Post work weight loss doesn't equal fluid loss...?

[Joe Dwarf]

But even if there's a deficit, it will be less than a pound's worth of "real" weight from metabolism of fat and glucose.

Still, MOST of the weight you lose is water

Isn't that what I just said?

[Jwolf]

But even if there's a deficit, it will be less than a pound's worth of "real" weight from metabolism of fat and glucose.

Still, MOST of the weight you lose is water

Isn't that what I just said?

Yes- I agree with you and not Pat on this one. I just quoted both to continue the conversation...

(and the part of my answer you cut out was to answer La, so I was just being lazy in the quoting...)

[Pat Menzies]

The point is that your body requires about three pounds of water to hold one pound of glycogen in the body. That's very much temporary weight that isn't going to be reflected as dehydration when you lose it.
We don't actually require being puffed up with carbs and water to function perfectly normally.

[Jwolf]

The point is that your body requires about three pounds of water to hold one pound of glycogen in the body. That's very much temporary weight that isn't going to be reflected as dehydration when you lose it.

I don't understand-- It is "dehydration" as it's water lost. The body's water balance is all these things-- water lost from metabolism, sweating, glycogen storage, etc. La asked, "What is that weight I've lost if it's not water?" It is still mostly water. The carbon from the energy sources burned is still a small percentage of the weight lost.

I think that's really the point the article was making. You don't HAVE to replace all the water you lose through drinking (and you can't), so you will lose weight. You gain it back very quickly as you rehydrate over the course of the day. But didn't we already know this?

Isn't the main reason dehydration affects performance is that eventually your blood volume decreases? Your heart has to work harder to pump the blood around when there is less of it. But your blood volume won't decrease significantly until your fluid loss drops lower than a certain percentage of your body weight.

[La]

If I am understanding this correctly, the body mass lost (i.e., difference between pre- and post-workout weight) IS mostly water, however it doesn't necessarily mean that you have "dehydrated" yourself in the way that we normally use that term.

And the other thing I think the author is saying (though not very clearly) is that the "rule of thumb" we all used to determine how much water we lost during training doesn't necessarily apply. I have heard in the past (as Michael indicated) that it's not necessarily a bad thing to finish a race in a dehydrated state. The key is in making sure that you don't reach that state too early in your race, or that you don't dehydrate yourself to dangerous levels.

[Pat Menzies]

I would say it's not true dehydration becsuse the ability to store excess glycogen is a training response. The water stored in the body to hold glycogen is overhydration. It's just a step below glycerol loading.
You can hold even more water in your system that way.

[Jwolf]

If I am understanding this correctly, the body mass lost (i.e., difference between pre- and post-workout weight) IS mostly water, however it doesn't necessarily mean that you have "dehydrated" yourself in the way that we normally use that term.

And the other thing I think the author is saying (though not very clearly) is that the "rule of thumb" we all used to determine how much water we lost during training doesn't necessarily apply. I have heard in the past (as Michael indicated) that it's not necessarily a bad thing to finish a race in a dehydrated state. The key is in making sure that you don't reach that state too early in your race, or that you don't dehydrate yourself to dangerous levels.

Yes, but I also think that this article isn't telling us anything we didn't already know, is it? The measurements/calculations some people have used in the past have never recommended to try to replace ALL the water lost. I guess not worrying about a specific percentage of weight lost is the take-home message. Because each person's excess fluid volume will be different.

I would say it's not true dehydration because the ability to store excess glycogen is a training response. The water stored in the body to hold glycogen is overhydration. It's just a step below glycerol loading.
You can hold even more water in your system that way.

It's not "dehydration" in the sense of water lost from the blood, no. And you won't notice your urine getting darker because of it. It's what I think of as the "safe" level of dehydration that doesn't affect performance.

I hadn't thought of the idea that you can store more water as you learn to store more glycogen. And as you liberate that glycogen, you liberate the water that's bound to it. So if you use an excess of 300g of glycogen, that's 900g of water-- or about 2 pounds. Very significant.

[MichaelMc]

It seems to be getting missed here that the 3 pounds of water in the example given doesn't evaporate, it is freed into your system, so in effect you just drank another 3 pounds of water. This isn't DEhydration, it is REhydration.

So as you are running along the process is pretty complicated. You sweat a lot of water and a little electrolyte while burning some glycogen and fat. The sweat, glycogen and fat all "disappear" reducing your mass, the freed water partly replaces the water you sweated out. When your electrolyte balance increases, then thirst kicks in and you replace part of the water sweated out. There is no way to know from the weight you lost how much was from fat, glycogen or is actual "dehydration". What you DO have is a really good gauge for electrolyte balance (THIRST) because THAT is the critical factor your body cares about.

As stated, bodies are pretty tolerant of dehydration, and there is some advantage to coming in SOMEWHAT dehydrated at the end of a race. Dehydration is weight loss, and SOME helps, but too much IS too much: unfortunately there is no clear line where "positive" turns to negetive. Some research has shown as little as 3% dehydration can start to impair performance, others show it is still improving running performance until well past 5%. As I think I wrote, 7% weight loss is about standard for the WINNERS or marathons, but I don't think we can apply that across the board by any means. One issue in the studies is that drink companies have done the most research, and it is easy to tilt the balance. For example running inside (stationary) on a treadmill is dramatically different than running outside where the air passing over your body cools it off: this changes the results of research, as do a large number of other factors. You can make the results come out a lot different depending on what you want.

If you are significantly dehydrated you will be unable to spit, then you will find your eyes start feeling very dry. At slightly higher levels your skin feels different when you pinch it (paper-like).

Thirst is an indication your electrolyte level is high: your hydration level is actually independant of that (can be low, can be HIGH). Taking salt tabs or salty drinks throws this indicator off. Some studies have shown Gatorade to WORSEN cases of hyponatremia, as it is salty enough in your mouth to make you thirsty, but it is far less salty than your body chemistry: you dilute your electrolyte level virtually at the same rate as pure water, but it sends the wrong signal to your body. On the opposite side, if you actually are dehydrated Gatorade isn't a good answer either: the carbs in the drink slow the absorption of the water, and if your stomach doesn't want any more calories it will make you reject the fluids. I actually USE Gatorade, so I'm not on a vendetta, by the way.

My suggestions are simple. Drink to thirst, and when you are THIRSTY drink water. When you want to take in carbs and fluids, by all means choose the drink you like (I do use Gatorade). Drink to thirst has proven to be the SAFEST alternative. I should say that Ultras (and IMs) are a different animal than marathons, but similar rules apply.

[Joe Dwarf]

Got a cite for this concept?

[jamix]

As stated, bodies are pretty tolerant of dehydration, and there is some advantage to coming in SOMEWHAT dehydrated at the end of a race. Dehydration is weight loss, and SOME helps, but too much IS too much: unfortunately there is no clear line where "positive" turns to negetive. Some research has shown as little as 3% dehydration can start to impair performance, others show it is still improving running performance until well past 5%. As I think I wrote, 7% weight loss is about standard for the WINNERS or marathons, but I don't think we can apply that across the board by any means. One issue in the studies is that drink companies have done the most research, and it is easy to tilt the balance. For example running inside (stationary) on a treadmill is dramatically different than running outside where the air passing over your body cools it off: this changes the results of research, as do a large number of other factors. You can make the results come out a lot different depending on what you want.

I think I recall Noakes say something along these lines. Once I attempted to put this theory to the test by dehydrating myself for 30 minutes in the sauna and then run on the treadmill to see if I ran faster or slower at 75% maxHR. Unfortunately I never went on the treadmill after my sauna session. I felt really bad. Even though I was sitting down, my heart rate went over 140 in the sauna.

[MichaelMc]

As stated, bodies are pretty tolerant of dehydration, and there is some advantage to coming in SOMEWHAT dehydrated at the end of a race.

I think I recall Noakes say something along these lines. Once I attempted to put this theory to the test by dehydrating myself for 30 minutes in the sauna and then run on the treadmill to see if I ran faster or slower at 75% maxHR. Unfortunately I never went on the treadmill after my sauna session. I felt really bad. Even though I was sitting down, my heart rate went over 140 in the sauna.

Noakes certainly has a lot to say about it.

I'm still sauna averse from my University wrestling days cutting weight. I had to drop from 130 lbs to 119 to weigh in, then wrestle (most of it fluid loss). Of course we put plastic suits on and rode a stationary bike in the sauna to get a serious sweat going. Don't miss that part.

Heart rates go up in saunas as the the body moves blood to the skin in an attempt to cool off.

[Pat Menzies]

I believe dehydration enhances performance up to a point. I always run short races mildly dehydrated.
It is also no coincidence that the best part of a longer race coincides with dropping hydration levels.

[Jwolf]

I believe dehydration enhances performance up to a point. I always run short races mildly dehydrated.
It is also no coincidence that the best part of a longer race coincides with dropping hydration levels.

The best part of whose longer races?

I would guess that dehydration could enhance performance to a point because your body weight is lower. Mild dehydration doesn't cause any danger, and carrying less weight will make you faster. But once you get to a point where your heart rate is rising due to lower blood volume, wouldn't you see a drop in performance? And also why we see a drop in performance in hotter weather- we sweat faster, i.e., the heart has to work harder to pump blood to the body to send that water out for cooling.

[jamix]

I believe dehydration enhances performance up to a point. I always run short races mildly dehydrated.
It is also no coincidence that the best part of a longer race coincides with dropping hydration levels.

I'd be interested to hear how it is you determine how much dehydration is just good enough for performance enhancement.

I've wanted to do this too, but it seems like a real hassle to experiment on my body to determine that just right state. Usually I just warm up before a short distance race by jogging 1-1.5 miles or until I feel ready.

[Jwolf]

I believe dehydration enhances performance up to a point. I always run short races mildly dehydrated.
It is also no coincidence that the best part of a longer race coincides with dropping hydration levels.

I'd be interested to hear how it is you determine how much dehydration is just good enough for performance enhancement.

I've wanted to do this too, but it seems like a real hassle to experiment on my body to determine that just right state. Usually I just warm up before a short distance race by jogging 1-1.5 miles or until I feel ready.

You're not going to dehydrate yourself substantially in your warmup jog. I think it depends more on how much you drink in the 24 hours leading up to the race. You see people pulling off the course to pee 10 minutes into the race, and then again soon after -- these people are likely overhydrated.

Anecdotally, I've had my best races when I've had a salty meal the night before the race and just drink to thirst. My body seems to hold on to a good amount of water. And I never have to stop to pee.

[jamix]

I've heard that drinking a lot increases sweat rate and can cause a diuretic effect, though not right away.

[turd ferguson]

Drinking to thirst can be tricky, though. Many of us don't know what "thirst" feels like, especially in race conditions.

This.

I don't disagree with anything said above - its been a great discussion and makes a lot of sense. You see people overhydrating all the time - a little is good so a lot must be better. So you see people carrying water bottles and fuel belts and hitting all 3 aid stations in a 5k.

But I don't trust my thirst either. My mouth is often very dry, and once I get running and breathing through my mouth, it gets worse and worse - my conscious brain knows I'm not dehydrated 15 minutes into my run but my mouth is dry, so I've learned to ignore those signals. I end up drinking to a schedule instead - roughly a bottle an hour on the bike, a bottle an hour on runs lasting longer than 2 hours (starting in the 2nd hour). Works for me.

[La]

Medication can have an effect, too. My allergy meds make my mouth very dry, and running makes it worse.

The worst "thirst" I've ever felt was at the top of the climb at Yellow Lake at IMC 2006. I'd been drinking Eload all day (and boosting that with Eload caps) and with the sweat pouring down my face into my mouth, I could barely get the word "water" out to the volunteer at the aid station.

[MichaelMc]

Good discussion.

Theory and studies can help us open our minds to other possible solutions, but shouldn't shut off our own minds and senses. If you KNOW you can't trust your own thirst then don't. On the other hand don't discard your body's input in favor of some pseudo-scientific formula either. As the study points out, weight loss does NOT equal dehydration, and this is not common knowledge.

Hydration is a subject I'm passionate about because people die unneccessarily from hyponatremia, and drink marketing contributes to it. The death rate in marathons dropped significantly when the medical advice changed from "drink early, drink often" to "drink when you're thirsty". It isn't like droves of people were dropping, but it bothers me when science and marketing are used to push unhealthy advice. IMO the marketing push has switched from "guzzle sports drink" to "guzzle sports drink AND electrolytes", with no supporting evidence it alleviates the problem the original advice created.

If people were simply left to their own devices to determine how much fluid to take in rather than being given dire warnings to "drink more" and "don't drink so much", I'd be happy, but the genie is out of the bottle. In the current age of the mass participation marathon we have many people in a big hurry to run their fastest possible marathon. Everyone is looking for the "secret" of running as fast as they can for as far as they want, which makes us very vulnerable to people marketing "snake oil" or simply bad advice.

For me the hydration equation is simple. The day before the race I keep water near me and take a drink whenever I feel like it, but I never try to drink. In the morning I have my normal coffee and make sure I'm not the slightest bit thirsty. I can tell by my urination rate when I'm fully hydrated, then I STOP drinking. Once the race starts I take in sports drink (if that is my carb source) on a schedule and drink water whenever I'm thirsty. I grab a cup of water almost every water stop, but most of them go ON MY HEAD. If I think I might be thristy I take a sip, if I feel like it I drink the rest, if not, over my head to cool myself off. When I finish races I'm thirsty, but not REALLY thirsty: usually I can't finish the bottle I get at the finish line for some time.

If you can still spit, you aren't significantly dehydrated: it is a pretty simple test. If you can't spit, then see if your eyes feel dry and your skin feels thin and papery; you should probably see if you can settle your stomach and take in water. Unfortunately heat, dehydration and overhydration all cause headaches, dizziness, confusion and nausea: during a race the effects of each plus high exertion and fatigue make it hard to decide what is happening. Medical personnnel have a hard time telling whether to give fluids or withold fluids. I find the advice to ignore your body and go with some formula to be generally bad. I prefer the idea of really LISTENING to my body, and this has proved to be the safest advice for runners generally. Your mileage may vary...