Beware Overhydration (Read 1182 times)

I'm always a bit confused by this.  It's not just simply drinking too much, but more specifically drinking too much water to replenish what you lost through sweat, but not replenishing the sodium you lost, thus creating an imbalance.  

What if you were to drink too much water, but also took electrolyte supplements.  Wouldn't you be OK? 

But it's much simpler and more easily understood to tell a marathoner, "don't over-hydrate, drink to thirst" than it is to tell them, "make sure you maintain hydration and balance your sodium and potassium levels with adequate water and electrolyte supplementation."

Don't drink too much, drink to thirst. Drinking when you aren't thirsty is stupid. Plus, you'll pee a lot, possibly affecting your time. That's easily understood advice. 

I am a big guy 200+ with a very high sweat rate.  The more I run / sweat the more likely I cannot keep hydrated drinking to thirst.  If I am running about 100 miles per week - I can get by with 120-150 ouces of water a day.  When I start hitting 150+ it is 180-200 ounces per day.  I also take s-caps and potasium when I am drinking a lot.

Most skinny ass runners with normal sweat rates would not be drinking a gallon of water a day.

This is an area that still puzzles me a bit. Of course, hyponatremia is a real problem, and it can happen even when drinking Gatorade instead of water -- in fact, the electrolytes in every "electrolyte drink" don't make a whole lot of difference. Drinking any of them still reduces your blood electrolyte concentration. This is very worthwhile reading:

http://www.sportsscientists.com/2007/11/sports-drinks-sweat-and-electrolytes.html

But. For marathoners, there are other considerations. One, dehydration reduces blood volume, impacting performance. Two, marathoners need fuel during the race, and absorbing the fuel requires water -- whether it's pre-mixed in the form of Gatorade, or in gels that require an equivalent amount of water to absorb.

So it seems to me that there is a fundamental tension here. If you only drink when thirsty, your performance must inevitably suffer. But this tension isn't something I ever see addressed anywhere.

Take that link above. Part of the conclusion reads:

"So bottom line - drink to thirst, don't worry too much about what you drink, but just make sure you are getting enough ENERGY in - the one thing that the sports drinks provide that is required is glucose, and so plain water is unlikely to be sufficient for longer than about 2 hours of exercise." (I really, really wish every marathon RD would read this -- there is way too much Ultima or Nuun on marathon courses.)

If you drink to thirst, you are just not going to be getting enough energy in! When I run Boston, I drink Gatorade at roughly 2/3 of the aid stations -- which are spaced every mile. That's a lot of fluid. Is it too much? Maybe. But I tell myself I need those carbs.

It takes at least 7 days to properly hydrate muscles

 

If you cram loads of fluids in the last 48 hours you are mostly just stripping your electrolytes. 

What does that mean, exactly? I normally do a one-day marathon carb load ("Western Australia method"). As muscles absorb glycogen, they necessarily absorb extra water. (Which, incidentally, is why it's stupid to try to avoid losing any water weight on long runs -- you burn glycogen; water leaves your muscles. You can't put it back without more glycogen.)

Well fair enough. And so yes, the "don't overhydrate" message is important for new marathoners.

But are we only talking about new marathoners here? What about the rest of us?

I would also submit that most people take in more calories than they realistically need to perform during a marathon as it is.

Interesting article, and to make this topic more inflammatory, we could conclude that Sports Drinks are Bunk.  Salt Tablets are Bunk.

We haven't addressed the sugar part of it, but Kool-Aid or fruit juice would be as good as Gatorade for that.  Candy might be better, if overhydration is a concern.