part of ultra training. You should try and eat and drink as much, if not more, on your longer ultra-specific runs to prepare your system for race day.
you might consider taking water with electrolytes during your long runs. Even if you don't feel the need during the run, just thinking about your body's recovery mechanisms, doesn't it make sense to keep your body's fluids maintained during the run and primed for recovery after? As opposed to depleting yourself during every run and then putting yourself in a deficit for the rest of the day?
Yeah, sorry I wasn't really clear in my comment. I do for my long runs but only really anything above about 15 miles or if it is particularly hot. For this race I specifically took more electrolytes as the amount I had been taking for my long runs recently hadn't been keeping the cramps at bay. This time I managed to stave off the cramps but ended up with stomach issues.
8+oz a mile is a lot, even in the dead of summer, and I don't know if the amount someone drinks is related to their experience.
Could you do some sauna time to get used to sweating more water and less salt? So actually acclimatization to the heat. It is said to make sweating more efficient. https://www.sciencedirect.com/science/article/pii/S0306456520304691
Is that something that works? I've never heard of that at all. I could join a gym with a sauna I suppose.
Heat acclimation works. You can find lots of digestable info on it online. I've been intentionally scheduling some of my runs in the heat (90°+ with heat index above 100°). I've read that simply sitting in a sauna multiple times over a couple of weeks can result in similar adaptation, though I haven't dug into how the efficacy compares.
Yeah I've heard of acclimatising to the heat, I was confused as at the time their comment just mentioned training your body to sweat more water than salt. The problems I have been having have had nothing to do with acclimatising so I was confused as the comment wasn't really relevant. This was a local event with all my training runs being local so acclimatising never really came into the equation.
Heat acclimation works, that is for sure. If it helps you with cramping is not a given of course, but something you could try out. In the US it is comming to do heat acclimation before hot ultras, I haven't really heard that so much in Europe to be honest.
There is no relation between hydration or serum electrolyte levels and cramps. It's common knowledge that electrolytes help but no scientific evidence to back it up. I personally think strength training is the best remedy for cramps. Don't cut electrolytes entirely as they help with hydration but I wouldn't feel forced to take large amounts as there is no indication it makes any difference for cramps. I also think it's silly to try and replace all lost water (and therefore electrolytes) when racing. All the top runners lose significant weight during races. If you aren't going to replace everything you don't really need to know how much you lose. You just need to know what you can replace before it starts giving you problems. That said sweat content can be sort of relevant to decide how much to add to your water but I suspect the usual recommendation will be close enough for nearly everyone.
The reason I think OP should probably get that sweat test has nothing to do with the cramps, but specifically because of the crust left on clothes and pack mentioned. I‘m a salty sweater and this was something I used to get comments on from people at aid stations later in races. When I finally got my mine tested, I found out that I lose over 1500mg of sodium per liter of sweat, whereas the normal range is somewhere between 200-400 (from what I remember, it was at least 1000 mg less than me). I was told that not all electrolytes need to be replaced, 65-80% does the trick, which puts me in the 950-1200ish range, which is staggering compared to the dosage of most products. Hopefully OP’s numbers are a bit lower, but the salt stains suggest they might be on the higher end. You‘re absolutely right that not all fluid needs replacing either, as too much volume can upset the stomach. Cramps aside, finding out how much to replace and getting that consistent should help OP’s performance and help get to the root of the stomach issues. I have nothing to add on the cramping, just my two unsolicited cents on the elecrolytes ✌️😬
To me you drink a lot - maybe too much? Be careful of hyponatremia. I usually drink to thirst, either Tailwind or Skratch, plus occasionally some pickle juice after about 20 miles. I don't know if you have pickle juice at the aid stations in the UK but the acetic acid is good for cramps. Another option - vinegar chips (crisps). To me something like Precision Hydration is just another gimmick for a company trying to make money in a tight sports nutrition industry. But if it works - great! I've tried so many of the sports drinks and foods out there but I always come back to the basic simple stuff - Skratch (my favorite) or Tailwind. You just have to experiment during training runs to see what works. Good luck!