From: rns@npg-sd.SanDiegoCA.NCR.COM (Rick Schubert)
Newsgroups: rec.running
Subject: Re: sweat
Date: 25 Aug 92 19:55:29 GMT
Organization: NCR Corp., Network Products - San Diego

In <1992Aug24.154028.2962@colorado.edu> jac@noaacrd.colorado.edu (Julia Collins) writes:

>In article <kpalm.714351820@athena> kpalm@athena.qualcomm.com (Kent Palm) writes:
>>Is it possible to drink so much water everyday, that the body becomes
>>so accustomed to the never ending supply, it begins to function as
>>though it really has a never ending supply?
>>
>>Since the body thinks it has unlimited fluids, then during exercise,
>>the body "generously" sheds water to cool itself, dehydrating the
>>individual and losing needed trace minerals much faster than is
>>necessary.

>I don't think anything will be lost faster than "necessary". 
>The body will take advantage of being well-hydrated by being able to
>sweat enough to keep the body core temperature down.

If I correctly understand your point, this is not consistent with what
I have read.  Sorry, I don't have any references; it's just stored somewhere
deep in my memory.  If I remember correctly, the main purpose of heat
conditioning is to train the body to sweat more, which is important because
sweating cools the body.  You seem to be saying that the amount of sweat
is just a function of the amount of heat produced and the temperature.
Now if the theory about training ones body to sweat more is true, there may
be some concern about drinking too much and becoming dehydrated.  I
definitely sweat more when I drink more: recently I ran 12 miles in hot
weather.  I drank 7 pints of water before and during the run, yet I came
back 6 pounds lighter than when I started.  This means I sweated 13 pints
worth.  If I hadn't drunk any water, I would either be dead or would have
sweated less.  I think the body has a mechanism that regulates the amount
of sweating by how much water it has available.  Of course, you can't sweat
what you don't have, but I think that sweating decreases before you are
totally depleted of water (in which case you would be dead).

>work produces heat as a by-product since the body isn't 100% efficient.
>If left unchecked, your core temperature can rise to dangerously high
>levels.  Thus it's to your advantage to keep well-hydrated: you'll be 
>able to handle the cooling needs of high work levels. 

No question about that.  The question, though, was whether taking in water
at a greater rate than your body can absorb it, you may fool your body
into thinking it has more water available (i.e. usable) than it actually
has.  I think there is definitely a concern here, but I do not know enough
physiology to conclude that drinking too much water would be a problem.
I've heard that it can be a problem, but in a different sense.  I remember
reading about or watching an ultra-marathon (probably the Western States 100)
in which one of the competitors had problems from over-hydration.  I don't
remember clearly, but I think the problem there was with an electrolyte
imbalance, which isn't the concern here.

>>
>>The real problem occurs when trying to stay hydrated for an endurance
>>event with a limited water supply; the body continues to shed water too
>>fast.  And even with an unlimited water supply, the stomach cannot
>>absorb the water nearly as fast as the body is shedding it.

>It's not shedding water "too fast," it's shedding it as fast as it can. 

I don't think that's true, as I've noted above.

>If you're working hard, your core temperature will begin to rise.
>If your core temp starts to rise, you're gonna sweat! And you're going 
>to sweat in direct proportion to the amount of work that you're doing, 
>or at least the body will try to sweat this much. If you start to become 
>dehydrated to the point where blood volume is reduced, then sweating is 
>decreased to protect blood volume/blood pressure needs.

Well, maybe this is part of the mechanism that I've noted.  You may be
right, but I don't think so.  But then, what do I know?

>                                                              In general,
>it's a bad idea to try to "train" your body to survive on less water.

I agree with this.  But this doesn't contradict my point or the question
being asked.

>You'll just be dehydrated most of the time, and you won't achieve the
>performance you otherwise would if you stayed as hydrated as humanly possible.

... up to a point, perhaps.

-- Rick Schubert (rick.schubert@SanDiegoCA.NCR.COM)